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Parental investment: How an equity motive can produce inequality

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Abstract

The equity heuristic is a decision rule specifying that parents should attempt to subdivide resources more or less equally among their children. This investment rule coincides with the prescription from optimality models in economics and biology in cases in which expected future return for each offspring is equal. In this article, the authors present a counterintuitive implication of the equity heuristic: Whereas an equity motive produces a fair distribution at any given point in time, it yields a cumulative distribution of investments that is unequal. The authors test this analytical observation against evidence reported in studies exploring parental investment and show how the equity heuristic can provide an explanation of why the literature reports a diversity of birth order effects with respect to parental resource allocation.

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... To reduce this uncertainty, grandparents preferentially invest in those grandchildren whose parents are most likely to reciprocate in the future. Moreover, despite a tacit and widespread norm in modern societies to invest in children and grandchildren equally (Hertwig, Davis, & Sulloway, 2002), this utility perspective promotes favouritism, which, surprisingly, is consistently found in self-report measures (Suitor, Sechrist, Plikuhn, Pardo, & Pillemer, 2008). Informatively for the current interdisciplinary perspective on grandparents, favouritism of children by parents, whether intentional or not, varies by family stress (e.g. ...
... divorce), family structure (e.g. birth order), biological relatedness, birth order, behaviour and personality (Hertwig et al., 2002;Suitor et al., 2008). Although the rational-grandparent model ignores important issues (e.g. ...
... In industrialised societies, in contrast, the impact of sibling help for child care is likely to be low because siblings are few, closely spaced and contribute little to the family economy (Sear & Coall, 2011). In both cases, a larger family size, ceteris paribus, dilutes the resources available for each child (Blake, 1987;Hertwig et al., 2002;Marks, 2006) and grandchild (Coall, Meier, Hertwig, Wänke, & Höpflinger, 2009;Uhlenberg & Hammill, 1998). ...
... Parents invest more in earlier born children and these individuals have a greater tendency to "not take unnecessary chances [or risks]" (Grable & Joo, 2004: 81). In contrast, later-born children tend to receive less parental investment and resources (Hertwig, Davis, & Sulloway, 2002). Evolutionary theory thus suggests that younger siblings are more likely to engage in risky behaviors to try to "recalibrate parental investment in their favor" (Sulloway & Zweigenhaft, 2010: 414). ...
... In considering what behaviors siblings use to deal with sibling rivalry and gain parental favor, we theorize that the earlier a sibling is in the birth order, the less they will attempt to garner parental investment and thus the lower their tendency to engage in risky behaviors to carve out a niche. Scholars note that earlier born children tend to be endowed with greater parental resources (Hertwig et al., 2002). This is partly because older siblings "tend to be larger, stronger, and more intellectually developed than their" younger siblings (Freese, Powell, & Steelman, 1999: 211). ...
... Later-born siblings, in contrast, tend to receive less parental investment and resources (Hertwig et al., 2002), and we thus theorize will take greater risks to establish a niche to gain attention and material support. Scholars note that, "In a Darwinian world," risk taking is "adaptive wherever the chances of survival or reproduction are limited" (Sulloway & Zweigenhaft, 2010: 414). ...
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The importance of birth order has been the subject of debate for centuries and has captured the attention of the general public and researchers alike. Despite this interest, scholars have little understanding of the impact birth order has on CEOs and their strategic decisions. With this in mind, we develop theory that explains how CEO birth order may be associated with strategic risk taking. Drawing from evolutionary theory arguments related to birth order, we theorize that CEO birth order is positively associated with strategic risk taking; that is, earlier born CEOs will take less risk than later-born CEOs. As evolutionary theory proposes that birth order effects are driven by sibling rivalry, we also argue that this relationship is moderated by three factors related to sibling rivalry: age gap between a CEO and the closest born sibling, CEO age, and the presence of a sibling CEO. Our results provide support for our theorizing and suggest that birth order may have important implications for organizations. We believe this study helps advance strategic management research, the broader multi-disciplinary “family science” literature, and the much needed cross-pollination of ideas between the two.
... The confluence perspective (Zajonc et al. 1979), suggests that nonmaterial resources (e.g., richer verbal environment) increase in larger families (Zajonc and Sulloway 2007). However, Hertwig et al. (2002) asserted: BAn only child receives the most resources, followed by children in a two-child family, whereas children in a three-child family receive the least^(p. 731). ...
... 731). Hertwig et al. (2002) referred to the parents' cumulative investment, the resources available to an only child over four years. Their calculations, based on the proportion of the parents' allocation of the resources they have for an only child, show that children in a two-child family receive 62.5% each, and children in three-child family receive 54%, 41.5% and 54% respectively. ...
... Their experience enables them to advise their younger siblings and support them (Feinberg et al. 2012;Furman and Buhrmester 1985) and they tend to dominate the sibling relationship (Hoffman 1991). Hertwig et al. (2002) described greater privileges often granted to firstborn children, such as permission to borrow the car or to stay out late. ...
Article
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Most studies on the quality of sibling relationship in families with gifted and non-gifted children have been conducted in two-child families and yielded mixed results. The current study, with 142 participating parents, addresses parents’ perception of this relationships among gifted and one or two non-gifted sibling in association with birth order and children’s sex. The parents completed an online survey using the Sibling Relationship Questionnaire (SRQ) for first- and second-order factors. A MANCOVA of mean differences showed no significant first-order factor differences in quality of sibling relationship between the two groups. One significant difference in second-order factors was found, with “admiration of sibling” score higher in families where the gifted child was the second or third born, not first born. Results provide further support for the notion that there are no negative consequences on offspring relationships when a child has a gifted sibling.
... Several views have been proposed to explain the general superiority of only children in tasks demanding creativity. The most dominant explanation, based on the parental cumulative resource distribution view or resource view (Hertwig, Davis, & Sulloway, 2002) holds that with certain parental resources, the greater the number of children, the smaller the amount of resources each child receives. As such, it is not surprising that an only child receives the most resources. ...
... As such, it is not surprising that an only child receives the most resources. Regarding the cumulative investment, only children receive 100% of parental resources, children in two-child families receive 62.5% each, and children in three-child families receive 54%, 41.5%, and 54% respectively (Hertwig et al., 2002). A second explanation, based on the autonomy view, holds that only children may develop a different type of personality from children with siblings due to the absence of interaction with siblings. ...
... Previous studies on creativity have indicated that people with better cognitive abilities tend to have higher creativity (Gedo, 1997;Simonton, 2000). Furthermore, the parental cumulative resource distribution view (Hertwig et al., 2002) posits that only children may receive 100% resources from their parents in the absence of competition from other siblings. In such family environments, only children have more interaction and communication with their parents, which in turn, may promote their creativity (Chan, 2005;Domino, 1979). ...
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The purpose of this study was to examine the influences of sibling constellation (sex and birth order) on creativity in the context of China's one-child policy and Confucian culture (e.g., preference for male offspring). Participants were recruited from a public university in east China and were asked to complete two divergent thinking tests, including a Line Meaning test and a Real-World Problem test. Data collected from those born in or after 1979 (the year OCP was implemented in China) were selected. The sample was further divided into six groups for comparisons including first son, first daughter, later son, later daughter, only son, and only daughter. Results indicated that only children exhibited significantly higher abilities in visual imagination (line meaning) tasks than children with siblings. Further, testing revealed that only daughters exhibited the highest abilities, both in visual imagination (line meaning) and creative problem solving (real-world problems) as compared to other sibling constellation groups. Specifically, only daughters scored higher than later daughters in visual imagination. They also showed higher abilities than first sons in both types of creative potential tests. Implications are further discussed in the paper.
... The oldest group's parents were not permitted to favor any of their sons for large wealth transfers because, in theory, all sons received land of equal size and quality from the government; furthermore, this sweeping policy likely affected other types of parental and kin investment besides wealth transfers. Studies of parental investment in the context of equal resource access suggest that first-and lastborn children tend to be advantaged over middle-born children (Hertwig et al. 2002), who receive fewer cumulative investment owing to competition with younger and older siblings. Faurie et al. (2009) corroborated Hertwig et al. (2002) finding among sons of rural preindustrial Finns: middle-born sons appeared to produce significantly fewer offspring than first-or lastborn sons. ...
... In the context of limited resources, firstborn sons might interact more with parents and with nonparental kin compared with other birth-order categories because firstborn sons represent a less risky investment for lineage survival (Gibson and Gurmu 2011;Hrdy and Judge 1993). Later-born sons, being disadvantaged in terms of kin interactants, might diversify their networks to include nonkin, possibly through reciprocity 2. For farmers who received their land from the government without discrimination, first-and lastborn sons might have enjoyed extraparental investment in terms of cumulative investment in their lifetimes (Faurie et al. 2009;Hertwig et al. 2002;Kidwell 1982;Sulloway 1996). If those differences held into adulthood, middle-born sons might still represent worthwhile investment for nonparental kin, especially if they are more active in diversifying their networks. ...
... Support networks considered here include daily support for farming and domestic activities, such as help with farm activities (plowing, planting, weeding, cattle herding, and gifting or loan of seeds, crops, and other materials, including animals), help with domestic activities (gifting or loan of food, clothes, money, water, firewood, or other materials), help during sickness (transport or care), help with house construction, and ceremonial duties. Because firstborn and lastborn sons might enjoy additional extraparental investment (Faurie et al. 2009;Hertwig et al. 2002;Kidwell 1982), and because birth rank does not discriminate for the lastborn category, we used three intrasex birth-order categories (firstborn, middle-born, and lastborn sons) instead of birth rank. Thus, only heads of household with at least two brothers born from the same father, who survived until fifteen years of age, were included in the models (N = 331). ...
