Robert Trivers

Robert Trivers
Crafoord Laureate
Chapman University

PhD Biology Harvard 1972

About

99
Publications
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39,848
Citations
Introduction
The evolutionary genetics of honour killings (w/ Amy Jacobson) Only long-term study of fluctuating asymmetry and 2nd:4th digit ratio in humans (Jamaican Symmetry Project)—24 years and counting (w/ John Manning, Bernhard Fink and Gordon Getty)

Publications

Publications (99)
Article
Deception is used by plants, animals, and humans to increase their fitness by persuading others of false beliefs that benefit the self, thereby creating evolutionary pressure to detect deception and avoid providing such unearned benefits to others. Self-deception can disrupt detection efforts by eliminating cognitive load and idiosyncratic deceptiv...
Article
Digit ratio (2D:4D) – a proxy for prenatal sex steroids – shows sex, nationality and ethnic differences and is linked to pubertal onset. It is unclear whether right-left 2D:4D (Dr-l) also correlates with prenatal sex steroids, as evidence of these differences has been less conclusive. The present study examined the effects of sex, nation, ethnicity...
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This is a brief history of my intellectual life from age 13 to 29 years—and beyond. It encompasses mathematics, US history, and evolutionary biology, especially social theory based on natural selection.
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Digit ratio-a putative measure of prenatal sex steroids-may be related to body mass index (BMI). However, reports of correlations between 2D:4D and BMI have yielded mixed results with some studies showing no relationship while others have reported positive associations in men or women only. This study considers associations between self-reported 2D...
Article
Income inequality is associated positively with disease prevalence and mortality. Digit ratio (2D:4D)-a negative proxy for prenatal testosterone and a positive correlate of prenatal oestrogen-is related to several diseases. This study examined the association of income inequality (operationalized as relative parental income) and children's 2D:4D. P...
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Transgendered belief—the conviction that one is the opposite gender to one’s natal gender—may be influenced by prenatal sex steroids. We consider this possibility by examining the relationship between digit ratio (2D:4D—a suggested correlate of fetal testosterone and estrogen), natal gender, felt gender, and transsexual drug therapy in a large onli...
Article
Background Digit ratio (2D:4D) from soft-tissue measurements of fingers from children and adults from Black and White ethnic groups show sex differences (males<females) and group differences (Black< White). However, less is known about such differences in radiographic 2D:4D. Aim To consider sex and ethnic differences in radiographic 2D:4D of child...
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The role that physical attractiveness and fluctuating asymmetry (FA), a measure of developmental instability, play in self-perception and peer associations were explored in a well-studied cohort of Jamaican children using a novel research paradigm where subjects were already known to each other for extensive periods of time. The results showed that...
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Experimental modes of attacking malaria via mosquitoes will be described and analysed.
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Research on association between digit ratio (2D:4D; a putative correlate of prenatal sex steroids) and mental masculinity/femininity (Masc/Fem) has reported mixed findings. This may be due to differences in protocols for assessing 2D:4D and Masc/Fem across studies. Here, we consider the relationship between direct self-measured 2D:4D and occupation...
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It has been suggested that intergroup conflict has played an important role in the evolution of human cooperation—aggression against out-groups and cooperation with in-groups may be linked in humans. Previous research suggests that religion may help to facilitate this effect, such that those who view religion as a way to achieve non-religious goals...
Article
Self-deception is both commonplace and costly, which raises the question of what purpose it might serve. According to the dominant explanation in psychology and economics, self-deception is an intrapersonal process that fortifies and protects the self from threatening information. An alternative possibility is that self-deception evolved as an inte...
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Fluctuating asymmetry (FA), random deviation from perfect bilateral symmetry, is an indicator of developmental stability. Examining the ontogeny of FA can illustrate whether symmetry is actively maintained as the organism grows or breaks down as perturbations accumulate with age. Previous studies of changes in human FA with age have been cross-sect...
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Four studies and a computer simulation tested the hypothesis that people who are overconfident in their self-assessments may be more successful in attracting mates. In Study 1, overconfident people were perceived as more confident in their dating profiles, and this perceived confidence predicted increased romantic desirability. Study 2 revealed tha...
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Handedness is controlled by many genetic variants, some of which are in sex-dependent genes that also influence body asymmetry. One such asymmetry may be in foot length. Levy and Levy (1978) reported that right-handed males have longer right feet than left and left-handed males have longer left feet than right, while this trend was found to be reve...
