Selection
Noel Johnson & John Nye
Journal of Economic Behavior & Organization, forthcoming
Abstract:
Why do seemingly irrational superstitions persist? We analyze the widely held belief among Asians that children born in the Year of the Dragon are superior. We use pooled cross section data from the U.S. Current Population Survey to show that Asian immigrants to the United States born in the 1976 year of the Dragon are more educated than comparable immigrants from non-Dragon years. In contrast, no such educational effect is noticeable for Dragon-year children in the general U.S. population. We also provide evidence that Asian mothers of Dragon year babies are more educated, richer, and slightly older than Asian mothers of non-Dragon year children. This suggests that belief in the greater superiority of Dragon-year children is self-fulfilling since the demographic characteristics associated with parents who are more willing and able to adjust their birthing strategies to have Dragon children are also correlated with greater investment in their human capital.
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Jacob Moorad, Daniel Promislow, Ken Smith & Michael Wade
Evolution and Human Behavior, forthcoming
Abstract:
Sexual selection, or competition among members of one sex for reproductive access to the other, is one of the strongest and fastest evolutionary processes. Comparative studies support the prediction that sexual selection is stronger in polygamous than in monogamous species. We report the first study of the effect on sexual selection of a change in mating system, from polygyny to monogamy, within a historical human population. Here we show that over the reproductive lifetimes of Utahns born between 1830 and 1894, socially induced reductions in the rate and degree of polygamy correspond to a 58% reduction in the strength of sexual selection. Polygyny conferred a strong advantage to male fitness as well as a weak disadvantage to female fitness. In contrast, mating with multiple males provided little benefit to females in this population. Polygamy benefitted males by increasing reproductive rates and by lengthening reproductive tenure. Each advantage contributed to roughly half of the increased total lifetime reproductive success. This study illustrates both the potency of sexual selection in polygynous human populations and the dramatic influence that short-term societal changes can have on evolutionary processes.
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Correlated genotypes in friendship networks
James Fowler, Jaime Settle & Nicholas Christakis
Proceedings of the National Academy of Sciences, forthcoming
Abstract:
It is well known that humans tend to associate with other humans who have similar characteristics, but it is unclear whether this tendency has consequences for the distribution of genotypes in a population. Although geneticists have shown that populations tend to stratify genetically, this process results from geographic sorting or assortative mating, and it is unknown whether genotypes may be correlated as a consequence of nonreproductive associations or other processes. Here, we study six available genotypes from the National Longitudinal Study of Adolescent Health to test for genetic similarity between friends. Maps of the friendship networks show clustering of genotypes and, after we apply strict controls for population stratification, the results show that one genotype is positively correlated (homophily) and one genotype is negatively correlated (heterophily). A replication study in an independent sample from the Framingham Heart Study verifies that DRD2 exhibits significant homophily and that CYP2A6 exhibits significant heterophily. These unique results show that homophily and heterophily obtain on a genetic (indeed, an allelic) level, which has implications for the study of population genetics and social behavior. In particular, the results suggest that association tests should include friends' genes and that theories of evolution should take into account the fact that humans might, in some sense, be metagenomic with respect to the humans around them.
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Andrea Camperio Ciani & Claudio Capiluppi
European Journal of Personality, January/February 2011, Pages 53-64
Abstract:
Whether personality differences exist between populations is a controversial question. Even though such differences can be measured, it is still not clear whether they are due to individual phenotypic responses to the environment or whether they have a genetic influence. In a population survey we compared the personality traits of inhabitants of an Italian archipelago (the three Egadi islands; N = 622) with those of the closest mainland population (Trapani area; N = 106) and we found that personality differences between small populations can be detected. Islanders scored significantly lower on the personality traits of openness to experience and extraversion and higher on conscientiousness. We suggest that these personality trait differences could be an adaptive response to a confined socio-environmental niche, genetically produced by a strong, non-random gene flow in the last 20-25 generations, rather than the flexible response of islanders to environmental variables. To test this hypothesis, we compared subsets of the islander population classified by ancestry, birthplace, immigration and emigration and found that differences in extraversion can be accounted for by gene flow, while openness to experience and conscientiousness can also be accounted for by some gene-environment interactions. We propose a Personality Gene Flow hypothesis suggesting that, in small isolated communities, whenever there is strong, non-random emigration, paired with weak and random immigration, we can expect rapid genetic personality change within the population.
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A Genome-Wide Analysis of Liberal and Conservative Political Attitudes
Peter Hatemi et al.