Article
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Social support networks play a key role in human livelihood security, especially in vulnerable communities. Here we explore how evolutionary ideas of kin selection and intrahousehold resource competition can explain individual variation in daily support network size and composition in a south-central Ethiopian agricultural community. We consider both domestic and agricultural help across two generations with different wealth-transfer norms that yield different contexts for sibling competition. For farmers who inherited land rights from family, firstborns were more likely to report daily support from parents and to have larger nonparental kin networks (n = 180). Compared with other farmers, firstborns were also more likely to reciprocate their parents’ support, and to help nonparental kin without reciprocity. For farmers who received land rights from the government (n = 151), middle-born farmers reported more nonparental kin in their support networks compared with other farmers; nonreciprocal interactions were particularly common in both directions. This suggests a diversification of adult support networks to nonparental kin, possibly in response to a long-term parental investment disadvantage of being middle-born sons. In all instances, regardless of inheritance, lastborn farmers were the most disadvantaged in terms of kin support. Overall, we found that nonreciprocal interactions among farmers followed kin selection predictions. Direct reciprocity explained a substantial part of the support received from kin, suggesting the importance of the combined effects of kin selection and reciprocity for investment from kin.
... As siblings compete for attention and resources from parents, different family niches develop for children with different numbers of siblings [29,30]. On the one hand, only children are not exposed to sibling rivalry and receive parental investment naturally. ...
... On the one hand, only children are not exposed to sibling rivalry and receive parental investment naturally. The existing literature suggests that children with more parental attention are more likely to have positive attitudes towards family compared to those receiving less parental attention [29,30]. On the other hand, children may avoid risky sexual behaviors through the sibling effect. ...
... According to previous research, the SRH of young people may be negatively or positively affected by siblings. Competition for parental attention and resources results in negative effects [29,30], while instructions and communications regarding sexuality between siblings are often helpful in preventing risky sexual behaviors in young people [24,31,32]. Overall, our findings support that sibling rivalry was more prevalent among Chinese young people, and having more siblings was associated with risky sexual behaviors and negative SRH. ...
Article
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Only children are more prevalent among young people today in China due to the globally renowned one-child policy since the 1980s, but the association between sibship size and the sexual activity of youth needs to be further clarified. The aim of this study was to explore the effect of siblings, being an only child, and birth order on the sexual and reproductive health (SRH) of young people. Data were utilized from 11,044 sexually active college/university students who participated in a large-scale national survey. Overall, numerous undergraduates nationally identified as only children (43.5%); for non-only children, 32.4% were oldest children, 10.5% were middle children, and 13.6% were youngest children. For both sexes, having more siblings was related to having risky sexual debuts and less contraceptive use. Furthermore, young men and young people born in rural areas with more siblings were more likely to have severe health outcomes, such as unwanted pregnancy and sexually transmitted infection(s). Finally, being an only child protected youth from risky sexual behaviors and adverse health outcomes. For students with siblings, middle children were more inclined to risky sexual initiation and low frequency of contraception compared to first-borns. Our analysis provides the first evidence of one child and sibling effects on SRH in China and has significant implications for promoting SRH in the context of encouraging childbirth.
... Parents invest more in earlier-born children and these individuals have a greater tendency to "not take unnecessary chances [or risks]" (Grable & Joo, 2004: 81). In contrast, laterborn children tend to receive less parental investment and resources (Hertwig, Davis, & Sulloway, 2002). Evolutionary theory thus suggests that younger siblings are more likely to engage in risky behaviors to try to "recalibrate parental investment in their favor" (Sulloway & Zweigenhaft, 2010: 414). ...
... In considering what behaviors siblings use to deal with sibling rivalry and gain parental favor, we theorize that the earlier a sibling is in the birth order, the less they will attempt to garner parental investment and thus the lower their tendency to engage in risky behaviors to carve out a niche. Scholars have noted that earlier-born children tend to be endowed with greater parental resources (Hertwig et al., 2002). This is partly because older siblings "tend to be larger, stronger, and more intellectually developed" than their younger siblings (Freese, Powell, & Steelman, 1999: 211). ...
... Later-born siblings, in contrast, tend to receive less parental investment and resources (Hertwig et al., 2002), and thus, we theorize, will take greater risks to establish a niche to gain attention and material support. Scholars have noted that, "In a Darwinian world," risk taking is "adaptive wherever the chances of survival or reproduction are limited" (Sulloway & Zweigenhaft, 2010: 414). ...
... And some parents even change their investments when their children's academic ability declines (Quadlin, 2015). The second type is compensation, which means compensatory parents tend to invest in low-performance children (Hertwig, Davis & Sulloway, 2002;Quadlin, 2015). Therefore, children who were not good at studying or with poor health were found to get more attention, time, care, and investments from their parents (Abufhele, Behrman & Bravo, 2017;Hertwig, Davis & Sulloway, 2002;Quadlin, 2015). ...
... The second type is compensation, which means compensatory parents tend to invest in low-performance children (Hertwig, Davis & Sulloway, 2002;Quadlin, 2015). Therefore, children who were not good at studying or with poor health were found to get more attention, time, care, and investments from their parents (Abufhele, Behrman & Bravo, 2017;Hertwig, Davis & Sulloway, 2002;Quadlin, 2015). And these parents might actively intervene in their children's studies to prevent future failures (Quadlin, 2015). ...
... On the one side, the existing studies have examined the effect of the only-child family on academic achievement in urban adolescents; very few studies have explored the only-child family from rural areas, leaving the onlychild families in rural areas unexplored. On the other side, some scholars have also found that children's performance might not necessarily determine parental investment; instead, some parents might provide maximum resources by their socioeconomic status (SES) and other factors (Hertwig, Davis & Sulloway, 2002;Perna, 2006;Quadlin, 2015). Therefore, to understand the role of family size in influencing academic performance more clearly, our study will explore the differences and influencing factors of academic achievement between onlychild families and multi-child families; moreover, the family SES effect will be discussed and examined in the following section. ...
Article
The impact of the one-child policy on urban children's development has been widely studied, leaving those from rural areas unexplored. This study investigated the sibling effects (only-child or not) on adolescents’ academic achievement in rural China. Altogether 156 pairs of only children and their peers with siblings (Female = 145, 46.5%; aged from 13-17; Mage = 14.83) were sampled and matched from rural schools; then they completed the Program for International Student Assessment (PISA) Math, Reading, and Science tests and parental questionnaires. The descriptive and hierarchical regression results indicated that the adolescents with siblings had significantly higher academic achievement, parents’ academic expectation, desk ownership, and kindergarten level than the only children. In addition, kindergarten level, eyesight, and parents’ academic expectations were significant predictors of rural adolescents’ academic achievement. These findings suggested that: (1) the educational authorities should build an equitable preschool learning situation; (2) teachers should lead only children to set and make progress on educational goals; (3) parents should raise the awareness of protecting children’s eyesight in those remote and rural areas.
... Birth order represents a social determinant of individual development, which strongly affects the propensity to adopt certain behaviors and attitudes. Indeed, given competition between siblings for parental attention and resources, individual siblings try to distinguish themselves from one another in order to establish a unique familial niche from which to elicit parental attention (Hertwig et al., 2002;Sulloway, 1996). Indeed, differences in parental investment and competition for power, attention and personal gain is a result of the natural hierarchy developed when a new-born comes into the family (Cole, 2014;Sulloway, 2007). ...
... Indeed, differences in parental investment and competition for power, attention and personal gain is a result of the natural hierarchy developed when a new-born comes into the family (Cole, 2014;Sulloway, 2007). Siblings receiving more parental investment are expected to have more positive emotions toward the family and less unconventional behaviors compared with siblings receiving less parental attention (Bu & Sulloway, 2016;Hertwig et al., 2002). Thus, with the aim of increasing parental attention, younger siblings may develop attitudes and qualities that generally make them more rebellious, more open to new experiences and more likely to adopt risky behaviors. ...
... As first-borns begin life as only children and thus are not born into experiences of sibling rivalry, they display beliefs and personality traits that mirror their parents and are generally more likely to be responsible and conform to parental authority, while later-borns often behave in the opposite way (Sulloway, 1996(Sulloway, , 2007. Sulloway's approach has been called "niche portioning" since it suggests that while first-borns act as surrogate parents, later-borns are family newcomers seeking an open niche within the family (Hertwig et al., 2002). Empirical controlled studies have reported that first-borns are more conscientious and more responsible than later-borns who, by contrast, appear to be more agreeable, accommodating and affectionate (Healey & Ellis, 2007). ...
Article
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Birth order may foster specific roles for individuals within the family and set in train a dynamic that influences the development of specific behaviors. In this paper, we explored the relationship between birth order, sex, timing of sexual initiation, and its consequences for risky sexual behavior and sexual health. We conducted a path analysis to simultaneously estimate direct and indirect effects using data from the National Survey of Sexual Attitudes and Lifestyles (NATSAL-3). Whereas women born as only-children were more likely to sexually debut at later ages, middle-child boys were significantly more prone to initiate sexual intercourse earlier compared with first-borns. As expected, early sexual initiation was associated with riskier behaviors and sexual health outcomes. These associations were partially moderated by siblings role as confidants about sexuality. Our findings have implications for preventive programs aimed at promoting healthy sexual debuts and behaviors over the life span.
... The birth position of the lastborn child has also been argued to elicit heightened investment by parents, since this child typically has the highest need (Daly and Wilson, 1984;Kidwell, 1982;Rohde et al., 2003;Salmon and Daly, 1998). Therefore, parental investment has been argued to follow a curvilinear pattern (Hertwig et al., 2002) with middleborns receiving relatively less investment than firstborns and lastborns, given that middleborns only have a limited period where they are the only child for parents to invest in. ...
... While firstborns are the only child in the family for a certain period of time before the second child is born, lastborns are likely to remain the only child in the household after older siblings leave home. In contrast, middleborns, most likely, must share parental resources at all times during their development (Hertwig et al., 2002;Lindert, 1977;Price, 2008). In sum, middleborns have been argued to end up with fewer (parental) resources and quality time than other birth orders (Kidwell, 1982;Rohde et al., 2003;Salmon and Daly, 1998;Sulloway, 1996). ...
Article
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Middleborns have been argued to be the neglected birth order. The present study aimed to test whether the emotional closeness to parents, siblings or friends differed between middleborns and otherborns, across two different datasets. Using a between family design this study accounted for gender, nationality, educational attainment, age and sibship size via matching. We found no evidence to suggest that middleborns differ from otherborns in familial sentiment. The sign of closeness to friends was in the opposite direction than predicted, with middleborns being less close than other birth orders. The findings are discussed with reference to current literature on birth order and familial sentiment.