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In a study of degree of lower body symmetry in 73 elite Jamaican track and field athletes we show that both their knees and ankles (but not their feet) are-on average-significantly more symmetrical than those of 116 similarly aged controls from the rural Jamaican countryside. Within the elite athletes, events ranged from the 100 to the 800 m, and k...
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Gender inequality varies across nations, where such inequality is defined as the disproportionate representation of one sex over the other in desirable social, economic, and biological roles (typically male over female). Thus in Norway, 40% of parliamentarians are women, in the USA 17%, and in Saudi Arabia 0%. Some of this variation is associated w...
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Objectives Body symmetry and physical strength in males have been related to aspects of mate “quality”—women seem to prefer men who display both “good genes” (as indexed by high symmetry/developmental health) and fighting ability (as indexed by physical strength). Here we show that fluctuating asymmetry (FA) of the body and physical strength are ne...
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Older adults favor emotionally positive material over emotionally negative material in information processing. Given the potentially harmful consequences of avoiding negative information, this aging positivity effect may provide benefits that offset its costs. To test this possibility, we assessed positivity in recall and blood indicators of immune...
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Suicide attacks and terrorism are characterized by cognitive simplicity, which is related to self-deception. In justifying violence in pursuit of ideologically and/or politically driven commitment, people with high religious commitment may be particularly prone to mechanisms of self-deception. Related megalomania and glorious self-perception are ty...
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A reanalysis of “Dance reveals symmetry especially in young men” (Brown et al. (2005) Nature, 438, 1148-1150.) failed to support most of the results of the paper, which was recently retracted. We briefly review this case and draw attention to a monograph that describes the evidence for scientific misconduct in considerable detail.
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Jamaican athletes are prominent in sprint running but the reasons for their success are not clear. Here we consider the possibility that symmetry, particularly symmetry of the legs, in Jamaican children is linked to high sprinting speed in adults. Our study population was a cohort of 288 rural children, mean age 8.2 (±1 SD = 1.7) years in 1996. Sym...
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Dear Editor, We write to point out that digit ratio may be a useful childhood biomarker for endurance running in adults. We have considered this question in a cohort of Jamaican children who have been studied from 1996 to the present day (Trivers et al. 1999). Digit ratio (2D:4D; the relative lengths of the second and fourth digits) is a negative c...
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The ratio of second to fourth digit length (2D:4D) is a correlate of prenatal testosterone. High 2D:4D is associated with low prenatal testosterone, and reduced sensitivity to testosterone. Klinefelter's syndrome (KS; 47 XXY) affects the endocrine system, such that low testosterone levels are found in KS foetuses, new-borns and adults. To date, the...
Data
a b s t r a c t How does self-deception affect the appreciation of humor and laughter? Fifty-nine undergraduates at Rutgers University (33 females, 26 males) were videotaped while watching a stand-up comedian for 28 min. Positive emotional expressions associated with laughter were analyzed for short sections of the act (total: 8 min or 14,400 video...
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Commentators raised 10 major questions with regard to self-deception: Are dual representations necessary? Does self-deception serve intrapersonal goals? What forces shape self-deception? Are there cultural differences in self-deception? What is the self? Does self-deception have costs? How well do people detect deception? Are self-deceivers lying?...
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In this article we argue that self-deception evolved to facilitate interpersonal deception by allowing people to avoid the cues to conscious deception that might reveal deceptive intent. Self-deception has two additional advantages: It eliminates the costly cognitive load that is typically associated with deceiving, and it can minimize retribution...
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We analyze the prevalence of B chromosomes in 1,601 species of orthopteran insects where chromosome number and shape are known. B chromosomes have been reported in 191 of these species. Bs are not uniformly distributed among orthopteran superfamilies, with evident hotspots in the Pyrgomorphoidea (32.3% of species carrying Bs), Grylloidea (14.9%), A...
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Deception is a universal feature of life, at all levels and in all relationships both within species and between species, inside individuals and outside, with strong effects on both deceiver and deceived. Being detected often results in a sharp reversal of fortune for the deceiver thereby intensifying selection to deceive successfully. In encounter...
