Genetic similarity, human altruism, and group selection

Genetic similarity, human altruism, and group selection

J. Philippe Rushton (1989)

Abstract: A new theory of attraction and liking based on kin selection suggests that people detect genetic similarity in others in order to give preferential treatment to those who are most similar to themselves. There are many sources of empirical and theoretical support for this view, including (1) the inclusive fitness theory of altruism, (2) kin recognition studies of animals raised apart, (3) assortative mating studies, (4) favoritism in families, (5) selective similarity among friends, and (6) ethnocentrism. Specific tests of the theory show that (1) sexually interacting couples who produce a child are genetically more similar to each other in blood antigens than they are either to sexually interacting couples who fail to produce a child or to randomly paired couples from the same sample; (2) similarity between marriage partners is most marked in the more genetically influenced of sets of anthropometric, cognitive, and personality characteristics; (3) after the death of a child, parental grief intensity is correlated with the child’s similarity to the parent; (4) long-term male friendship pairs are more similar to each other in blood antigens than they are to random dyads from the same sample; and (5) similarity among best friends is most marked in the more genetically influenced of sets of attitudinal, personality, and anthropometric characteristics. The mechanisms underlying these findings may constitute a biological substrate of ethnocentrism, enabling group selection to occur.

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Genetic Influence on Risk of Divorce

Genetic Influence on Risk of Divorce

Matt McGue and David T. Lykken (1992)

Department of Psychology, University of Minnesota

Abstract – Although it has long been recognized that there is increased risk of divorce among the children of divorced parents, the extent to which genetic and environmental factors contribute to this familial resemblance has been a matter of speculation only. In order to resolve the separate influence of genetic and environmental factors on risk of divorce, divorce status of 1,516 same-sex twin pairs (722 monozygotic. MZ, and 794 dizygotic, DZ), their parents, and their spouses’ parents was determined. Concordance for divorce was significantly higher in MZ than DZ twins; this was true overall, in both the male and female samples, for both younger and older twin pairs, and both when the twins’ parents had been divorced and when they had not been divorced. The robustness and magnitude of the MZ-DZ difference in divorce concordance indicates a strong influence of genetic factors in the etiology of divorce. Moreover, family background of both spouses contributed independently to couples’ divorce risk, suggesting that, in many cases, divorce may be largely the result of characteristics the two spouses bring to the union rather than to interaction effects. These results also suggest that the adjustment difficulties seen with some children of divorced parents may be dice to an interaction between genetic and environmental factors rather than environmental influences alone, as is assumed in many theories of divorce’s effects.

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Do People Make Environments or Do Environments Make People?

Do People Make Environments or Do Environments Make People?


ABSTRACT: This article discusses the influence of people’s genetic make-up on their mental states of happiness and depression. Contrary to the conventional wisdom, great fortune does not guarantee happiness; neither does great misfortune assure depression. Emotional states are surprisingly immune to “objective” social circumstances. A biological basis for this relative immunity is that people possess biological set points for these emotional states, rendering the effects of most life events transitory. Genotypes also have indirect effects. People react differently to psychological stressors depending on their genotypes. A susceptible person may succumb to depression, whereas a resilient person may remain unaffected. People also expose themselves to different social environments. Exposure to controllable life events is partly a result of genetic predispositions. Consilience requires that this biological individuality be considered in any understanding of human behavior, including the pursuit of happiness.

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Genetic influences on ‘environmental’ factors

Genetic influences on ‘environmental’ factors

A. A. E. Vinkhuyzen, S. van der Sluis, E. J. C. de Geus, D. I. Boomsma and D. Posthuma (2009)

Childhood environment, social environment and behavior, leisure time activities and life events have been hypothesized to contribute to individual differences in cognitive abilities and physical and emotional well-being. These factors are often labeled ‘environmental’, suggesting they shape but not reflect individual differences in behavior. The aim of this study is to test the hypothesis that these factors are not randomly distributed across the population but reflect heritable individual differences. Self-report data on Childhood Environment, Social Environment and Behavior, Leisure Time Activities and Life Events were obtained from 560 adult twins and siblings (mean age 47.11 years). Results clearly show considerable genetic influences on these factors with mean broad heritability of 0.49 (0.00–0.87). This suggests that what we think of as measures of ‘environment’ are better described as external factors that might be partly under genetic control. Understanding causes of individual differences in external factors may aid in clarifying the intricate nature between genetic and environmental influences on complex traits.

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The Savanna Principle

The Savanna Principle

Satoshi Kanazawa
Manage. Decis. Econ. 25: 41–54 (2004)


For instance, one of the entities that we know for sure did not exist in the EEA is television. The fundamental principles of EP would therefore imply that humans have difficulty recognizing and dealing with TV. This indeed appears to be the case. People who watch certain types of TV shows are more satisfied with their friendships, just like they are if they have more friends or spend more time socializing with them in real life. It appears that the human brain has difficulty distinguishing between real friends and imaginary ones they see on TV, because it did not exist in the EEA (Kanazawa, 2002). It is this fundamental observation, that our brain and its psychological mechanisms are strongly biased to view and respond to the environment as if it were still the EEA, which leads to the Savanna Principle.

It is true, as critics of EP often point out, that the EEA, tens of thousands of years past, is not directly observable. We can make inferences about it, based both on archeological records and ethnography of contemporary hunter-gatherer societies, but it is unlikely that we will ever know all the details of the EEA. It is therefore impossible for us to draw all the implications of the above observation for our current social behavior. However, there are certain things about our ancestral life in the EEA that we know reasonably well. We know that our ancestors lived in small bands not exceeding 200 individuals; they did not live in a metropolis where everybody can be anonymous. We know that all communications between people in the EEA were direct and face-to-face; they did not have telephones, computers or even writing that allowed them to communicate without facing each other. It is my suggestion in this paper that these few facts that we know about the EEA are sufficient to use the Savanna Principle to figure out which hypotheses about human behavior are likely to fail and why.

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De Gustibus Est Disputandum

De Gustibus Est Disputandum

SATOSHI KANAZAWA, Indiana University of Pennsylvania, 2001.

Principles of Evolutionary Psychology

Our preference for sweets and fats is an example of an evolved psychological mechanism (Barash 1982:144-47). Throughout most of human evolutionary history, procurement of sufficient calories to sustain our bodies physically was a particularly severe problem of adaptation (survival); malnutrition was a common problem. In this environment, those who had a “taste” for sweets and fats (which have higher calories) were better off physically than those who did not have the same taste. Those who had this taste therefore lived longer, led healthier lives and produced higher-quality offspring than those who didn’t. They in turn passed on their taste to their offspring, over many thousands of generations, until most of us living today have a strong preference for sweets and fats. (See Buss 1995:5-9 for other examples of evolved psychological mechanisms.)

Note that we do not consciously choose or decide to like sweets and fats. We just like them but otherwise don’t know why; sweet and fatty foods just taste good to us. […]

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