Journal of Politics, January 2011, Pages 271-285
Abstract:
The assumption that the transmission of social behaviors and political preferences is purely cultural has been challenged repeatedly over the last 40 years by the combined evidence of large studies of adult twins and their relatives, adoption studies, and twins reared apart. Variance components and path modeling analyses using data from extended families quantified the overall genetic influence on political attitudes, but few studies have attempted to localize the parts of the genome which accounted for the heritability estimates found for political preferences. Here, we present the first genome-wide analysis of Conservative-Liberal attitudes from a sample of 13,000 respondents whose DNA was collected in conjunction with a 50-item sociopolitical attitude questionnaire. Several significant linkage peaks were identified and potential candidate genes discussed.
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Muscularity and attractiveness as predictors of human egalitarianism
Michael Price, Jinsheng Kang, James Dunn & Sian Hopkins
Personality and Individual Differences, forthcoming
Abstract:
In ancestral human environments, muscularity and height (in males) and physical attractiveness (in both sexes) would theoretically have correlated positively with one's social status, and thus with one's ability to benefit from social inequality. We therefore hypothesized that individuals who are more characterized by these traits would be less egalitarian (i.e., less likely to believe that resources should be distributed equally in social groups). We used a white-light 3D body scanner to extract anthropometric measurements from 118 participants, and our four egalitarianism measures included social dominance orientation and social value orientation. We found that as hypothesized, muscularity and waist-chest ratio in males, and self-perceived attractiveness in both sexes, tended to associate significantly in the predicted directions with the four egalitarianism measures; most of these correlations were of medium size. Neither height, nor two anthropometrically-assessed attractiveness measures (volume height index and waist-hip ratio), associated significantly with any egalitarianism measure in either sex. Egalitarianism has crucial social repercussions (e.g., taxes, welfare and civil rights), and results from the current study shed light on its origins.
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Food availability at birth limited reproductive success in historical humans
Ian Rickard et al.
Ecology, December 2010, Pages 3515-3525
Abstract:
Environmental conditions in early life can profoundly affect individual development and have consequences for reproductive success. Limited food availability may be one of the reasons for this, but direct evidence linking variation in early-life nutrition to reproductive performance in adulthood in natural populations is sparse. We combined historical agricultural data with detailed demographic church records to investigate the effect of food availability around the time of birth on the reproductive success of 927 men and women born in 18th-century Finland. Our study population exhibits natural mortality and fertility rates typical of many preindustrial societies, and individuals experienced differing access to resources due to social stratification. We found that among both men and women born into landless families (i.e., with low access to resources), marital prospects, probability of reproduction, and offspring viability were all positively related to local crop yield during the birth year. Such effects were generally absent among those born into landowning families. Among landless individuals born when yields of the two main crops, rye and barley, were both below median, only 50% of adult males and 55% of adult females gained any reproductive success in their lifetime, whereas 97% and 95% of those born when both yields were above the median did so. Our results suggest that maternal investment in offspring in prenatal or early postnatal life may have profound implications for the evolutionary fitness of human offspring, particularly among those for which resources are more limiting. Our study adds support to the idea that early nutrition can limit reproductive success in natural animal populations, and provides the most direct evidence to date that this process applies to humans.
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Charles Raison, Christopher Lowry, Graham Rook
Archives of General Psychiatry, December 2010, Pages 1211-1224
Context: Inflammation is increasingly recognized as contributing to the pathogenesis of major depressive disorder (MDD), even in individuals who are otherwise medically healthy. Most studies in search of sources for this increased inflammation have focused on factors such as psychosocial stress and obesity that are known to activate inflammatory processes and increase the risk for depression. However, MDD may be so prevalent in the modern world not just because proinflammatory factors are widespread, but also because we have lost contact with previously available sources of anti-inflammatory, immunoregulatory signaling.
Objective: To examine evidence that disruptions in coevolved relationships with a variety of tolerogenic microorganisms that were previously ubiquitous in soil, food, and the gut, but that are largely missing from industrialized societies, may contribute to increasing rates of MDD in the modern world.
Data Sources: Relevant studies were identified using PubMed and Ovid MEDLINE.
Study Selection: Included were laboratory animal and human studies relevant to immune functioning, the hygiene hypothesis, and major depressive disorder identified via PubMed and Ovid MEDLINE searches.
Data Extraction: Studies were reviewed by all authors, and data considered to be potentially relevant to the contribution of hygiene-related immune variables to major depressive disorder were extracted.
