Kinship selection: what it is and how it is expressed.

A concept that explains altruistic behavior linked to inbreeding.

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

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

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

• Related article, "What is Ethology and what is its object of study?"

What is kin selection?

Kinship selection, also called familial selection, refers to changes in gene frequencies across generations that are due, for the most part, to interactions between related individuals. changes in gene frequencies across generations that are due, for the most part, to interactions between related individuals.. In other words, genes are passed on to the next generation not because individuals survive on their own, but because, with the help of relatives, they have an easier time reaching adulthood and reproducing, passing the genes on to the next generation.

According to classical Darwinian theory, an individual with more favorable characteristics will have an easier time reaching adulthood and being able to reproduce, passing its genes to the next generation. In the case of unfavorable traits, it is most likely that it will either fail to be reproductively conspicuous and will not be able to mate or, directly, that it will not reach adulthood alive, causing its genes to die with it. All this is the basic foundation of the idea of natural selection.

This theory is now part of our popular culture but, although it is widely accepted, it fails to explain why maladaptive genes continue to persist. More than a few negative traits have been passed on from generation to generation. Sooner or later these genes would have disappearedSooner or later these genes would have disappeared, since it would be very difficult for their individuals to reproduce. The only way for these individuals to reproduce was for their conspecifics to be altruistic and help them to survive.

However, this still raised more questions than answers. Why did animals sacrifice themselves for others? It did not make sense. On many occasions, the animal, when performing an altruistic behavior that benefited a less fit animal, not only lost some advantage, but also ran the risk of losing its life. However, someone had the brilliant idea of asking, 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 sociobiology, who proposed an explanation of animal altruism based on the idea of kin selection. According to him, an animal would help others to survive not out of pure empathy or desire to help, but as a further evolutionary mechanism.

That one kin sacrifices itself for another should not be seen as an adaptively counterproductive act, quite the contrary. Sacrificing oneself for a relative, with whom one shares a lot of genetic material, is a way of guaranteeing that the same genes will be passed on to the next generation. Obviously, it is preferable that the individual does not sacrifice himself and it is he himself who reproduces 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 profitable to behave as a group, in terms of group cost-benefit it is more profitable to behave altruistically for the common good..

Hamilton's rule

To understand a little more deeply the idea of kin selection, it is necessary to talk a little about Hamilton's rule, a simple equation named after the same William D. Hamilton mentioned above. This geneticist published in 1964 the first quantitative study of kinship selection to explain evolution in apparently altruistic acts.

Formally, genes would increase their frequency in a given population, i.e., one would 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 relatedness between the recipient and the donor, defined as the probability that a randomly chosen gene at the same locus (place on a chromosome) in both individuals will be identical by offspring.

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

Cases of kin selection in nature

All social species appear to engage in prosocial and altruistic behavior to a greater or lesser extent.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 siblings, Biological nephews and cousins much before 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 has its logic if you think in terms of percentages of shared genetic material. With a sibling of the same parents we share about 50% of the genetic material, while with a biological nephew the percentage drops to 25% and with a cousin to 12.5%. Sacrificing ourselves for a sibling would be the closest thing to being able to reproduce ourselves in case we were not able to do so.

We will now look at two specific cases of animal species in which altruistic behaviors can be observed, where the percentages of shared genetic material are high and which fit with the theory of kin selection.

1. Bees

Bees are haplodiploid animals, i.e., some individuals, in this case males, have a unique set of each chromosome, while females, which are workers and queens, have a pair of chromosomes of each type.

Females, regardless of whether they are workers or queens, have a lot of genetic material in common, and that is why workers are able to give 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, worker bees are capable of sacrificing themselves for the queen because, in addition to being the queen's main reproductive agent, 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. Squirrels

The case of squirrels is particularly interesting. When a predator appears and approaches one of these rodents, the other squirrels in hiding, far from fleeing, run away, the other squirrels that are hiding, far from fleeing, decide to attract the attention of the predators.. They start making noises to save their fellow squirrel and make the predator come to them.

It is clear that, in case the predator finds where the "saving" squirrels are, it will 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 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 the life of one, the more likely it is that the same genes will be passed on to the next generation.

Referencias bibliográficas:

• Hamilton, W. D. (1964). The genetical evolution of social behaviour. I. Journal of Theoretical Biology 7 (1): 1 - 16.
• Hamilton, W. D. (1964): The genetical 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.