Bizarre study suggests men care more about their sisters' children than their own

Are men hard-wired to put the needs of their nieces and nephews over the needs of their own children? A University of Utah anthropologist conducted a mathematical analysis that could explain why some men go out of the way to care for the offspring of a sister.

Children sired from a number of partners

A husband shares a genetic legacy with his sister, as they share a common mother. In a society where infidelity is commonplace, a husband knows that all of his sister's offspring carry his genetic code. But he has no guarantee that his wife's children will. After all, she could be bearing another man's children without his knowledge.


The author of the study, University of Utah Professor of Anthropology Alan R. Rogers, explains the male's conundrum:

Imagine a mutation that encourages its bearers, if they are men, to be helpful and invest resources in the children of their sisters. If that man lives in a society where most of his wife's children were fathered by other men, then this gene may not be in many of his wife's children. A man really doesn't know if any of his wife's kids were fathered by him, but he knows he and his sister have the same mom. So this gene may, in fact, be in more of his sisters' children.

Under these conditions, the investment of a man's resources, whether it be food, shelter, time, or education, on his nieces and nephews increases the likelihood that his genetic information is passed on to coming generations. Resources spent on his children could be "wasted" from a genetic perspective.

Genetic Certainty beats Genetic Possibility

As a decrease in the confidence in paternity drops, the father may allocate resources to nieces and nephews, individuals with whom he shares a definitive genetic connection. Rogers' analysis of situations where additional care is given to nieces and nephews stems from a 1970s study that suggests an increase will only occur when the father is genetically related to a sparse 1 in 4 of his wife's children. In this study, Rogers relaxed previous assumptions to provide a more realistic scenario.

By factoring in variables including an unequal distribution of sexual encounters with extramarital partners, the resulting mathematical analysis suggests that a male would still provide additional care to his nieces and nephews if as many as 1 in 2 of his wife's offspring carried his genes.

Rogers is careful to point out that males are less likely to care for the offspring of brothers. Brothers are in the same position under these conditions of sexual reproduction with multiple partners — it is just as likely a number of his children are not genetic relatives.

You can read the entire study, Genetic relatedness to sisters' children has been underestimated, over at Proceedings of the Royal Society B.

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