... In Chinese culture, several factors may contribute to the creativity advantages of only children. First and most importantly, compared with children with siblings, only children received almost all the educational resources from their parents (Hertwig, Davis, & Sulloway, 2002), and had much more opportunities than children with siblings to interact with parents . This resource-sufficient family environment could encourage and facilitate children to generate and eventually implement creative ideas (Chan, 2005;Hunter, Bedell, & Mumford, 2007). ...
... In this study, we found that only children's creativity advantages varied with family type. While only children from all the families achieve relatively higher creativity scores than children with siblings, the significant advantage was only found in the only children from NF, as showed in Fig. 5. Considering the only children from NF did not have significant advantage in family SES and intelligence, as showed in Table 1, one reasonable explanation of the results is that the only children from NF have much more opportunities to interact with parents (Hertwig et al., 2002) and much more resources to implement their creative ideas (Hunter et al., 2007). Another possible explanation is that, because the only children from NF have less adults and peers to interact than children with siblings, they have developed higher levels of autonomy and thereby enhanced their creative thinking (Liu et al., 2013). ...
Article
It is not uncommon in China that children are raised by both parents and grandparents in an extended family. The purpose of this study is to investigate the effects of three-generational families on Chinese children's creativity. A sample of 1710 elementary school students aged 6–13 was drawn from two schools in urban districts of Shanghai. Participants’ creativity was measured by the Torrance Test of Creative Thinking-Figural (TTCT-Figural) and Alternate Uses tasks (AUT) and their family demographic information was obtained from parents’ report. The results indicated that (1) the co-parenting of grandparents and parents had a negative effect on children's creativity; (2) children growing up in the three-generation families, particularly in the grandparents-headed families, had lower creativity than those from families living without grandparents; (3) compared with girls, boys raised in the three-generation families were more likely to show disadvantages in creativity development; (4) only children overall showed significantly higher creativity than children with siblings, but this advantage was more salient for only children raised in nuclear families than in three-generation families. These results are explained on the basis of parental investment theory. We further conclude that the quality of cognitive and interpersonal resources in a family, such as intellectual stimulation and general encouragement, matter more than the simple accumulation of family resources in predicting children’s creativity.
... In research, children whose orderof-birth puts them between the first and last born are grouped together and called middle borns. The number of siblings in the family, referred to here as sibship size, also influences the effects of birth order, not only by determining the number of middle borns in a family, but also by limiting the amount of parental investment available for individual children (Hertwig et al., 2002). In most research and theory, sibling effects have been portrayed as fixed, even though many sibling effects, including those associated with birth order and sibship size, are dynamic during the early years of childhood. ...
... There are several mechanisms potentially contributing to this greater creativity among only children; three are described here. The first involves the fact that one-child parents can invest all their resources, including attention and affection, into supporting their single child's development (Hertwig et al., 2002). Parental investment is thought to promote the intellectual and socioemotional development of children generally, and the fact that only children get more parental investment than other children probably accounts for their greater intellectual abilities and self-esteem (Falbo and Polit, 1986). ...
... Siblings -and thus birth order and the sex composition of siblings -can be expected to have an impact on economic preferences because siblings compete for parental attention. As a consequence, children adapt their behavior to reach this goal, which may lead to differentiate one's behavior from siblings' behavior to capture more parental attention (Sulloway, 1996;Hertwig et al., 2002). Yet, besides this tendency to show different behavior than one's siblings, siblings may also have the opposite effect of assimilating behavior, because siblings can learn from each other through imitation (Rust et al., 2000). ...
... First born children usually have access to more family resources than later born ones (Sulloway, 1996). For example it has been shown that first born children spend more quality time with their parents than second born children, even when parents try to divide their time equally between their offspring (Hertwig et al., 2002;Price, 2008). ...
... Natural selection would therefore favour specific parental behavioural strategies aimed at maximising fitness by investing more in children with greater productive value. In turn, parental favouritism depends on the perceived reproductive value of each child and investments take place in proportion to their expected fitness (Clarke and Low 2001;Hertwig, Davis, and Sulloway 2002;Veller, Haig, and Nowak 2016). This may be especially important when comparing non-adopted and adopted children with each other, as adopted children are mostly not related to their adoptive parents. ...
... Indeed, in most cases parents, or other kin, are the ones who are actually distributing resources, which will impact nutritional status, the incidence of morbidity and the likelihood of fatality from illness and accidents. Moreover, even in the absence of any strategic behaviour of parents and kin, or in cases when parents distribute resources strictly equally to all children, inequalities may arise because there is simply less to divide when there are more children in a household (Bras 2014;Hertwig, Davis, and Sulloway 2002). The term 'sibling rivalry' therefore only denotes the situation when available resources are divided between children within a household, which in turn can have 12 It is important to note that the model tries to capture generalities. ...
Thesis
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Although the historical Dutch and Taiwanese populations studied are very different, sibship size and composition influenced the survival of infants and children in both. In general, the presence of siblings led to higher infant and child mortality risks. This is in line with what we know about sibling rivalry and parental investment, which suggest that parents need to make decisions regarding the amount of resources to allocate to each child. Yet, my study also demonstrates that the way siblings influenced infant and child mortality risks differs within and between the Netherlands and Taiwan due to regional variation in economic conditions, cultural norms, and household organisation. My dissertation therefore gives insight into the conditions under which siblings have an effect on the creation of health inequalities. This is important, since this subject not only has broad implications for how we understand the lives of our predecessors, but also those of ourselves. ISBN: 978-94-6421-024-8
... Similarly, in monetary gambles, when choosing between several uncertain options, the equiprobable heuristic treats all outcomes as if they were equally likely. A modification of the equal-weighting heuristic for resource allocation tasks, the 1/N heuristic, distributes resources equally between the available number of options (DeMiguel et al. 2007;Hertwig et al. 2002). ...
... But the mere discovery of this heuristic entails neither an explanation of its behavioral origin nor an account of psychological processes involved in its use. Equal diversification of resources (under the assumption that they are not extremely scarce) is a strategy that can be found in both humans and animals (e.g., in the case of parental investment; see Davis and Todd 1999;Hertwig et al. 2002). In a similar vein, using heuristics does not mean dispensing with probability and statistics. ...
Article
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Despite the ubiquity of uncertainty, scientific attention has focused primarily on probabilistic approaches, which predominantly rely on the assumption that uncertainty can be measured and expressed numerically. At the same time, the increasing amount of research from a range of areas including psychology, economics, and sociology testify that in the real world, people’s understanding of risky and uncertain situations cannot be satisfactorily explained in probabilistic and decision-theoretical terms. In this article, we offer a theoretical overview of an alternative approach to uncertainty developed in the framework of the ecological rationality research program. We first trace the origins of the ecological approach to uncertainty in Simon’s bounded rationality and Brunswik’s lens model framework and then proceed by outlining a theoretical view of uncertainty that ensues from the ecological rationality approach. We argue that the ecological concept of uncertainty relies on a systemic view of uncertainty that features it as a property of the organism–environment system. We also show how simple heuristics can deal with unmeasurable uncertainty and in what cases ignoring probabilities emerges as a proper response to uncertainty.
... Thus, structural factors in the family of upbringing-such as number of siblings and the position among them-may have important implications later in life (Kolk 2014a;Murphy 1999), due to siblings getting a different share of a limited pool of parental resources (Blake 1981;Hertwig et al. 2002) or sibling rivalry (Sulloway 1996). Sociologists and psychologists have also suggested that socialization processes or opportunity structures work differently in families of different sizes and that they may differ by birth order of the child (Dunn 2007;McHale et al. 2012). ...
... An important explanation for why earlier-born siblings cope better is that parents' resources (including non-economic resources such as time) are fixed, and consequently, having more children leads to fewer available resources per child (Blake 1989). This dilution of parental resources results in a cumulative advantage of earlier-born children over later-born children, and explains their favourable outcomes (Hertwig et al. 2002). Another explanation for birth order effects is Zajonc and Markus' (1975) confluence model of intellectual development. ...
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This study examines how the sibling constellation in childhood is associated with later fertility behaviour of men and women in Sweden. Administrative register data are used to investigate how birth order affects completed fertility, how the number of siblings and birth order jointly affect completed fertility, and in both cases if there are gender differences in these relationships. Our data consist of all fully biologically related siblings in Sweden whose mothers were born between 1915 and 1935 (the younger generation is born primarily in the 1940s, 1950s and 1960s; N = 1,472,813). To study the direct effect of birth order on fertility, sibling comparison models are applied, while to analyse the joint effect of number of siblings and birth order, the sample was stratified by birth order. Results show that higher birth order has a negative effect on completed fertility for women; hence, earlier-born women show overall higher fertility than later-born women. Parity transitions indicate that later-born women are less likely to have two or more children, while no overall gradient for men can be found. The number of siblings is more positively associated with completed fertility for firstborn than for later-born individuals. We conclude that the position in the family of origin can be seen as an additional factor that influences fertility, although effect sizes are rather small.
... Natural selection would therefore favour specific parental behavioural strategies aimed at maximizing fitness by investing more in children with greater productive value. In turn, parental favouritism depends on the perceived reproductive value of each child and invests in proportion to their expected fitness (Clarke & Low, 2001;Hertwig, Davis, & Sulloway, 2002;Veller, Haig, & Nowak, 2016). In addition, competition and rivalry among siblings, as well as parent-child conflicts, may be triggered and increased by differentials in parental care, and investments in offspring are also shaped by parental and household circumstances. ...
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This special section contains a collection of articles that study how children are affected by their sibship size and composition by examining their influence on several demographic outcomes across time and space. The importance of the specific historical context, as put forward by the conditional or gendered resource dilution model, seems to be justified, as inheritance practices and gender preferences were determining demographic outcomes.While these studies provide us with the possibility of reflecting on what kinds of pathways/mechanisms are behind sibling effects, they also demonstrate that much more can and should be investigated.Four recommendations for future studies are formulated: (1) future studies should continue on the same path as the articles in this special section and address different outcomes in a variety of contexts to determine under which conditions siblings matter for life transitions and demographic outcomes; (2) theoretical frameworks from different disciplines should be integrated to increase knowledge exchange; (3) researchers should think more about, and be transparent about, how siblings and families are defined; and (4) qualitative studies should be included to a greater extent, since quantitative studies alone cannot answer the questions we have about how and why sibling effects influence life transations and outcomes.
