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Parental Investment and Sexual Selection

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Robert Trivers at Chapman University
Robert Trivers
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Trivers 19
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All content in this area was uploaded by Robert Trivers on Jul 24, 2017
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... The most well-investigated variable to account for variance in mate preferences is whether someone is a man or a woman which is unsurprising given the recurrent asymmetries in reproductive investment in the sexes (Trivers, 1972). One of the most fundamental concerns for humans is that their offspring are helpless for an extended period which requires substantial parental investment. ...
... One of the most fundamental concerns for humans is that their offspring are helpless for an extended period which requires substantial parental investment. While modern welfare systems may protect single mothers today, the need for a warm, resourceful, and good partner in parenting originates from ancestral pressures (Trivers, 1972). Because the minimum necessary investment in reproduction is higher for women (and female mammals), we would expect they will want a partner who is warm and has high resource acquisition potential such as high status and dominance more than how important it is for men (Jonason & Thomas, 2022;Jonason et al., 2012). ...
... In older age, both men and women preferred more creative and domestic partners (Schwarz & Hassebrauck, 2012). Lastly, online dating studies suggested that while men became more demanding in their preferences with age, women lowered their expectations (De Sousa Campos et al., 2002). 1 In contrast to sex differences in mate preferences, there is less work on sex differences in mate aversions, but the evidence does align with parental investment theory (Trivers, 1972). From this perspective, the sex that pays heavier costs for mating mistakes will have stronger and more sensitive rejection systems. ...
Observed Aspects of Mate Value and Sociosexuality Account for Mate Preferences: Data from a Large, Representative Study from Czechia
Article
Full-text available
While there is substantial research on what people want in their romantic and sexual partners, much of this work focuses on WEIRD, youthful samples, fails to consider the role of undesirable characteristics (i.e., things people do not want in partners) at all, or in conjunction with desirable characteristics (i.e., things people do want in partners), and may be overly reliant on psychometric approaches to pivotal variables in mating psychology like mate value and sociosexuality. In a nationally representative (online) sample of 2280 people from Czechia (aged between 18 and 50 years old), we examined linear and quadratic age, education, and self-perceived mate value (desirability) effects on the desired levels in mate choice of eight undesirable and seven desirable characteristics in men and women in relation to ostensible metrics of mate value. Self-perceived mate value alone explained little variance (men 1%, women 2%), while all mate value and mating strategy indicators together explained little variance of mate preferences and aversions (men 3%, women 5%). Desirable characteristics were better explained by mate value than undesirable ones. Our results are in line with evolutionary predictions suggesting that women are more demanding. Also, more qualities to offer correlate with more expectations in a partner.
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... This impacts the classic theories because they are built on the assumption that ageing evolved under natural selection. However, unlike natural selection which results from differential fecundity and survival, sexual selection is the outcome of variance in mating/ fertilization success (Trivers 1985;Rowe and Rundle 2021). Typically the strength of sexual selection is stronger in males than females (Borgia 1985;Emlen et al. 2005;Clutton-Brock 2007;Dakin and Montgomerie 2013). ...
... Typically the strength of sexual selection is stronger in males than females (Borgia 1985;Emlen et al. 2005;Clutton-Brock 2007;Dakin and Montgomerie 2013). Moreover, in certain organism's males invest less in generating offspring than females (Trivers 2017). In theory this means males can direct additional resources to attracting females. ...
The evolution of ageing: classic theories and emerging ideas
Article
Full-text available
  • Oct 2024
  • BIOGERONTOLOGY
Ageing is generally regarded as a non-adaptive by-product of evolution. Based on this premise three classic evolutionary theories of ageing have been proposed. These theories have dominated the literature for several decades. Despite their individual nuances, the common thread which unites them is that they posit that ageing results from a decline in the intensity of natural selection with chronological age. Empirical evidence has been identified which supports each theory. However, a consensus remains to be fully established as to which theory best accounts for the evolution of ageing. A consequence of this uncertainty are counter arguments which advocate for alternative theoretical frameworks, such as those which propose an adaptive origin for ageing, senescence, or death. Given this backdrop, this review has several aims. Firstly, to briefly discuss the classic evolutionary theories. Secondly, to evaluate how evolutionary forces beyond a monotonic decrease in natural selection can affect the evolution of ageing. Thirdly, to examine alternatives to the classic theories. Finally, to introduce a pluralistic interpretation of the evolution of ageing. The basis of this pluralistic theoretical framework is the recognition that certain evolutionary ideas will be more appropriate depending on the organism, its ecological context, and its life history.