Data Synthesis: Significant data suggest that a variety of microorganisms (frequently referred to as the "old friends") were tasked by coevolutionary processes with training the human immune system to tolerate a wide array of nonthreatening but potentially proinflammatory stimuli. Lacking such immune training, vulnerable individuals in the modern world are at significantly increased risk of mounting inappropriate inflammatory attacks on harmless environmental antigens (leading to asthma), benign food contents and commensals in the gut (leading to inflammatory bowel disease), or self-antigens (leading to any of a host of autoimmune diseases). Loss of exposure to the old friends may promote MDD by increasing background levels of depressogenic cytokines and may predispose vulnerable individuals in industrialized societies to mount inappropriately aggressive inflammatory responses to psychosocial stressors, again leading to increased rates of depression.
Conclusion: Measured exposure to the old friends or their antigens may offer promise for the prevention and treatment of MDD in modern industrialized societies.
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The Epigenetics of Suicide: Explaining the Biological Effects of Early Life Environmental Adversity
Benoit Labonte & Gustavo Turecki
Archives of Suicide Research, October 2010, Pages 291-310
Abstract:
A number of recent studies have shown epigenetic alterations associated with suicidal behavior. These epigenetic mechanisms, which alter gene expression via alternative mechanisms to the coding DNA sequence, result from environmental effects acting on the genome. Studies in rodents indicate that variation in the early environment will trigger these epigenetic modifications and recent human data suggest the same may be true in humans. The expression of a number of genes, which are involved in normal brain functions and that have been shown to be under epigenetic control, seem to be dysregulated in suicide. The present review briefly describes the main epigenetic mechanisms involved in the regulation of gene expression and discusses recent findings of epigenetic alterations in suicidal behavior.
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An Evolutionary Account of Suicide Attacks: The Kamikaze Case
John Orbell & Tomonori Morikawa
Political Psychology, forthcoming
Abstract:
Explanations for suicide attacks abound. Yet the literature remains conceptually fragmented, with different authors focusing on different attitudes, incentive structures, values, psychological processes, strategic imperatives, and cultural, historical, and personal circumstances. Curiously, however, there have been few efforts to cast suicide bombing within the extensive evolutionary literature on human altruism - in which it clearly belongs. Neither have there been more than occasional efforts to mobilize the distinction between "proximate" and "ultimate" explanations, with most proposed explanations being proximate. Here we draw on content analyses from materials written by Japanese Kamikaze pilots to propose an evolvable cognitive algorithm - by hypothesis, species typical - that (1) specifies environmental circumstances under which such "heroic" behavior is likely; (2) is consistent at the proximate level with the Japanese data; and (3) that is not inconsistent with many of the diverse proximate attitudes, values, and psychological mechanisms that dominate discussions of contemporary suicide campaigns. The evolutionary perspective is not an alternative to most of the proximate explanations offered in discussions of contemporary cases but is, rather, a paradigm around which diverse proximate explanations can be organized.
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Bones in the rebel lady's boudoir: Ethnology, race and trophy-hunting in the American Civil War
Simon Harrison
Journal of Material Culture, December 2010, Pages 385-401
Abstract:
This article discusses the collection and use of enemy skulls and other bones as trophies by soldiers and their supporters in the American Civil War. This behaviour was condemned at the time as that of ‘savages'. However, the author argues that it was a local symptom of the shifts taking place after the Enlightenment in the ways in which human diversity was conceptualized. Civil War soldiers who collected and displayed their enemies' remains did so for some of the same reasons that comparative anatomists had begun to collect, display and study such objects at the time. They, too, assumed that the fundamental material evidence of human differences lay under the skin, in the bones and, above all, in the skull.
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Anders Björklund, Lena Lindahl & Matthew Lindquist
B.E. Journal of Economic Analysis & Policy, November 2010
Abstract:
Sibling correlations are broader measures of the impact of family and community influences on individual outcomes than intergenerational correlations. Estimates of such correlations in income show that more than half of the family and community influences that siblings share are uncorrelated with parental income. We employ a data set with rich family information to explore what factors in addition to traditional measures of parents' socio-economic status can explain sibling similarity in long-run income. Measures of family structure and social problems account for very little of sibling similarities beyond that already accounted for by income, education and occupation. However, when we add indicators of parental involvement in schoolwork, parenting practices and maternal attitudes, the explanatory power of our variables increases from about one-quarter (using only traditional measures of parents' socio-economic status) to nearly two-thirds.