... Such parental resources are crucial for better educational outcomes of earlier born and vice versa. Regardless of whether we accept guardians who disseminate assets similarly among their kids, earlier-born are benefited more than later-born children 10 . Second, the Confluence hypothesis (Confluence model claims that the intellectual development within a family depends on cumulative intellectual environment where a first born enjoys rich cognitive stimulation as compared to latter born children) posits that the first born directly interacts with cognitively mature parents thus enhancing his chances of intelligence as compared to later born children who acquire a diluted intellectual environment 11 . ...
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We studied the effects of birth order and socioeconomic factors on educational attainment in Pakistan. We examined this relationship by using PSLM/HIES 2018–19 which is nationally representative household survey data. We found striking evidence that being born first as a male child is positively and significantly associated with educational attainment. Whereas in our girls' sample we found that being born first is significantly and negatively associated with educational attainment, and this effect does not persist for second-born female children if the firstborn is a male child. Such a difference in our estimates led us to investigate further the cohort and rural–urban dimensions. We concluded that urban areas in Pakistan are primarily responsible for resource rationing in favor of male children for younger cohorts. Therefore, the study recommends the targeted policy intervention to remove such differentials based on gender when it comes to the educational attainment of a child.
... In terms of accumulated parental resource since the birth of a child, the firstborn would receive the most attention, because there would be a period of time during which they enjoy undivided attention from their parents, in the absence of siblings, while the opposite could be said for the youngest child in the family who would have been born into a comparatively lower average share of parental resource. It could then be the case that in theory, the more older siblings a child has, the less they receive from their parents relatively, whether it be the resource on average at a point in time, or the cumulative investment throughout their formative years [54]. Evidence for this negative effect of higher birth order (meaning, having more older siblings) on children can be found in work by Black, Devereux and Salvanes [50], who have also pointed out that the negative effect applies regardless of the socioeconomic status of the household; although studies such as Steelman and Powell [53] suggested minor financial advantage later in life among younger siblings. ...
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Book reading is an important factor contributing to children’s cognitive development and education for sustainable development. However, in a developing country like Vietnam, statistics have reported a low figure in book reading: only 1.2 books a year. This research study used a dataset of 1676 observations of junior high school students from Northern Vietnam to explore students’ reading behavior and its association with demographic factors, and the family’s reading culture. Data analysis suggests the older the student gets, the less inclined they are to read, and being female and having hobbies of low sensory stimulation are linked to higher preference for reading. Regarding scholarly culture at home, students who read more varied types of books and spend more time on books are correlated with higher reading interest. Reading habits are also positively reinforced by the capacity to access books and parental book reading.
... From an evolutionary perspective, both theoretical and empirical studies have shown that parents do not express their feelings toward and invest in their children equally (Daly and Wilson, 1988). Although parents may attempt to invest in their children equally, the fact that investment in children is heterogeneous due to parental favoritism may affect the perceptions of favoritism (Hertwig et al., 2002). These parental perceptions are considered to be catalysts for different processes related to personality development among siblings, affecting their approach to dealing with family, friends, partners, and colleagues (Salmon and Schumann, 2011). ...
Article
The one-child policy was implemented in September 1980 and abolished in late 2015. With this change in the demographic policy, the fertility decision of families also changed. Such decisions can result in an increase in the number of siblings in a family. Individuals' educational outcomes may be affected by a change in their parents' fertility decision. The objective of this paper is to provide evidence of the difference of educational outcomes between the only-child and the non-only child. The authors try to estimate the change of educational outcomes when the only child of a family turns to the child with siblings. Moreover, they estimate different channels to interpret these effects. They employ the data set of China Education Panel data in this paper. In the part of mechanism check, the Sobel-Good test is used for checking the mediation effects of different channels. The authors found the only child has significant higher educational outcomes comparing to a child who has siblings. To explain these effects, the authors use four channels to interpret: (1) money resource, (2) parenting time, (3) closeness of parent-child relationships, and (4) personality traits. The policy implication is to help the policymaker estimate and predict the impact of new demographic policy.
... Parents' divisions of their resources among their children typically follow the equality norm. Parents tend to allocate their resources of affection, time, help, nurturing, and energy equally to their children (Hertwig et al. 2002). This may be due to the collapse of too complex rules differentiating each child, leading to one simple heuristic of treating ever child equally. ...
Article
While experimental game theory has provided evidence that social norms can promote cooperation, the importance of normative conflict has received little attention so far. We present results from an experiment on the dynamics of normative conflict over the consideration of equality, equity, or efficiency for the distribution of joint earnings. Normative conflict is measured by the number of rejected offers in a dynamic bargaining game. We find that more alternative normative principles lead to more persistent normative conflict. Furthermore, we show that, in either simple or complex situations, the convergence towards a simple and widely shared norm is likely. In contrast, in moderately complex situations, convergence is unlikely and several equally reasonable norms co-exist.
... This finding supports the present study finding that first-born children have better OHRQoL than their younger siblings. This may be attributed to the fact that first-born children, at some point, received all the care and attention from their parents medically, financially, and socially until their siblings were born into the family [39,40]. However, a significant association between the number and sequence of siblings and OHRQoL was not observed in children with CD. ...
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Purpose There is limited knowledge about oral health-related quality of life (OHRQoL) in children with celiac disease (CD). This study aimed to assess OHRQoL in children with CD compared to healthy controls. Methods This case–control study included children with CD and healthy controls. Three scales were used to assess OHRQoL in different age groups: 6–7 years, 8–10 years, and 11–14 years. The OHRQoL scores were compared between cases and controls to examine the possible associations between OHRQoL and demographics, socioeconomic status, and oral health. Results Overall, 104 children with CD and 104 healthy children (controls) were included. The mean age was 10.67 ± 2.39 years in CD patients and 10.69 ± 2.36 in controls (P = 0.971). Male and female children constituted 50% of each group. Children with CD had significantly higher OHRQoL scores than controls (P = 0.003). Low education levels of parents of children with CD and a higher number of siblings in controls were associated with high OHRQoL scores (P = 0.002, P < 0.020, and P = 0.010, respectively). Recurrent aphthous stomatitis (RAS) increased the OHRQoL scores by 7.5 on average (P = 0.016). Conclusion Children with CD had poor OHRQoL compared with healthy controls. Poor OHRQoL in children with CD was associated with RAS and with lower parental income and education. RAS was an independent predictor of poor OHRQoL in children with CD.
... In prior studies, mostly in the context of the United States, the negative influence of a large number of siblings is more widely recognized (Blake 1989;Steelman et al. 2002). As suggested by the resource-dilution model, more children might lead to fewer family investments in each child due to finite parental resources, especially for the later-born children (Blake 1981;Hertwig, Davis, and Sullnwav 2002). This is in line with the quantity-quality trade-off model developed by Gary Becker and his colleagues (Becker 1960(Becker , 1991Becker and Lewis 1973). ...
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Background: Most previous research on intergenerational impacts on childbearing behaviors has overlooked the interrelation between having siblings and the availability of childcare assistance provided by grandparents. Objective: This study examines how the siblings of young couples dilute the resources of grandparental childcare assistance and thus influence a mother’s plans to have a second child in urban China. Methods: We use data from the survey on Fertility Decision-Making Processes in Chinese Families conducted in 2016 and focus on the subsample of mothers who have only one child and live in urban areas. Results: The husband’s parents are less likely to take care of grandchildren if the husband has male siblings, while the probability will be higher if the wife has male siblings. The chance of receiving childcare support from the wife’s parents is also associated with the sibship status of both wife and husband. The results suggest that the decision regarding primary childcare providers might be made collectively within extended families. Under the two-child policy, childcare support from parents or in-laws in raising the first child increases the probability of a mother planning a second child. Furthermore, the positive effect of childcare support from the husband’s parents is lessened if the husband has siblings. Contribution: This article tests the resource-dilution model in adulthood by examining the association between grandparental childcare assistance and young couples’ sibship status. Siblings may compete for grandparental childcare support and thus reduce the positive influence of grandparental childcare assistance on a mother’s plans for another child.
... A similar relationship was also found between birth order and dental visits during adolescence 26 . Birth order may affect the amount of investment in children since, for many families, there are limited resources to divide among existing children, and cumulative investments (e.g., healthcare expenditure) are lower for later-born children 27 . However, this mechanism might not be suitable for explaining FDV among infants in Beijing, China, as only 1.2% of mothers reported that they did not take the child to a dentist because of high dental costs, indicating that dental costs are unlikely to be a barrier for young urban parents. ...
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Background The first dental visit (FDV) within 1 year of age is important for establishing good oral health behaviors for young children, but delayed FDVs are common. Aim This study aimed to investigate the predisposing, enabling, and need factors of maternal willingness to attend the FDV for infants. Design A cross-sectional survey was conducted among mothers of infants aged 11−14 months. A questionnaire was developed based on Andersen’s behavioral model of health service utilization. Data regarding the FDV, FDV willingness, and reasons for not attending the FDV were collected. Logistic regression models were used to investigate the associated factors. Results Of 658 infants, only 2.7% (18) had FDV. Thirty percent (191/640) of mothers reported their willingness to attend the FDV in the next 3 months. Nearly two-thirds of mothers reported not attending the FDV since their children’s teeth were healthy. Maternal perceptions of their infants’ oral health status were negatively associated with willingness to undergo the FDV, while family social support was positively associated with willingness to undergo the FDV. Conclusions Need factors play a key role in the utilization of FDV. Improving parental awareness of FDV might help parents voluntarily attend the FDV, and offering support from the family and healthcare system levels enables access to pediatric dental care.
... Further, differential parental investment in offspring might be masked by other possible factors. Parents do not equally offer their investment to multiple children (Daly and Wilson 1988), and empirical evidence suggests that the amount of parental investment differs depending on birth order (Buckles and Kolka 2014;Hertwig et al. 2002). However, there are other factors affecting differential parental investment. ...