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... Mass weddings have contributed to the improved status of women, as the government has assisted single mothers and their families in overcoming poverty (Ejaz, 2006). Trivers (2000) concluded that, despite the significance of other institutions, the family remains the cornerstone of society, owing to its longstanding role in providing for its members. Marriage establishes the institution of a family, and a person's marital status is indicative of the cultural group to which they belong. ...
Cultural Significance Unveiled: Exploring the Dynamics and Influences of Traditional Dowry Practices in Pakistan
Article
Full-text available
  • Dec 2023
Aim of the Study: Pakistan, like other South Asian countries, upholds the longstanding tradition of providing a dowry to the bride's family. A dowry comprises money, valuables, or gifts that the bride gives to the husband as a wedding offering. It encompasses the items provided by the bride's parents in preparation for her marriage. It's important to note that a dowry is not mandated by Islam, and the inclusion of money as part of a dowry is not customary. At times, a dowry may include a year's supply of groceries, clothing for a year and ten to fifteen gowns for the wife. In recent times, it seems that women may expect larger dowries due to evolving societal norms. Regrettably, the practice of dowry, widely considered undesirable, still prevails in Pakistan. The purpose of this study is to explore the perspectives of both men and women on dowry, its impact, its necessity, and how it adversely affects women's rights and autonomy. Methodology: A self-designed interview schedule was employed to gather qualitative data from a diverse group of participants from urban and rural communities, including Chakwal, Arifwala, Chichawatni, Islamabad, and Jhang. This sample encompassed individuals with varying socioeconomic backgrounds and educational levels, aged between 18 and 45. A total of thirty-one interviews were conducted, with ten involving male participants and eleven involving female participants. The interviews followed a purposive sampling approach. Findings & Conclusion: It is a common view among Pakistanis that the practice of paying a dowry is no longer widely accepted; it is often seen as a trend, with individuals using it as a way to express appreciation for their mothers and other female role models. The positive connotation of these intangible items supports the notion that in Pakistan, dowry is a trousseau freely given by the bride's parents to their daughter. Furthermore, the practice of paying a dowry is deeply flawed and should be universally banned. It serves as a major catalyst for conflicts, avarice, and even societal unrest. A dowry is essentially a form of inheritance that parents bestow upon their daughters. Those who can provide substantial dowries for their daughters are more likely to facilitate their marriage.
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... Despite their early autonomy, the calves kept seeking contact with their mothers presumably because of their nutritional dependence, whereas mothers showed little effort in maintaining proximity from the first month after parturition and during all studied months postpartum. While mothers may limit their parental care to optimize their fitness and production of future offspring (Trivers, 1972(Trivers, , 1974, such avoidance behaviour may also relate to the parenteoffspring conflict (Trivers, 1974). In this context, mothers may attempt to reduce maternal care and keep a distance from their calves, whereas calves may seek contact for as long as possible for nursing and protection benefits (Chen et al., 2018;Nielsen et al., 2019;Szabo & Duffus, 2008;Taber & Thomas, 1982;Tardin et al., 2013). ...
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... In the second stage, as brain-size increase continued or was renewed, ritual displays were organized irrespective of whether any coalition member was menstruating, rewarding investor males. With males having to work harder to gain reproductive access, they would be choosier about which females to invest in, with the corollary of inter-female competition (Trivers 1972;Gowaty 1997). Power (2009) proposed that female cosmetic coalitions would, in the second stage, be indexically advertising the coalitionary support available to any offspring born into that coalition, while simultaneously stabilizing the transmission mechanism of a communal realm of pretend-playextended from childhood to adulthood through ritual. ...
