Kin selection: what it is and how it is expressed

Geneticist and biologist John Burdon Sanderson Haldane once said, "I would give my life for two brothers or eight cousins." And it is quite true that we are more capable of sacrificing ourselves for our family.

This phenomenon is closely related to kin selection., an evolutionary process that would explain many situations in which, contrary to what Darwinian theory would say, it would explain how genes that are highly maladaptive are passed on to the next generation.

Next we will see this concept in more depth, and how it occurs in some social species and to what degree altruism and prosocial behaviors have a lot to do with it.

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What is kin selection?

Kin selection, also called kin selection, refers to changes in gene frequencies across generations that are due, in large part, to interactions between related individuals. In other words, it is about the fact that some genes are passed on to the next generation not because individuals survive on their own, but rather that, with the help of relatives, they have more facilities to reach adulthood and reproduce, passing the genes to the next generation.

According to classical Darwinian theory, an individual with more favorable characteristics will have more facilities to reach adulthood and be able to reproduce, passing his genes to the next generation. In case of presenting unfavorable traits, it is most likely that either it fails to be striking reproductively and cannot mate or, directly, that does not reach adulthood alive, causing their genes die with it. All this is the basic foundation of the idea of ​​natural selection.

This theory is already part of our popular culture but, despite being widely accepted, it fails to explain why maladaptive genes continue to persist. There are many negative traits that have passed from generation to generation. Sooner or later those genes would have disappeared., since its individuals would hardly reproduce. The only way these individuals would have to reproduce was for their peers to be altruistic and help them survive.

However, this continued to raise more unknowns than answers. Why were animals sacrificed for others? It did not make sense. On many occasions, the animal, by carrying out an altruistic behavior that benefited a less fit one, not only lost some advantage, but also ran the risk of losing its life. However, someone had the brilliant idea to wonder what if they are related? What if altruistic behaviors depend on the degree of consanguinity? The concept of kin selection was born.

It was William Donald Hamilton, an evolutionary biologist who is considered the precursor of the sociobiology, who proposed an explanation of animal altruism based on the idea of ​​selection of kinship. According to him, an animal would help others to survive not out of pure empathy or a desire to help, but as one more evolutionary mechanism.

That a relative sacrifices himself for another should not be seen as an adaptively counterproductive act, rather the opposite. Sacrificing for a relative, with whom you share a lot of genetic material, is one way to ensure that those same genes are passed on to the next generation. Obviously, the preferable thing is that the individual does not sacrifice himself and reproduces himself and passes on his genes, but in the event that the population to which he belongs is in serious danger, in terms of group cost-benefit, it is more appropriate to behave altruistically for the common good.

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Hamilton's rule

To understand the idea of ​​kin selection a bit more thoroughly, it is necessary to talk a little about Hamilton's rule, a simple equation that receives its name from William D. Hamilton that we have mentioned above. This geneticist published in 1964 the first quantitative study of kin selection to explain evolution in apparently altruistic acts.

Formally, genes would increase their frequency in a certain population, that is, it would be possible to expect a higher or lower percentage of individuals with those genes, taking into account the following formula:

R x B > C

R = is the genetic relationship between the recipient and the donor, defined as the probability that a gene chosen randomly at the same locus (place on a chromosome) in both individuals is identical by offspring.

B = is the additional reproductive benefit received by the recipient of the altruistic act. C = is the reproductive cost suffered by the donor.

Cases of kin selection in nature

All social species appear to engage in prosocial and altruistic behaviors., to a greater or lesser extent. For example, in the human case and paraphrasing what Haldane said, we would sacrifice a lot for relatives such as brothers, biological nephews and cousins ​​much earlier. that second cousins ​​or more or less distant relatives who, despite having the same surnames, are as strange and genetically different as any person in the street.

This is logical if one thinks in percentages of shared genetic material. With a brother of the same parents we share close to 50% of the genetic material, while with a biological nephew the percentage drops to 25% and with a cousin to 12.5%. Sacrificing for a brother would be the closest thing to being able to reproduce by ourselves in case it was not achieved.

Next we are going to see two specific cases of animal species in which altruistic behaviors can be observed, where the percentages of shared genetic material are high and that fit with the theory of the selection of relationship.

1. The bees

Bees are animals with haplodiploidy, that is, some individuals, in this case the males, have a game unique from each chromosome, while females, which are workers and queens, have a pair of chromosomes from each guy.

The females, regardless of whether they are workers or queens, have a lot of genetic material in common, and that is why the workers are capable of giving their lives for the hive. In fact, the coefficient of relatedness between worker bees and the queen bee is ¾.

When there is a threat in the hive, the workers are capable of sacrificing themselves for the queen since, in addition to being the main reproductive of the queen, they share a lot of genetic material with her. By saving the queen, the workers get their genes passed on to the next generation.

2. The squirrels

The case of squirrels is especially interesting. When a predator appears that approaches one of these rodents, the other squirrels that are hidden, far from running away, decide to attract attention. They begin to make little noises in order to save their congener and make the predator go to where they are.

It is clear that, in case the predator finds where the "rescuing" squirrels are, it will to attack or even eat them, but the squirrel that was going to be the victim will end up surviving.

They are more likely to make these little noises if the victim is closely related to them, or if there are several squirrels that could lose their lives. The more squirrels saved at the cost of one life, the more chance there is that the same genes will be passed on to the next generation.

Bibliographic references:

• Hamilton, W. d. (1964). The genetic evolution of social behaviour. YO. Journal of Theoretical Biology 7(1): 1-16.
• Hamilton, W. d. (1964): The genetic evolution of social behaviour. II. Journal of Theoretical Biology 7(1): 17-52.
• Hamilton, W. d. (1975): Innate social aptitudes of man: an approach from evolutionary genetics. In Robin Fox (ed.) Biosocial Anthropology Malaby Press, London pp.: 133-53
• Robert L Trivers (1971): The Evolution of Reciprocal Altruism The Quarterly Review of Biology 46(1): 35-57.