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Considerable research has been performed on the association between sibling composition and various characteristics, including personality, intelligence, and social attitudes. These studies suggest that birth order among siblings could weakly but significantly affect the development of personality traits and intelligence. However, few studies on the association between sibling composition and moral foundations have been conducted. Therefore, the present study investigated whether sibling composition (only child, firstborn, laterborn) is related to moral values with a between-family design. A sample of 500 Japanese adults (250 women) completed the self-administered online questionnaire. The mean age was 45.42 years (SD = 8.53, range = 20–60, median = 46). The general linear model was used to test the association between sibling composition and moral values. The results showed no differences in five moral foundation and two higher-order moral dimension scores between firstborns and laterborns. However, only children scored lower on care/harm, fairness/cheating, and individualizing foundation than laterborns. This finding might indicate that growing up with their siblings positively affects the development of care/harm and fairness/cheating (individualizing foundation) regardless of one's position among those siblings.
... There may be some deviation from the precisely optimal strategy in the direction of a uniform attention split. A similar equity (aka 1/N ) heuristic has been documented in other allocation problems such as financial portfolio choice (Benartzi & Thaler, 2001) and parental effort investment (Hertwig, Davis, & Sulloway, 2002). In the former case, this bias toward naive diversification has been found to improve performance, potentially due to the way it approximately captures the principle of regularization or Bayesian shrinkage (Tu & Zhou, 2011). ...
Preprint
When different stimuli belong to the same category, learning about their attributes should be guided by this categorical structure. Here, we demonstrate how an adaptive response to attention constraints can bias learning toward shared qualities and away from individual differences. In three preregistered experiments using an information sampling paradigm with mousetracking, we find that people preferentially attend to information at the category level when idiosyncratic variation is low, when time constraints are more severe, and when the category contains more members. While attention is more diffuse across all information sources than predicted by Bayesian theory, there are signs of convergence toward this optimal benchmark with experience. Our results thus indicate a novel way in which a focus on categories can be driven by rational principles.
... As family psychologists aver, "we know that parents do not act in a void, but, rather, in part, respond to child behavior as do children respond to parent behavior" (Bryant et al., 2006, p. 152). From an evolutionary biology standpoint, parents invest resources in order to render their children more socially competitive, which in turn enables their children to successfully reproduce (Hertwig et al., 2002). However, there is considerable variation in how much resources parents invest in their children, particularly in adolescence (Suitor et al., 2008). ...
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Conventional wisdom views the parent-child relationship as unilateral: Parents' actions upstream flow downstream to shape their children's development. However, scholars have proposed that this view of parenting is lopsided; children may influence their parents no less than parents influence children. We apply this bilateral perspective in a reexamination of the robust finding that confident people report having had more supportive parents. The social-cognitive explanation for this finding is that parents endow their children with support that builds confidence. However, evolutionary accounts suggest that confident children-displaying more promise and potential-ought to attract their parents' investments of support. We examined these predictions in a four-wave longitudinal study drawing on both archival and field survey data from 350 STEM students (science, technology, engineering, and mathematics) in the Philippines. Results were consistent with the bilateral perspective, in which parental support endowed children with confidence, but also children's confidence attracted parental support in equal measure. These reciprocal relations also had implications for whether or not students persisted in their computer science degrees. The results indicate that parental endowments of confidence and parental investments of support form a virtuous cycle, consistent with the perspective that self-efficacy operates not only as an intrapsychic resource allocator but also as an interpersonal resource attractor. (PsycInfo Database Record (c) 2021 APA, all rights reserved).
... The effects are theoretically hard to predict as they may go in opposite directions. On the one hand, children may behave differently from their siblings in order to capture more parental attention (Hertwig, Davis & Sulloway, 2002;Sulloway, 1996). This is especially pronounced if siblings are of opposite gender (Feinberg, McHale, Crouter & Cumsille, 2003). ...
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This paper studies whether sibling gender affects personality traits. We use the idea that if parents decide to have a second child, it is random whether they will have a boy or a girl. Therefore, the relationship between the second-born sibling's gender and the first sibling's personality traits is causal. We employ longitudinal data from a large British cohort which is followed from birth onwards. The dataset includes personality traits at age 10 and 16. Our main result is that oldest boys in a household are more agreeable if their next-born sibling is a girl. This effect is robust across age (10 and 16), when controlling for among others family size, and when applying corrections for multiple hypothesis tests. Agreeableness is an important trait in life as it has been shown to correlate positively among others with being employed, having a skilled job, savings, and life satisfaction.
... This baseline evidence provides support to the unequal parental investment hypotheses predicting that firstborns receive more parental resources than laterborns, because, for instance, of their higher reproductive value or because they have been the only child in the household for a longer period (e.g. Hertwig et al. 2002). These preliminary results seem also consistent with economic theory of the family postulating a trade-off between quantity of the children (sibship size) and their quality (human capital, and in our case, trust in others). ...
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The renewed interest by the economic literature in the effect of birth order on children's outcomes has neglected trust as a long-term output of familial environment. Acknowledging childhood as a crucial stage of life for the formation of social preferences, we go deeper into the early-life determinants of trust, a widely recognized driver of socioeconomic success. We analyze if and how differences in the order of birth predict heterogeneous self-reported trust levels in Britain. We draw hypotheses from psychology, economics and sociology, and test alternative explanations to the association between birth order and trust. Relying on an index measuring birth order independently from sibship size, we find a negative and robust effect of birth order, with laterborns trusting less than their older siblings. This effect is not accounted for by personality traits, strength of family ties, risk aversion and parental inputs. It is only partially explained by complementary human-capital outcomes, and it is robust when we use alternative dependent variables and control for endogenous fertility. Multilevel estimates suggest that trust is mostly driven by within-rather than between-family characteristics. The effect of birth order is eclipsed by education outcomes only for women, while it is counterbalanced by mother's education for the entire sample, thereby leading to relevant policy implications.
... First-born children have been described as more likely to report high levels of parental control and influence (Ng, Mofrad, & Uba, 2014), with parental discipline weakening from first-born to last-born (Hotz & Pantano, 2015). Moreover, parents tend to engage in different parenting strategies with children of different birth order (Hotz & Pantano, 2015) and siblings receiving more parental attention are expected to have more positive emotions towards the family compared with siblings receiving less parental attention (Bu & Sulloway, 2016;Hertwig, Davis, & Sulloway, 2002). For the UK, Booth and Kee (2009) found that in the presence of more than one child, parents do not assign equal shares in the family's educational resources and that the amount of resources devoted to each child decreases with birth order. ...
Article
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Parental involvement in sex education and the quality of parent-child communication about romantic feelings appear to have a protective effect on adolescent sexual behaviours. However, little research has been conducted on the role played by birth order in the level of parental involvement in sex education. This is the first study seeking to address if the quality of parent-child communication about sex and romantic sentiments differs according to whether respondents have-or do not have-older siblings in Italy. Hypotheses concerning the role of sib-ship gender composition have been tested in order to explain potential intervening mechanisms. Data were drawn from the Sexual and Emotional Life of Youths survey (SELFY), a cross-sectional survey conducted in 2000 and in 2017 on Italian university students (N = 12,265). Our findings identify later-born children as the least likely to confide in parents. Although boys are generally less likely to talk to parents than girls, respondent gender does not moderate the effect of birth order. Instead, sib-ship gender composition plays a role: having grown up with at least one same-gender sibling is associated with a lower communication with parents about intimate matters. This study suggests that growing up with siblings, namely with same-gender siblings, make a difference in parent-child communication and this should be considered while evaluating the role of parental involvement in adolescent sexual education.
... We begin by presenting the two dominant theories of birth order. Both theories emphasize the importance of children living together or at least interacting frequently with both parents, competing for resources, tutoring each other, and so forth (Black et al. 2005;Hertwig et al. 2002). 1 ...
Article
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A substantial amount of research shows that younger siblings perform worse than their older sisters and brothers in several socioeconomic outcomes, including educational achievement. Most of these studies examined stable families and excluded half-siblings. However, the increasing prevalence of multipartnered fertility implies that many children grow up in nonnuclear families. We examine whether there is evidence for birth order effects in this context, which offers an opportunity to test and potentially expand the explanatory scope of the two main theories on birth order effects. We use comprehensive Norwegian registry data to study siblings in the 1985-1998 cohorts born to mothers or fathers who parented children with at least two partners. We provide evidence for negative effects of birth order on lower secondary school grades in both cases. Children born to fathers displaying multipartnered fertility tend to have lower grades than older full siblings but perform more similarly or better compared with older half-siblings. For siblings born to mothers with the multipartnered fertility pattern, later-born siblings do worse in school compared with all older siblings. This indicates that negative birth order effects tend to operate either within or across sets of full siblings, depending on the sex of the parent displaying multipartnered fertility. We argue that these findings can be explained by a combination of resource dilution/confluence theory and sex differences in residential arrangements following union dissolutions. We also suggest an alternative interpretation: maternal resources could be more important for generating negative birth order effects.
... However, it has been suggested that later born siblings have lower physical fitness in late adolescence than first born one [19]. This is usually more prominent in societies with high household size (5.6 persons per household in Gaza Strip) [17], where sharing the parental resources' pool among offspring is mostly unequal [20]. This could also be related to childhood exposure to poverty, under-education and child labour, which has been frequently suggested to be relevant to large size families [21], but with lack of sufficient evidence on its role on the fertility status of upgrowing individuals later in life. ...