Article
I went into evolutionary biology because I became convinced in 1965 that the foundation for psychology and social theory more generally should, and could, be based on the theory of natural selection. In 1964, a senior-year course at Harvard in psychology convinced me that that discipline was nowhere near putting itself together as a unified science...
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The Ultimatum Game (UG) measures cooperative tendencies in humans. A proposer offers to split a given sum of money between self and a responder, who may accept or reject the offer. If accepted, each receives the proposed split; if rejected, nobody receives anything. We studied the effect of the putative responder’s degree of facial symmetry (fluctu...
Book
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A thorough reanalysis of Brown et al. (2005) “Dance reveals symmetry especially in young men” shows that all of the major results appear to be based on hidden procedures designed to produce the results later derived. These procedures include the pre-selection of animations of Jamaicans dancing, apparently based on preliminary evaluation in New Jers...
Article
The ultimatum game measures cooperative tendencies in humans under experimental conditions. One individual can split money between oneself and another, while the other has the option of accepting or rejecting the offer, with each player receiving the accepted split or nothing if the split is rejected. We studied the association of players' degree o...
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It has been hypothesised that the ratio between the length of the 2nd and 4th digits (2D:4D) is a correlate of prenatal sex steroids, and this relationship is strongest for the right hand. Furthermore, it has been suggested that 2D:4D is sexually dimorphic, the dimorphism is determined early, and 2D:4D among children is stable with growth. Here, we...
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Dance is believed to be important in the courtship of a variety of species, including humans, but nothing is known about what dance reveals about the underlying phenotypic--or genotypic--quality of the dancer. One measure of quality in evolutionary studies is the degree of bodily symmetry (fluctuating asymmetry, FA), because it measures development...
Article
We determined whether supernumerary B chromosomes were nonrandomly distributed among major angiosperm lineages and among lineages within families, as well as the identity of lineages with unusually high B-chromosome frequencies (hot spots). The incidence of B chromosomes for each taxon was gathered from databases showing species with and without th...
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The ratio between the length of the 2nd or index finger and the 4th or ring finger (2D:4D) differs between the sexes, such that males have lower 2D:4D than females, and shows considerable ethnic differences, with low values found in Black populations. It has been suggested that the sex difference in 2D:4D arises early in development and that finger...
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In the UK and Japan, both men and women prefer somewhat feminised opposite-sex faces, especially when choosing a long-term partner. Such faces are perceived as more honest, caring, and sensitive; traits that may be associated with successful male parental investment. By contrast, women prefer less feminised faces for short-term relationships and wh...
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Genetic and Cultural Evolution of Cooperation. Peter Hammerstein, Ed. MIT Press, Cambridge, MA, 2003. 499 pp. $45, £29.95. ISBN 0-262-08326-4. In this volume, which grew out of a Dahlem Workshop, researchers from a wide range of fields--including biology, anthropology, economics, mathematics, political science, primatology, and psychology--discuss...
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The chromosomes of mammals tend to be either mostly acrocentric (having one long arm) or mostly bi-armed, with few species having intermediate karyotypes. The theory of centromeric drive suggests that this observation reflects a bias during female meiosis, favouring either more centromeres or fewer, and that the direction of this bias changes frequ...
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B chromosomes are extra chromosomes found in some, but not all, individuals within a species, often maintained by giving themselves an advantage in transmission, i.e. they drive. Here we show that the presence of B chromosomes correlates to and varies strongly and positively with total genome size (excluding the Bs and corrected for ploidy) both at...
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In this review we look at the broad picture of how B chromosomes are distributed across a wide range of species. We review recent studies of the factors associated with the presence of Bs across species, and provide new analyses with updated data and additional variables. The major obstacle facing comparative studies of B chromosome distribution is...
Data
We review studies of drive and the phenotypic effects of B chromosomes, focusing on the sex in which drive and phenotypic effects occur. We found information on drive and/or effects of Bs in 172 species, using R.N. Jones’ database of B research through 1994, updated by computer searches through 2003. Most species show drive (n=81) in contrast to dr...
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There is evidence that the ratio of the length of the 2nd and 4th digit (2D:4D) is negatively related to prenatal and adult concentrations of testosterone. It has also been reported that high levels of testosterone at conception in both fathers and mothers are associated with an increased sex ratio (proportion of males at birth). It follows from th...
