Thomas V. Pollet

Natural selection on male wealth in humans.

Although genomic studies suggest that natural selection in humans is ongoing, the strength of selection acting on particular characteristics in human populations has rarely been measured. Positive selection on male wealth appears to be a recurrent feature of human agrarian and pastoralist societies, and there is some evidence of it in industrial populations, too. Here we investigate the strength of selection on male wealth, first in contemporary Britain using data from the National Child Development Study and then across seven other varied human societies. The British data show positive selection on male income driven by increased childlessness among low‐income men but a negative association between personal income and reproductive success for women. Across cultures, selection gradients for male wealth are weakest in industrial countries and strongest in subsistence societies with extensive polygyny. Even the weakest selection gradients observed for male wealth in humans are as strong as or stronger than selection gradients reported from field studies of other species. Thus, selection on male wealth in contemporary humans appears to be ubiquitous and substantial in strength.

Driving a hard bargain: sex ratio and male marriage success in a historical US population

Evolutionary psychologists have documented a widespread female preference for men of high status and resources, and evidence from several populations suggests that this preference has real effects on marriage success. Here, we show that in the US population of 1910, socioeconomic status (SES) had a positive effect on mens chances of marrying. We also test a further prediction from the biological markets theory, namely that where the local sex ratio produces an oversupply of men, women will be able to drive a harder bargain. As the sex ratio of the states increases, the effect of SES on marriage success becomes stronger, indicating increased competition between men and an increased ability to choose on the part of women.

Taller women do better in a stressed environment: height and reproductive success in rural Guatemalan women.

Previous research on the relationship between height and reproductive success in women has produced mixed results. One possible explanation for these is mediation by ecological factors, such as environmental stress. Here we investigate female height and reproductive success under conditions of environmental stress (poverty) using a large scale dataset from Guatemala (n = 2,571). Controlling for educational attainment, age and ethnicity, we examined relationships between height and childlessness, occurrence of a stillbirth, fertility and child survival. There was no significant relationship between height and never haven given birth. Extremely short women had a significantly raised likelihood of experiencing stillbirth. There were curvilinear relationships between height and age at first birth, fertility, and survival rates for children. Overall, though, the penalties for short stature, particularly in terms of child survival, were far greater than those associated with extreme tallness, and so female height is positively associated with overall fitness in this population. Am. J. Hum. Biol., 2008.

CONTACT FREQUENCIES BETWEEN GRANDPARENTS AND GRANDCHILDREN IN A MODERN SOCIETY: ESTIMATES OF THE IMPACT OF PATERNITY UNCERTAINTY

Evolutionary theory suggests that maternal grandparents will invest more in their grandchildren than paternal grandparents, due to the difference between the certainty of maternity and the uncertainty of paternity. Tests of this prediction have tended to use retrospective ratings by grandchildren rather than self-reported behaviour by grandparents. Using a large-scale dataset from the Netherlands, we show significant differences between maternal and paternal grandparents in terms of frequencies of contact with their grandchildren, while controlling for a wide range of other variables. Our results show biases consistent with the paternity uncertainty hypothesis.

Maternal Grandmothers Do Go the Extra Mile: Factoring Distance and Lineage into Differential Contact with Grandchildren

Several studies conducted from an evolutionary perspective have documented differential investment in grandchildren by lineage. The majority of these studies have used retrospective ratings by grandchildren, but only a fraction of these studies have examined actual grandparental behavior. Here we focus on the interaction between distance and lineage on face-to-face contact with a (random) grandchild in a large scale sample. Our main prediction is that maternal grandparents are significantly more willing to travel in order to see their grandchild. While controlling for initiative of contact, urbanization, sex and age of the grandchild, educational attainment, marital status and age we found a significant interaction between distance and grandparent type on frequency of contact with a grandchild. Maternal grandmothers were significantly more inclined than paternal grandfathers and grandmothers to maintain frequent face-to-face contact, as distance between grandparent and grandchild increased. The results are discussed with reference to evolutionary theories of grandparental investment.

CHILDLESSNESS PREDICTS HELPING OF NIECES AND NEPHEWS IN UNITED STATES, 1910

The helpers at the nest hypothesis suggests that individuals who are not currently reproducing often help kin by caretaking and thereby increase their inclusive fitness. Using a large scale historical dataset (Integrated Public Use Microdata Series sample of 1910; n=13,935), the hypothesis is tested that childless couples are more likely to fulfil such a role by taking care of a niece or nephew, but not a parent, than couples with children. Childless couples were significantly more likely to take care of a niece or nephew than couples with children. In contrast, couples with children and childless couples did not differ in caretaking of parents. Childless couples were also more likely to have more and younger nieces/nephews in their home than couples with children.

Dead or alive? Knowledge about a sibling’s death varies by genetic relatedness in a modern society

Using a large sample of non-institutionalized individuals from the Netherlands (n = 7610), we examined the influence of relatedness on an individuals knowledge about whether their sibling is alive or not. Respondents were generally less likely to know whether their sibling was alive if they were not fully related. The effects were stronger for differences between paternal half-siblings and full siblings than for differences between maternal half-siblings and full siblings.