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Introduction: The aim of this study was to address the relationship between housing and living conditions that couples might experience before and after marriage and primary infertility in Gaza Strip, Palestine. Methods: A case-control study of 160 infertile couples matched residentially with 160 fertile ones was per- formed in Gaza Strip, Palestine. Infertile couples were chosen from list of patients registered in five fertility centers from 2016 to 2018. Data was collected through a self-administered questionnaire and analyzed through SPSS program version 22 by using descriptive analysis, cross-tabulation, and binary logistic regres- sion. Results: A positive association between using private vendors as a source of drinking water before marriage and primary infertility (P < 0.001) was demonstrated in females and males. Being a refugee (P = 0.036), living near borders (P = 0.011), living in extended families (P = 0.021), paying for rents (P = 0.029), and using septic porous sewer tanks (P = 0.020) provided a positive significant relationship after marriage. Odds of drinking water from rooming tanks before marriage was seven times risk in females (95% Confidential Interval [CI] 1.44 to 32.52, P = 0.020) mostly ovulatory and idiopathic causes, using septic sewer porous tanks held three times risk (95% CI 1.33 to 6.92, P = 0.008) mostly obstructive and ovulatory causes in ma- les and females, respectively and living in extended families held twice risk (95% CI, 1.20-3.56, P = 0.009) mostly nonobstructive causes in males and ovulatory and endometrial causes in females. Conclusion: Our findings provided evidence for the effect of inadequate living conditions on the fertility status of both women and men which opens the gate for further in-depth randomized trials.
... Quando a família possui apenas um filho todo o investimento financeiro, de tempo e atenção, vai para ele. Se há dois filhos, o investimento aplicado a ambos tende a ser o mesmo, mas a idade da criança em que este investimento ocorre pode ser diferente (Hertwig, Davis & Sulloway, 2002). Contudo, em uma pesquisa recente, foi averiguado que o tipo de família, a estrutura familiar e a situação parental não são preditores do padrão de apego daquelas crianças (Simões, Farate, Soares & Duarte, 2013). ...
Article
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O estabelecimento de uma relação de apego segura é importante, pois fornece à criança segurança para que ela possa explorar o ambiente, atividade essencial para o desenvolvimento infantil. Este estudo tem como objetivo investigar se crianças com padrão de apego seguro e inseguro diferem quanto ao desempenho cognitivo, linguístico e motor. Participaram do estudo 50 crianças, com idades entre 12 e 25 meses. Foram utilizados um questionário de anamnese, a Situação Estranha de Ainsworth, as Escalas Bayley de Desenvolvimento Infantil – 3ª ed. e o questionário Estilo Materno como instrumentos de avaliação. Os resultados apontam diferença entre os grupos no desempenho cognitivo e de linguagem. Crianças com padrões inseguros de apego obtiveram menores escores nos testes que avaliam o desenvolvimento dos dois domínios. Estes resultados demonstram a importância da relação entre mãe e filho como um fator de proteção do desenvolvimento.
... Social scientists have examined the relation between birth order and various outcomes for more than a hundred years (Galton, 1874). Results of the conducted studies showed that the first-born children have tendency to reach more resource, attention and higher level of cognitive warnings (Hertwig, Davis, & Sulloway, 2002;Price, 2008). First-born child enters into interaction with parents alone and he/she is exposed to an environment with comparatively higher level of cognitive maturity. ...
Article
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There are many factors that may affect employees’ job performance such as psychological, sociological, anthropological, demographic and similar. However, related literature was mainly focusing on psychological and demographic ones, which were often analyzed through different job performance measurement methods such as self-evaluation and supervisor (or superior) evaluation. The main goal of the current study is to define and compare the factors affecting employee’s job performance according to the above mentioned measurement methods, as well as their level of importance. For the purpose of this study, data were collected through survey conducted in the Antalya region in Turkey among 305 participants coming from seven countries and consisting of both employees and supervisors working for a performing artists organization company. Data were analyzed by using CHAID analysis through classification algorithms. Results show there is a difference between variables explaining the job performance of the employees when they do self-evaluation of their own performance than when the same is done by their supervisors. In addition, when importance order of explaining variables was examined, it turns out that ranking varies according to the evaluator.
... Historically this translated into primogeniture practices. Although vestigial primogeniture practices may persist today, modern parents likely try to employ non-discriminatory strategies (Hertwig et al., 2002). However, despite parents' best efforts, the cumulative share of resources might still differ, placing firstborns in a favorable position at a critical stage, earlier in their development, which might trigger a snowball effect and eventually better educational outcomes (Price, 2008). ...
Article
We tested birth order effects on selection into different careers (scientific, artistic, and creative) and status attainment (educational attainment, occupational prestige, and income) using a large sample ( n = 3763), a longitudinal design, and relevant controls. Additionally, we tested mediation of birth order effects on career outcomes via personality traits, intelligence, and educational attainment. We found negligible birth order effects ranging from 0.02 to 0.12 on a correlational metric, where firstborns (vs. laterborns) selected into more creative careers and attained higher prestige and education. Conditional on the theoretically based mediation models tested, results showed that intelligence and educational attainment (but not personality traits) accounted for a statistically significant portion of the variance in the links between birth order and career outcomes. No direct effects of birth order on career outcomes remained when accounting for indirect effects through educational attainment. These findings bring modest support to the confluence model, no support to the niche-finding model, and suggest that one possible route via which birth order might impact career outcomes (if at all) could be via educational attainment.
... Social scientists have examined the relation between birth order and various outcomes for more than a hundred years (Galton, 1874). Results of the conducted studies showed that the first-born children have tendency to reach more resource, attention and higher level of cognitive warnings (Hertwig, Davis, & Sulloway, 2002;Price, 2008). First-born child enters into interaction with parents alone and he/she is exposed to an environment with comparatively higher level of cognitive maturity. ...
Article
Full-text available
There are many factors that may affect employees’ job performance such as psychological, sociological, anthropological, demographic and similar. However, related literature was mainly focusing on psychological and demographic ones, which were often analyzed through different job performance measurement methods such as self-evaluation and supervisor (or superior) evaluation. The main goal of the current study is to define and compare the factors affecting employee’s job performance according to the above mentioned measurement methods, as well as their level of importance. For the purpose of this study, data were collected through survey conducted in the Antalya region in Turkey among 305 participants coming from seven countries and consisting of both employees and supervisors working for a performing artists organization company. Data were analyzed by using CHAID analysis through classification algorithms. Results show there is a difference between variables explaining the job performance of the employees when they do self-evaluation of their own performance than when the same is done by their supervisors. Nationality is one of the factors affecting performance in both evaluation forms. While the performance of individuals with extraversion personality traits was high in case of self-evaluation, the performance of the men who were second-born or after was high in the evaluation by the supervisors. These results demonstrated the problematic nature of measuring job performance and making accurate evaluations based on it.
... Puer and Serrano (1973) have shown that laterborns generally have higher mortality rate in various Latin American countries. This has also been documented in developed countries (Hertwig et al. 2002). This leads to laterborns to incur in more risks, as the costs of risk taking are reduced whenever life expectancy is reduced (Daly and Wilson 1988) (Wang et al. 2009). ...
Article
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Several studies have shown that birth order and the sex of siblings may have an influence on individual behavioral traits. In particular, it has been found that second brothers (of older male siblings) tend to have more disciplinary problems. If this is the case, this should also be shown in contact sports. To assess this hypothesis we use a data set from the South Rugby Union (URS) from the region of Bahía Blanca, Argentina, and information obtained by surveying more than four hundred players of that league. We find a statistically significant positive relation between being a secondborn male rugby player with an older male brother and the number of yellow cards received.
... These factors may be particularly pronounced in families with greater number of children and may explain why middle-born individuals were more likely to have PE compared to the first-born only among those with a large number of siblings. The finding that lastborn individuals were not at an increased risk for PE maybe reflecting the fact that first-born and last-born children are better positioned to receive parental resources at the expense of middle-born siblings (Hertwig et al., 2002). ...
Article
Background Sibship size and birth order may be contributing factors to the multifactorial etiology of psychosis. Specifically, several studies have shown that sibship size and birth order are associated with schizophrenia. However, there are no studies on their association with psychotic experiences (PE). Methods Cross-sectional, community-based data from 43 low- and middle-income countries which participated in the World Health Survey were analyzed. The Composite International Diagnostic Interview was used to identify four types of past 12-month PE. The association of sibship size and birth order with PE was assessed with multivariable logistic regression. Results The final sample consisted of 212,920 adults [mean (SD) age 38.1 (16.0) years; 50.7% females]. In the multivariable analysis, compared to individuals with no siblings, the OR increased linearly from 1.26 (95%CI = 1.01–1.56) to 1.72 (95%CI = 1.41–2.09) among those with 1 and ≥ 9 siblings, respectively. Compared to the first-born, middle-born individuals were more likely to have PE when having a very high number of siblings (i.e. ≥9). Conclusions Future studies should examine the environmental and biological factors underlying the association between sibship size/birth order and PE. Specifically, it may be important to examine the unmeasured factors, such as childhood infections and adversities that may be related to both family structure and PE.
... As such, care needs to be exercised in extrapolating the current findings to other decision strategies. While we chose these two strategies because of their suitability for the current research setting, future research could test additional strategies, such as take-the-best (Gigerenzer & Goldstein, 1996), the recognition heuristic (Gigerenzer & Goldstein, 2011), the 1/N heuristic (Hertwig, Davis, & Sulloway, 2002), and more sophisticated machine learning algorithms. ...
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This research presents new evidence on the negative associations of the number of siblings and birth order with years of schooling among female and male Spanish cohorts born in the first six decades of the twentieth century. Special attention is given to unravelling the separate effects of both factors, sib size and birth order. Based on data from the 1991 Spanish Sociodemographic Survey (SDS), findings in Spain support the theoretical framework of the family conditional resource dilution model and indicate that both number of siblings and birth order have been important and relatively independent factors in reducing educational attainment. The association of family size and birth order with educational attainment was contingent to a significant extent on socio-economic status. Whereas the educational consequences of number of siblings are not uniformly distributed by social class, the results for birth order are much more homogeneous. This suggests that parents in high socioeconomic statuses were able to limit the effects of dilution induced by the number of siblings while the dynamics of the dilution of resources associated with the birth order depended, in part, on factors not entirely controllable by families.