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A collection of my top papers published just before 15 years work with Austin Burt on Genes in Conflict 2006, over 1000 citations itself
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The ratio between the length of the 2nd and 4th digit (2D:4D) is sexually dimorphic, with mean male 2D:4D lower than mean female 2D:4D. It recently was suggested that 2D:4D is negatively correlated with prenatal testosterone and positively correlated with prenatal estrogen. It is argued that high prenatal testosterone and low estrogen (indicated by...
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An evolutionary theory of self-deception-the active misrepresentation of reality to the conscious mind-suggests that there may be multiple sources of self-deception in our own species, with important interactions between them. Self-deception (along with internal conflict and fragmentation) may serve to improve deception of others; this may include...
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Testosterone, particularly prenatal testosterone, has been implicated in the aetiology of many extragenital sexually dimorphic traits. It is difficult to test directly for the effect of prenatal testosterone in humans. However, Manning, Scutt, Wilson, and Lewis-Jones (1998b) have recently shown that the ratio of the length of the 2nd and 4th digits...
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Fluctuating asymmetry, small deviations from perfect bilateral symmetry, is negatively correlated with health and positively correlated with sexual selection in human adults, but the accumulation, persistence, and fitness implications of asymmetries during childhood are largely unknown. Here, we introduce the Jamaican Symmetry Project, a long-term...
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Yu and Shepard have reported a preference for heavy women with high waist-to-hip ratios (WHR) in a culturally isolated population in southeast Peru. Their findings are interesting because a preference for low WHR is widespread in westernized populations. However, we disagree with their argument that cultural invariance is necessary for an adaptioni...
Article
Genomic imprinting refers to parent-specific gene expression, that is, to a difference in gene expression depending on which parent contributed the gene. In the usual case, an allele is silent when inherited from one parent while the identical stretch of DNA would be active were it inherited from the other, but sometimes this effect is seen in some...
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The expression pattern of genes in mammals and plants can depend upon the parent from which the gene was inherited, evidence for a mechanism of parent-specific genomic imprinting. Kinship considerations are likely to be important in the natural selection of many such genes, because coefficients of relatedness will usually differ between maternally...
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In many species, some individuals carry one or more B chromosomes: extra, or supernumerary chromosomes not part of the normal complement. In most well-studied cases, Bs lower the fitness of their carrier and persist in populations only because of accumulation mechanisms analogous to meiotic drive. It has been suggested that such genomic parasites a...
Article
Women and girls tend to cradle infants and dolls on the left side of the body. Left-sided cradling is found in chimpanzees and gorillas, is cross-cultural and present in historical works of art, and is transmitted down the human maternal line. One explanation for the left-cradling tendency is that it facilitates the flow of affective information fr...
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Trivers1 has suggested that where genetic or developmental constraints on the expression of a trait prevent male and female fitnesses from being maximized simultaneously, female mating preferences should evolve to favour males who exhibit variants of the trait that confer relatively low fitness on males but relatively high fitness on females. This...
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Graham Bell's review of indirect evidence suggesting parasite load as a key selective factor
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1. The social behavior of A. garmani was studied for a total of eight months during seven separate visits to a study area of nine acres in Jamaica. 2. Adult males are 2.25 times larger by weight than adult females. At all times of the year and at all sizes for which there are data males grow faster than females. Growth rates for the same individual...
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Halminton (1) was apparently the first to appreciate that the synthesis of Mendelian genetics with Darwin's theory of natural selection had profound implications for social theory. In particular, insofar as almost all social behavior is either selfish or altruistic (or has such effects), genetical reasoning suggests that an individual's social beha...
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When parent-offspring relations in sexually reproducing species are viewed from the standpoint of the offspring as well as the parent, conflict is seen to be an expected feature of such relations. In particular, parent and offspring are expected to disagree over how long the period of parental investment should last, over the amount of parental inv...
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Theory and data suggest that a male in good condition at the end of the period of parental investment is expected to outreproduce a sister in similar condition, while she is expected to outreproduce him if both are in poor condition. Accordingly, natural selection should favor parental ability to adjust the sex ratio of offspring produced according...
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A model is presented to account for the natural selection of what is termed reciprocally altruistic behavior. The model shows how selection can operate against the cheater (non-reciprocator) in the system. Three instances of altruistic behavior are discussed, the evolution of which the model can explain: (1) behavior involved in cleaning symbioses;...