Kin win to become item 15,000 in the St Andrews Research Repository
To mark the 15,000th item deposited in the St Andrews Research Repository the Open Access Support team is pleased to publish a guest post by its co-author, Andy Gardner:
Dyble, M, Gardner, A, Vinicius, L & Migliano, A 2018, ‘Inclusive fitness for in-laws’ Biology Letters, vol. 14, no. 10. DOI: 10.1098/rsbl.2018.0515
Cooperation abounds in nature and in human society, and this has long been a puzzle for evolutionary biologists. At first glance, the traditional Darwinian dictum of the “survival of the fittest” appears to imply that selfishness will reign supreme. But altruism can be favoured by natural selection, if it occurs between closely-related kin. According to the theory of “kin selection”, although a gene encoding altruistic behaviour leads to its carrier suffering a cost, it is also providing a benefit to other individuals who carry copies of the very same gene, and this increases its overall transmission to future generations.
However, human notions of kinship extend beyond the strictly genetical, to include “affines” who are related through marriage rather than by blood. And anthropologists have long noted that we often behave altruistically towards our in-laws, even if we don’t share any genes in common.
In this paper, we asked if the theory of kin selection can be reframed to explain such behaviour, and we found that it can, because although the altruist might not share genes with her in-laws, she might share genes with their children. For example, a woman who behaves altruistically towards her daughter-in-law will tend to have more grandchildren, who will carry copies of her own genes that they have inherited from their father — her son. We mathematically quantified the degree of shared reproductive interest between different ranks of in-laws, to see just how willing an individual should be to perform such acts of altruism.
The evolutionary theorist W. D. Hamilton once summarised the theory of kin selection by noting that “an animal acting on this principle would sacrifice its life if it could thereby save more than two brothers, but not for less”. Our analysis shows that, depending on marriage customs, a person might be willing to do the same for their brothers’ wives.