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The article analyses theoretical approaches and empirical research of the influence of the children’s birth order in the family on their intellectual and creative abilities, achievements in education, personality traits, behaviors and social preferences. It is shown that the results of the studies vary depending on the method of data analysis - the effect of decreasing intelligence while increasing the birth sequence number detected when comparing indicators of large numbers of children with different birth order from different families, and generally not detectable in intra-family analysis data. To explain the differences obtained the authors used three basic theoretical models: a model of merge, the model of resource depletion and impurity model. Due to differences in birth order personality traits have more pronounced differences in the cognitive sphere. Research confirms that according to the results of the personal questionnaire «Big five» firstborns display more pronounced «honesty», and younger children-«kindness» and «openness» to experience. Individual work on features of social interaction of senior and subsequent children demonstrated a great ability of younger children to cooperation. Despite the fact that the prognostic significance of identified effects in large samples is not as great as in individual families, results may have practical significance for the pedagogical and psychological work with children.
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Ancient monuments are puzzling from an evolutionary perspective. It is obvious that their construction would have been costly in terms of energy, but it is not clear how they would have enhanced reproductive success. In the late 1980s, Robert Dunnell proposed a solution to this conundrum. He argued that wasting energy on monuments and other forms of what he called “cultural elaboration” was adaptive in highly variable environments. Here, we report a study in which we used an agent-based model to test Dunnell’s hypothesis. We found that the propensity to waste was subject to strong negative selection regardless of the level of environmental variability. At the start of the simulation runs, agents wasted ca. 50% of the time but selection rapidly drove that rate down, ultimately settling at ca. 5–7%. This casts doubt on the ability of Dunnell’s hypothesis to explain instances of cultural elaboration in the archaeological record.
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Economic and evolutionary models of parental investment often predict education biases toward earlier-born children, resulting from either household resource dilution or parental preference. Previous research, however, has not always found these predicted biases—perhaps because in societies where children work, older children are more efficient at household tasks and substitute for younger children, whose time can then be allocated to school. The role of labor substitution in determining children’s schooling remains uncertain, however, because few studies have simultaneously considered intrahousehold variation in both children’s education and work. Here, we investigate the influence of coresident children on education, work, and leisure in northwestern Tanzania, using detailed time use data collected from multiple children per household (n = 1,273). We find that age order (relative age, compared with coresident children) within the household is associated with children’s time allocation, but these patterns differ by gender. Relatively young girls do less work, have more leisure time, and have greater odds of school enrollment than older girls. We suggest that this results from labor substitution: older girls are more efficient workers, freeing younger girls’ time for education and leisure. Conversely, relatively older boys have the highest odds of school enrollment among coresident boys, possibly reflecting traditional norms regarding household work allocation and age hierarchies. Gender is also important in household work allocation: boys who coreside with more girls do fewer household chores. We conclude that considering children as both producers and consumers is critical to understanding intrahousehold variation in children’s schooling and work.
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Acknowledging childhood as a crucial period for the formation of social preferences, we investigate whether the order of birth predicts trust in adult life. We find that laterborns trust on average 5% less than their older siblings, independently from personality traits, family ties, risk aversion and parental inputs. Family random- and fixed-effects estimates suggest that the variation in trust is mostly explained by within- rather than between-family characteristics. The effect of birth order is mediated by education outcomes only for women, while it is moderated by mother’s education for the entire sample, thereby leading to relevant policy implications.
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Kin terms such as "brothers," "sisters," and "motherland" are frequently used in both political and patriotic speech. Johnson (1986, 1987) has argued that this use of kin terms in patriotic or rhetorical speech can be predicted on the basis of evolutionary psychology. He has suggested that the human inclination toward nepotistic behavior can be called forth by the successful manipulation of kin terminology. In this study, two hypotheses were examined concerning the evocativeness of kin terminology in political speech and the influence of birth order on the effectiveness of such terminology. The first hypothesis was that kin terms would be more effective than more distant relationship terms (like "friend") in evoking a positive response. Kin terms elevated agreement with the views expressed in the speech that the subjects heard. The second hypothesis, that middleborns would be less likely to respond to such kin term usage than first or lastborns, was based on previous work on birth order and family relations (Salmon and Daly, in press). And in fact, middleborns were less likely to be influenced by the use of kin terms than first or lastborns in this study.
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Although the inverse relationship between the number of siblings and children's educational performance has been well established, explanations for this relationship remain primitive. One explanation, resource dilution, posits that parents have finite levels of resources (time, energy, money, etc.) and that these resources are diluted among children as sibship size increases. I provide a more rigorous investigation of the dilution model than previous studies, testing its implications with a sample of 24,599 eighth graders from the 1988 National Education Longitudinal Study. My analyses support the resource dilution model in three ways. First, the availability of parental resources decreases as the number of siblings increases, net of controls. The functional form of this relationship is not always linear, however, and depends on whether the resource is interpersonal or economic. Second, parental resources explain most or all of the inverse relationship between sibship size and educational outcomes. Finally, interactions between sibship size and parental resources support the dilution model as children benefit less from certain parental resources when they have many versus few siblings.
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We tested various predictions based on Sulloway's (Born to rebel: birth order, family dynamics, and creative lives. New York: Pantheon, 1996) theory of family relations, using questionnaires completed by 2024 participants from Austria, Germany, Israel, Norway, Russia, and Spain, each of whom had at least one sibling. The parents' most favored child tended to be the lastborn sibling. The rebel of the family tended to be a laterborn, and rebels tended to feel less close to their parents. In sibships of two, firstborns named a parent as the person to whom they were closest more often than did lastborns; in sibships of three or more, middleborns were the least likely to name their mother, but were more likely than firstborns and lastborns to name their father or a sibling. However, these quadratic effects on closeness to parents occurred only in sibships in which mothers were relatively old at the time of participant's birth. Sex differences, but not birth order differences, were found in the tendency to choose parents for emotional support, with women scoring higher than men. Our study demonstrates the robustness of birth order differences in samples from diverse countries and emphasizes that these
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Although theories of parental investment and sex ratio generally assume that a single resource limits reproduction, many organisms invest two or more qualitatively different types of resources in the production of offspring. We examine the consequences of multifaceted parental investment for offspring provisioning and sex allocation, building our argument around a study of the nest-building Hymenoptera (wasps, bees, and ants). We review empirical studies that demonstrate that lifetime reproductive success may be constrained not only by resources used to provision offspring but also by the supply of mature oocytes or, in some cases, by the availability of space within nest sites or the time required to defend nests. Under multifaceted parental investment, the factor limiting parental fitness determines the currency of the optimization problem; parents are predicted to adjust reproductive behavior to maximize fitness returns per unit of the limiting resource. We develop simple models that predict that a greater availability of resources used for provisions will lead to an increase in the amount provisioned per offspring and an increase in the numerical or biomass proportion of females produced. These predictions explain widely observed patterns of variation in offspring provisioning and sex allocation in the nest-building Hymenoptera.
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We investigated birth order effects on personality and achievement in four studies (N = 1,022 families) including both stu- dent and adult samples. Control over a wide range of variables was effected by collecting within-family data: Participants compared their siblings (and themselves) on a variety of personality and achievement dimensions. Across four diverse data sets, first-borns were nominated as most achieving and most conscientious. Later-borns were nominat- ed as most rebellious, liberal, and agreeable. The same results obtained whether or not birth order was made salient (to activate stereotypes) during the personality ratings. Overall, the results sup- port predictions from Sulloway's niche model of personality develop- ment, as well as Zajonc's confluence model of intellectual achievement.
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Effects of birth order on several aspects of family relations and self-identity were examined in three studies. In Study 1, first and lastborn undergraduates were more likely than middleborns to refer to kinship in characterizing themselves. In Study 2, subjects were asked to whom they would turn under two scenarios of duress. First and lastborns were more likely to nominate parents, whereas middleborns were much more likely than other respondents to nominate siblings. In Study 3, analyses of historical archives and of an Internet questionnaire indicated that genealogical research attracts many more firstborns and many fewer middleborns than expected by chance. In all three studies, first and lastborns were much more likely than middleborns to nominate their mothers as the person to whom they felt closest. These substantial effects support Sulloway's claim that birth orders constitute significant family "niches," which differ with respect to the perceived dependability of parental investment and therefore also differ in the social orientations that they engender.
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A detailed account of the !Kung San of northern Botswana. Drawing on the theoretical traditions of cultural ecology, historical materialism and ecological systems theory, applies the evidence of fieldwork to the historical evolution of the group structure, subsistence technology, nutrition, land use, control of violence and socioeconomic transformations central to !Kung San life. -Jennifer Clayton
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This study was conducted to determine whether a relationship exists between birth order and academic self-concept. While previous studies have not consistently given evidence for such a relationship, it has been suggested that birth-order effects might be related to time of measurement and general cultural milieu. For a sample of 2116 children, academic self-concept was highest among boys but not girls who were only children. It was also generally higher among girls than boys, and generally lower among middle-born than among younger or oldest children. Also evidence indicated academic self-concept declines with age. These findings are discussed, in part, relative to time of measurement.
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This study examines the effect of the sibling structures of number and spacing, sex composition, and birth order on adolescents' perceptions of the power and support dimensions of parental behavior. These sibling structures are conceptualized as dimensions on a hypothetical sibling time line, including number of siblings and the way in which they are arranged in time, i.e., the spacing and birth order. Data were obtained from a secondary analysis of a national sample of over 1,700 adolescent males. The results suggest that research focusing on birth order as an explanatory variable must control for number of siblings, spacing, and sex composition of siblings; studies examining family size must control for sibling spacing, birth order, and sex composition. In addition a curvilinear relationship was found between perceived parent behaviors and wider spacing between siblings. The "best" spacings are the widest (five years) and the narrowest (one year or less), with spacings of two and three years being the most negative. Most of the power in the curvilinear relationship obtains with male respondents whose closest sibling is male. Males whose closest sibling is female, however, view their parents as more punitive. Both empirical and practical implications of these findings are discussed.
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The prevailing assumption of analysts of relationships between infant mortality and fertility is that high fertility is a necessary biological and behavioral response to high mortality. Mortality, however, may sometimes be a response to high fertility instead of a stimulus to it. In some societies, infant mortality resulting from underinvestment in some children may be an unconscious or even an overt way of attaining a given family size. Anthropological evidence indicates the presence of deliberate control of both fertility and mortality in primitive and preindustrial societies. Evidence of avoidable infant mortality in contemporary societies suggests possible linkages to fertility levels.