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... In addition, Z&A demographic data can help tackle fundamental challenges in understanding sex-based differences in ageing [26] (see also Chapter 9,Lemaître et al.). First, males and females of the same species are expected to show different ageing and longevity, which is notably due to differences in trade-offs between reproduction and somatic maintenance following the sex-specific actions of the natural and sexual selection [27]. Second, across vertebrates, it has been hypothesised that species with intense male mating competition and high levels of sexual dimorphism in body size exhibit dimorphism in age-specific reproductive success [28]. ...
The Untapped Potential of Zoo and Aquarium Data for the Comparative Biology of Ageing
Chapter
  • Nov 2024
Why and how we age are probably two of science's oldest questions, echoing personal beliefs and concerns about our own finitude. From the earliest musings of ancient philosophers to recent pharmacological trials aimed at slowing ageing and prolonging longevity, these questions have fascinated scientists across time and fields of research. Taking advantage of the natural diversity of ageing trajectories, within and across species, this interdisciplinary volume provides a comprehensive view of the recent advances in ageing and longevity through a biodemographic approach. It includes the key facts, theories, ongoing fields of investigation, big questions, and new avenues for research in ageing and longevity, as well as considerations on how extending longevity integrates into the social and environmental challenges that our society faces. This is a useful resource for students and researchers curious to unravel the mysteries of longevity and ageing, from their origins to their consequences, across species, space and time.
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... Irrespective of the proximate mechanisms, age-related differences in chemical composition of lizard scent marks can have significant functional implications, as they can be detected by conspecifics and influence on species closely related to P. erhardii have demonstrated that oleic acid can elicit strong chemosensory responses (Cooper et al., 2002) and that females can discriminate between males of different age classes based solely on the scent of their secretions (Martín & López, 2013;Nisa Ramiro et al., 2019). This ability allows female Iberolacerta cyreni lizards to actively choose their preferred older mates (López et al., 2003), whose longevity attests to their viability (Kokko, 1998;Trivers, 1972). Note that López et al. (2003) did not account for body size in their analyses, which may conflate the effects of size and age. ...
Temporal dynamics of scent mark composition in field‐experimental lizard populations
Article
Full-text available
Animal signals are dynamic traits that can undergo considerable spatial and temporal changes and that are influenced by factors such as age, health condition and interactions with both the abiotic and biotic environment. However, much of our understanding of signal changes throughout an individual's lifetime stems from cross‐sectional, often laboratory‐based, studies focused on visual and auditory signals. Longitudinal field investigations of temporal variation in chemical signals, especially in vertebrates, remain rare despite chemical communication being the most ubiquitous form of information exchange in the natural world. To remedy this, we conducted a unique, replicated field experiment to study the temporal signal dynamics in free‐living lizard populations on natural islands. Specifically, we collected scent marks from individually marked lizards across five populations during the spring of two consecutive years and analysed the lipophilic chemical composition of these scent marks. Our findings demonstrate that the overall scent mark composition of individual lizards changed over time, shifting consistently in both direction and magnitude from year to year among individuals and across replicate populations. Similar patterns were observed for the chemical richness and diversity of scent marks. Temporal variation in the relative proportions of three potentially socially relevant signalling compounds in lizard scent marks revealed a more complex pattern: α‐tocopherol remained stable over time, oleic acid decreased and the change in octadecanoic acid proportion was body size‐dependent. Together, our results provide novel insights into how individual vertebrate chemical signals may fluctuate across space and time. We discuss the potential causes of the observed temporal variability and its consequences for chemical signal evolution. Read the free Plain Language Summary for this article on the Journal blog.
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Aversive sexual learning in the kissing bug Rhodnius prolixus: Modulation of different sexual responses in males and females
Article
Full-text available
  • Dec 2024
  • J INSECT PHYSIOL
Although sexual learning can be a key process in the reproductive success of animals, research focused on the experience-dependent modulation of courtship in insects is scarce. In kissing bugs, the behavioural steps implicated in mating have been exhaustively studied, but not the involvement of learning in them. Our objective was to determine whether the sexual behaviour of Rhodnius prolixus could be modulated by experience. During training, couples were submitted to eight assays, in which they received a vibration (negative reinforcement) when the male attempted to copulate the female. Immediately after, they were separated, not allowing the occurrence of copulation. We found that along training, males’ latency to perform a copulatory attempt increased, male’s copulatory attempts were less frequent, and females’ locomotor activity did not change. These results suggest that males, and not females, learned to avoid the vibration by reducing their intention to copulate. In post-training tests, conditioned males presented with new naïve females reverted to low copulatory attempt latencies, suggesting that the modulation was partner-specific. Besides, conditioned females increased their rejection frequencies to males’ copulatory attempts, suggesting that a second type of learning occurred in females. These results constitute the first evidence of sexual learning in hematophagous insects. Males and females seem to change their selectivity according to their previous sexual experience. We discuss the relevance that this plasticity might have in the fitness of this epidemiologically relevant insect.