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Charlie Reeve & Debra Basalik
Intelligence, January-February 2011, Pages 64-73
Abstract:
The current study examines the degree to which state intellectual capital, state religiosity and reproductive health form a meaningful nexus of ecological relations. Though the specific magnitude of effects vary across outcomes, results from hierarchical regression analyses were consistent with the hypothesized path model indicating that a state's intellectual capital (as indicated by average state IQ and graduation rates at various levels) has a positive overall effect on state reproductive health statistics, whereas state religiosity generally has a negative impact. Specifically, both IQ and education were positively associated with breastfeeding rates, immunization rates, and rates of mammography screening, and negatively associated with teen fertility rates and infant mortality rates. Additionally, results confirm that education rates partially mediate the influence of IQ onto religiosity, and both education and religiosity partially or fully mediate the relation between IQ and state health (depending on specific outcome measure). The current results are consistent with a growing interdisciplinary literature establishing that individual, state and national well-being is substantially related to general mental ability and its covariates.
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Abortion Incidence and Access to Services In the United States, 2008
Rachel Jones & Kathryn Kooistra
Perspectives on Sexual and Reproductive Health, forthcoming
Context: The incidence of abortion has declined nearly every year between 1990 and 2005, but this trend may be ending, or at least leveling off. Access to abortion services is a critical issue, particularly since the number of abortion providers has been falling for the last three decades.
Methods: In 2009 and 2010, all facilities known or expected to have provided abortion services in 2007 and 2008 were contacted, including hospitals, clinics and physicians' offices. Data on the number of abortions performed were collected and combined with population data to estimate national and state-level abortion rates. Abortion incidence, provision of early medication abortion, gestational limits, charges and antiabortion harassment were assessed by provider type and abortion caseload.
Results: In 2008, an estimated 1.21 million abortions were performed in the United States. The abortion rate increased 1% between 2005 and 2008, from 19.4 to 19.6 abortions per 1,000 women aged 15-44; the total number of abortion providers was virtually unchanged. Small changes in national abortion incidence and number of providers masked substantial changes in some states. Accessibility of services changed little: In both years, 35% of women of reproductive age lived in the 87% of counties that lacked a provider. Fifty-seven percent of nonhospital providers experienced antiabortion harassment in 2008; levels of harassment were particularly high in the Midwest (85%) and the South (75%).
Conclusions: The long-term decline in abortion incidence has stalled. Higher levels of harassment in some regions suggest the need to enact and enforce laws that prohibit the more intrusive forms of harassment.
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Human Capital and Interethnic Marriage Decisions
Delia Furtado
Economic Inquiry, forthcoming
Abstract:
Common explanations for the generally negative relationship between education and ethnic endogamy include (1) education makes immigrants and their children better able to adapt to native culture thereby eliminating the need for a same-ethnicity spouse and (2) education raises the likelihood of leaving ethnic enclaves, thereby decreasing the probability of meeting potential same-ethnicity spouses. This paper considers a third option, the role of assortative matching on education. If education distributions differ by ethnicity, then spouse-searchers may trade similarities in ethnicity for similarities in education when choosing spouses. U.S. Census data on second-generation immigrants provide strong support for the assortative matching mechanism.
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Benjamin Carone et al.
Cell, 23 December 2010, Pages 1084-1096
Abstract:
Epigenetic information can be inherited through the mammalian germline and represents a plausible transgenerational carrier of environmental information. To test whether transgenerational inheritance of environmental information occurs in mammals, we carried out an expression profiling screen for genes in mice that responded to paternal diet. Offspring of males fed a low-protein diet exhibited elevated hepatic expression of many genes involved in lipid and cholesterol biosynthesis and decreased levels of cholesterol esters, relative to the offspring of males fed a control diet. Epigenomic profiling of offspring livers revealed numerous modest (20%) changes in cytosine methylation depending on paternal diet, including reproducible changes in methylation over a likely enhancer for the key lipid regulator Ppara. These results, in conjunction with recent human epidemiological data, indicate that parental diet can affect cholesterol and lipid metabolism in offspring and define a model system to study environmental reprogramming of the heritable epigenome.