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We investigate the influence of size of sibling group and ordinal position on financial arrangements for college. While this analysis has implications for the status attainment and human capital perspectives, it also represents a direct test of the resource dilution hypothesis. Analyzing a sample of 3279 subjects from the National Longitudinal Survey of the High School Class of 1972, we estimate the association between the number of siblings and (1) the likelihood of parental support of students in college, (2) the amount of parental contributions, and (3) the proportion of total college costs borne by parents. In all cases, a strong inverse relationship is found. Conversely, large sibship sizes increase the dependence upon funds from extrafamilial sources, such as loans, scholarships, employment, and savings. Effects of birth order, although less pronounced, signify a financial advantage to latter-born children. Moreover, sibship structure affects the likelihood that youths cite financial barriers for not attending college.
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This study examines the self-esteem of middleborns compared with firstborns and lastborns. While most of the birth-order research concentrates on comparing firstborns with a general category of "laterborns," the present research emphasizes an empirical and conceptual distinction for middleborns. The number, spacing, and sex of siblings of the middleborn are also closely examined. Data were obtained from a secondary analysis of a national sample of over 2,200 adolescent males. The results suggest that middleborns have a significantly lower self-esteem than firstborns and lastborns and that the self-esteem of middleborns is significantly lower when the average spacing of their immediately adjacent siblings is two years compared with one year. Self-esteem of the middleborn male is significantly enhanced when his siblings are all female than when they are all male or mixed gender. The findings are explained according to a uniqueness theory, which suggests that firstborns and lastborns enjoy an inherent uniqueness in their birth order which facilitates status, recognition, and attention by parents and other siblings. There is no inherent uniqueness in the position of middleborn child, whose role in the family is consequently less well defined. This is reflected in the middleborn's overall self-assessment.
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Using a unique data source on family time use both in and outside the home, we obtained estimates of parental time allocated to preschool children for several socioeconomic status groups. We find that while high status mothers have a relatively high potential wage, they spend from two to three times as much time in preschool child care as do low status mothers. To the extent that this class differential in time investments to preschool children influences cognitive achievement, our results indicate again that equal educational programs across different school systems need not imply equal educational opportunity.
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Although sociologists have identified factors associated with the timing of births, little is known about the consequences of the spacing of births. Several perspectives imply a negative effect of close spacing of siblings on educational attainment, but these perspectives differ in the mechanisms used to explain this effect. We use data from the High School and Beyond survey to investigate the effect of spacing on high school attrition and post-secondary school attendance. Our analysis confirms that close spacing increases the likelihood of dropping out of high school and decreases the odds of attending post-secondary school. The direct effect of close spacing on post-secondary school attendance persists net of ability and academic performance; the effect of spacing on dropping out of high school is mixed. Close spacing of siblings also constrains the allocation of family resources, which in turn affects educational attainment. Alternative explanations of the relationship between sibship structure and educational outcomes are reinterpreted in light of these findings.
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Why are individuals from the same family often no more similar in personality than those from different families? Why, within the same family, do some children conform to authority whereas others rebel? The family, it turns out, is not a "shared environment" but rather a set of niches that provide siblings with different outlooks. At the heart of this pioneering inquiry into human development is a fundamental insight: that the personalities of siblings vary because they adopt different strategies in the universal quest for parental favor. Frank J. Sulloway's most important finding is that eldest children identify with parents and authority, and support the status quo, whereas younger children rebel against it. Drawing on the work of Darwin and the new science of evolutionary psychology, he transforms our understanding of personality development and its origins in family dynamics.
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313 pairs of brothers and 296 pairs of sisters were compared by one or both parents in a postal questionnaire. For 495 pairs independent questionnaires were completed by father and mother, and agreement between parents was good. There was a marked tendency for the first-born child to be rated as less fond of cuddling; he was also easier to train, worked harder at school, set himself higher standards, and was more serious, methodical, law-abiding, tidy and less impulsive; he learned to talk and read at a younger age and was rated as having more natural ability at schoolwork. These three groups of first-born attributes were relatively independent; for instance, even the first-born with less ability at schoolwork were given more responsibility at school. In the 152 pairs which did not contain a first-born, little birth order effect could be found, whether or not the elder was the eldest of his or her sex. There was a slight tendency for the broader, fatter and more muscular child to be less nervous and highly strung, but otherwise differences in physique were not related to differences in behaviour. Abilities at schoolwork, games, music and painting were not related. Tendency to anxiety and depression was related to lack of sociability; to stubbornness and lack of practicality; to angryness but not the bottling up of anger; to level of aspiration but not the possession of abilities or good looks. These relations of anxiety and depression in a normal sample closely parallel the items which distinguish psychiatric patients from their healthy siblings.
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Recent articles have argued that family size and birth order have important cognitive influence, and may partially explain the different performances of social class and ethnic groups. Support for such claims has often depended on the analytic strategy, which has concentrated on the means of aggregated groups with large N’s. For the present analysis, data are reviewed from the massive U. S. National Longitudinal Study of Educational Effects. Results from aggregate analysis are quite similar to those reported by Zajonc and others. When individual variation is explored, however, the effects of family configuration become relatively trivial, and the confluence theory appears untenable. The apparent effects of family size, far from explaining population differences, seem themselves to be better explained as the result of group admixtures. And the small, residual birth-order effects therefore appear to result from other phenomena, still to be explained.
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To document alloparenting among the 18 Efe camps of the Ituri Forest in the northeastern Democratic Republic of Congo data were collected between January 1988 and October 1989. The focal subject sampling technique was adapted to record the behaviors of infant and mother simultaneously across all contexts. Systematic and informal interviews were conducted with mothers and other caregivers. The study included discussions on a logistic regression model of the occurrence of allocare and linear regression model of the amount of time spent in allocare. Comparisons between individuals in allocaregiving time regression fit to hypothesized allocaregivers reciprocity and resource exchange and cost of alloparenting were included as well. The data shows consistency with analyses of Efe care of young infants and older children. Child rearing among the Efe demonstrates the central role of human life history and social ecology in providing the opportunity for multiple modes of cooperation in parenting. The modes would include nepotism reciprocity and learning-to- mother. The study further reveals that the life history and ecology of the Efe hold clues that productive and reproductive constraints facilitate allocare by affecting the access that individuals have to food and social security.
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Although sibship size has become a standard measure in the study of academic achievement and attainment, logical and theoretically meaningful extensions of this variable often have been ignored. Sex composition--the number of brothers and the number of sisters--is one such extension. This article reports on a study of the impact of sex composition on strategies for funding a college education. Data on 454 seniors at two large universities confirm that the number of brothers poses a greater obstacle than does the number of sisters to parents' financial support of their children's college education. In addition, the alternative means by which students fund their college education are more strongly affected by the number of brothers than by the number of sisters they have. The authors conclude that sex composition of sibship strongly merits inclusion in educational research.
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A previous study of sibling deidentification in undergraduates was cross-validated on a new population, mothers judging pairs of their own children; at a new age level, averaging 6.4 years; and using same-opposite as well as alike-different judgments. The design also included a developmental study. Judgments of 95 mothers with 2 children and 45 with 3 cross-validate previous findings. (1) Percentage deidentification was significantly higher for first pairs (first 2 children) than jump pairs (first and third children), with intermediate levels for second pairs (second and third children). (2) Deidentification was higher for same-than opposite-sex siblings among first pairs. (3) Global judgments covary with semantic differential polarization scores. Developmental analysis indicates a linear increment until age 6, when deidentification stabilizes at extremely high levels for first pairs. Opposite and different judgments covary. Results support the hypothesis that deidentification is a defense against sibling rivalry, although an alternative explanation, that mothers impose deidentification on their children, merits consideration.
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Past studies linking schooling and career attainment to sibling position (family size, birth order, spacing) are vulnerable to suspicions about omitted variables: being based on cross-sections of individuals from different families, they may have attributed to sibling position an influence belonging to unobserved parental attributes. This study retests the link between sibling position and achievement, using a cross-section of intrafamily sibling differences. The alleged link is confirmed. Further, its pattern is very consistent with the view that sibling position matters because of its straight-forward effects on family time and commodity inputs into children.
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Equality rule is often used heuristically in resource allocation. The functioning of such an equality heuristic was examined in bargaining situations where two persons negotiated how to share a common cost or how to share a common benefit between them. Based on Prospect Theory (Kahneman & Tversky, 1979), it was predicted that equality heuristic would have a smaller anchoring effect on bargaining outcomes in cost-sharing than in benefit-sharing. The results of two experiments confirmed this prediction, revealing that deviation of the bargaining outcomes from equal-splitting of overall amount was actually larger in cost-sharing than in benefit-sharing. Other behavioral patterns during negotiation were also consistent with the prediction. Implications of these findings for the “demand revelation” context (Samuelson, 1954) were discussed, where negotiators have no reliable information about other person's demand/contribution level.
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A model is presented that shows that reduced fertility in humans can be explained as part of an evolved strategy to maximize long-term fitness in the face of periodic calamities that result in demographic crashes. Three conditions must be met for this model to be plausible: (1) human population history has been characterized by local periods of growth punctuated by recurrent crashes caused by calamities such as climatically induced resource shortfalls; (2) a strategy is available to individuals that increases the probability of survival through a crash, but that, to implement, requires diverting resources away from producing more offspring; and (3) long-term fitness benefits to increased survivorship through a crisis must outweigh or equal the fitness benefits that would accrue to putting the same resources into higher fertility. We present a model that shows that increases in survivorship can outweigh the benefits of higher fertility even if crises are neither very frequent nor particularly severe.
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The Ache, whose life history the authors recounts, are a small indigenous population of hunters and gatherers living in the neotropical rainforest of eastern Paraguay. This is part exemplary ethnography of the Ache and in larger part uses this population to make a signal contribution to human evolutionary ecology.
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This paper critiques the literature on the relationship between sibling structure and academic abilities and achievement since Cicirelli’s (1978) earlier commentary on this topic. Assessed is the extent to which the confluence model, a theoretical explanation of the influence of sibling structure, fits the empirical observations made recently on the association between sibship structure and intellectual development. Since the studies reviewed in general tend to refute the confluence model, alternative interpretations of the impact of sibling structure on academic consequences are presented. Implications for future research are also provided.