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Linking proximate drivers and fitness returns of vigilance in a large ungulate
Article
Full-text available
  • Nov 2024
Vigilance allows animals to quickly detect threats from conspecifics and predators to avoid or minimize costly encounters. Time spent vigilant is usually traded‐off against other fitness‐enhancing activities, such that fitness returns are expected when allocation to vigilance increases. We assessed the proximate factors influencing vigilance and investigated whether vigilance correlates with fitness in wild mountain goats. We first studied which extrinsic and intrinsic factors influenced alert duration and frequency using focal observations recorded over 12 years on individually‐marked adult females. We found that females increased vigilance in forested areas compared with open areas and were less vigilant when they were surrounded by conspecific neighbours. Reproductive females were more frequently vigilant and for longer periods compared with females without offspring. Mothers also tended to perform longer alerts when their offspring was > 10 m away than at shorter distances, suggesting that variation in offspring's vulnerability to predation influences mother's vigilance. Thus, predation risk and offspring vulnerability were the main mechanisms driving variation in vigilance. To assess fitness returns, we then used a joint modelling framework to estimate the latent correlations at the individual level among vigilance traits (alert duration, alert frequency, and total time spent vigilant) and fitness components (adult female survival and offspring survival) while accounting for the drivers observed to influence vigilance. Contrary to expectations, we found no evidence that vigilance is associated with fitness returns, with only some traits being at best weakly positively correlated with survival of offspring and adult females. This might arise because vigilance incurs costs that outweighs its potential benefits, or because vigilance metrics are not repeatable due to their high plasticity, challenging the commonly assumed positive relationship between vigilance and fitness.
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Measuring behavioral synchronization and spatial cohesion in the activity budgets of three adult white-handed gibbon (Hylobates lar) dyads in Huai Kha Khaeng Wildlife Sanctuary, Thailand
Article
  • Oct 2024
  • FOLIA PRIMATOL
Individual behavior of primates living in small groups is often seen to represent behavior of all group members due to close spatial cohesion. However, given that females expend more energy on reproduction than males (including lactation and infant carrying), females and males may exhibit different behaviors even when maintaining spatial proximity, particularly in highly seasonal or resource-poor environments. We collected 187 hours of data from three dyads (n = 6 individuals) of white-handed gibbons ( Hylobates lar ) living in a fruit-poor environment in western Thailand during the period of fruit scarcity. We calculated activity budgets, dyad behavioral synchronization, and dyad spatial cohesion. We hypothesized that activity budgets would differ significantly between sexes or pairs would engage in behaviors independently to provide females with an opportunity to obtain more resources. We also hypothesized that pairs would remain in close proximity. Overall, activity budgets exhibited significant variation when analyzed by sex ( X ² = 27.693, ) and group ( X ² = 119.584, ). Females spent less time resting and vocalizing and more time traveling compared to males. Percentages of synchronized behavior were lower than expected with only 55% of records synchronized (group B: 58.6%; group D: 58.5%; group L: 49.7%). Spatial cohesion, however, was relatively high overall with adults in the same or adjacent trees in 67.1% of paired records but significantly variable across groups (B: 89.4%; D: 73.1%; L: 48.2%; X ² = 190.111, ). We suggest that behavioral synchronization and spatial cohesion may be indicators of pair bond strength, not just the result of pair living. Given differences in activity budgets, low behavioral synchronization, and variable amounts of time pair mates spent apart, we conclude that pair mates should be considered individual actors who engage in behaviors independently from one another, particularly when coping with challenging ecological conditions.
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