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 very maladaptive are passed on to the next generation.
Below we will look at 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.
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 That is to say, it is about the fact that some genes are passed on to the next generation not because the individuals survive on their own, but rather because, with the help of relatives, they have an easier time reaching adulthood and reproducing, passing the genes on to the next generation. generation.
According to classical Darwinian theory, an individual that has more favorable characteristics will have an easier time reaching adulthood and being able to reproduce, passing its genes to the next generation. If he presents unfavorable traits, it is most likely that he will either fail to be reproductively attractive and will not be able to mate or, directly, that he will not reach adulthood alive, causing his genes to die with him. All this is the basic foundation of the idea of natural selection.
This theory is already part of our popular culture but, although it is widely accepted, it fails to explain why maladaptive genes continue to persist. There are many negative traits that have been passed down from generation to generation. Sooner or later those genes would have disappeared, since its individuals would be very unlikely to reproduce. The only way these individuals would have to reproduce was for their peers to be altruistic and help them survive.
However, this still raised more questions than answers. Why were animals sacrificed for others? It did not make sense. On many occasions, the animal, by performing 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 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 survive not out of pure empathy or desire to help, but as another evolutionary mechanism.
That one relative sacrifices himself for another should not be seen as an adaptively counterproductive act, quite the opposite. Sacrificing yourself for a relative, with whom you share a lot of genetic material, is a way to ensure that those same genes are passed on to the next generation. Obviously, it is preferable that the individual does not sacrifice himself and that he himself 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 worthwhile to behave altruistically for the common good
Hamilton’s rule
To understand the idea of kin selection a little more deeply, it is necessary to talk a little about Hamilton’s rule, a simple equation that receives its name from the same William D. Hamilton that we 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 in frequency in a given population, that is, a greater or lesser percentage of individuals with those genes would be expected, 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 randomly chosen gene at the same locus (place on a chromosome) in both individuals is identical by descent.
B = is the additional reproductive benefit received by the recipient of the altruistic act. C = is the reproductive cost suffered by the donor.
Kin selection cases in nature
All social species seem to carry out 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 family members such as brothers, biological nephews and cousins long before second cousins or more or less distant relatives who, despite having the same surnames, are so strange and different. genetically like any person on the street.
This makes sense if you think in percentages of shared genetic material With a brother 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 oneself for a brother would be the closest thing to being able to reproduce for ourselves if that were not possible.
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 kin selection.
1. Bees
Bees are animals with haplodiploidy, that is, some individuals, in this case males, have a single 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 capable of giving their lives for the hive. In fact, The relationship coefficient 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 her being the main reproducer, they share a lot of genetic material with her. By saving the queen, the workers manage to pass their genes 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 fleeing, decide to attract attention They start making noises to save their fellow humans and make the predator go to where they are.
It is clear that, if the predator finds where the “savior” squirrels are, it will attack them 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 one life, the more likely it is that the same genes will be passed on to the next generation.