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Heritable victimization and the benefits of agonistic relationships
Amanda Lea, Daniel Blumstein, Tina Wey & Julien Martin
Proceedings of the National Academy of Sciences, 14 December 2010, Pages 21587-21592
Abstract:
Here, we present estimates of heritability and selection on network traits in a single population, allowing us to address the evolutionary potential of social behavior and the poorly understood link between sociality and fitness. To evolve, sociality must have some heritable basis, yet the heritability of social relationships is largely unknown. Recent advances in both social network analyses and quantitative genetics allow us to quantify attributes of social relationships and estimate their heritability in free-living populations. Our analyses addressed a variety of measures (in-degree, out-degree, attractiveness, expansiveness, embeddedness, and betweenness), and we hypothesized that traits reflecting relationships controlled by an individual (i.e., those that the individual initiated or were directly involved in) would be more heritable than those based largely on the behavior of conspecifics. Identifying patterns of heritability and selection among related traits may provide insight into which types of relationships are important in animal societies. As expected, we found that variation in indirect measures was largely explained by nongenetic variation. Yet, surprisingly, traits capturing initiated interactions do not possess significant additive genetic variation, whereas measures of received interactions are heritable. Measures describing initiated aggression and position in an agonistic network are under selection (0.3 < |S| < 0.4), although advantageous trait values are not inherited by offspring. It appears that agonistic relationships positively influence fitness and seemingly costly or harmful ties may, in fact, be beneficial. Our study highlights the importance of studying agonistic as well as affiliative relationships to understand fully the connections between sociality and fitness.
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Qin Zhu & Geoffrey Bingham
Evolution and Human Behavior, forthcoming
Abstract:
Long-distance throwing is uniquely human and enabled Homo sapiens to survive and even thrive during the ice ages. The precise motoric timing required relates throwing and speech abilities as dependent on the same uniquely human brain structures. Evidence from studies of brain evolution is consistent with this understanding of the evolution and success of H. sapiens. Recent theories of language development find readiness to develop language capabilities in perceptual biases that help generate ability to detect relevant higher order acoustic units that underlie speech. Might human throwing capabilities exhibit similar forms of readiness? Recently, human perception of optimal objects for long-distance throwing was found to exhibit a size-weight relation similar to the size-weight illusion; greater weights were picked for larger objects and were thrown the farthest. The size-weight illusion is: lift two objects of equal mass but different size, the larger is misperceived to be less heavy than the smaller. The illusion is reliable and robust. It persists when people know the masses are equal and handle objects properly. Children less than 2 years of age exhibit it. These findings suggest the illusion is intrinsic to humans. Here we show that perception of heaviness (including the illusion) and perception of optimal objects for throwing are equivalent. Thus, the illusion is functional, not a misperception: optimal objects for throwing are picked as having a particular heaviness. The best heaviness is learned while acquiring throwing skill. We suggest that the illusion is a perceptual bias that reflects readiness to acquire fully functional throwing ability. This unites human throwing and speaking abilities in development in a manner that is consistent with the evolutionary history.
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Characteristics of men willing to act as sperm donors in the context of identity-release legislation
Damien Riggs & Laura Russell
Human Reproduction, January 2011, Pages 266-272
Background: Although ongoing legislative changes are important to protect the rights of all involved in assisted reproductive technologies, it cannot be guaranteed that legislation will ensure the successful operation of reproductive health clinics, as is indicated by ongoing reports of a dearth of donor sperm in clinics in some countries.
Methods: Data were 1428 profiles taken from a website that aims to facilitate relationships between those seeking donor sperm and men willing to donate their sperm. Data were coded as three independent variables: age, relationship status and country, and four dependent variables: motivation to donate, willingness to be identified, willingness to be involved with children conceived of donations and beliefs about who should determine the level of involvement.
Results: Non-parametric testing indicated that men aged under 26 or over 46, and who were either single or in a same-sex relationship, were most likely to be willing to be identified to children (P< 0.05), and to desire involvement with children (P< 0.01). A significant proportion of men aged between 26 and 46 years of age (P< 0.001) were motivated by a desire to procreate and were unwilling to be identified, as were a significant number of men in opposite-sex relationships (P< 0.001).
Conclusions: Although limited by its reliance upon a sample constituted by men living in western countries who completed a self-report profile and who had not received counselling about their potential role as donors, this study draws attention to the potential impact of age and sexual orientation upon intentions to donate.
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Height of Female Americans in the 19th century and the Antebellum Puzzle
Scott Alan Carson
Economics & Human Biology, forthcoming
Abstract:
Using 19th century state prison records, this study contrasts the biological standard of living of comparable US African-American and white females during a period of relatively rapid economic development. White females were consistently taller than black females by about 1.5 cm (0.6 in.). Whites from Great Lakes and Plains states and black Southwestern females were the tallest. US females were tall compared to their European counterparts. The height of females began to decline in the antebellum period, possibly before that of males. The recovery of physical stature was also earlier among females than among males. This implies that the biological standard of lower-class men and women did not move in parallel during the onset of modern economic growth. It also implies that the antebellum puzzle was most likely rooted in the endogenous forces of socio-economic change rather than the exogenous changes in the disease environment.