Home Sciences Altruism is a product of natural selection

Altruism is a product of natural selection


Animals that help others care for their young, whether or not they are relatives, do so as a result of natural selection: they generate an evolutionary advantage for the entire group, favoring the chances of survival and the expansion of the entire herd.

Altruistic behavior is often seen as a uniquely human characteristic. Altruism is defined as doing something that benefits another person, at the expense of oneself.

In 2010 it was discovered that altruism in people could have a genetic origin. And in 2018 it was established that a social switch determines whether or not we are altruistic.

We also know that altruistic people have a larger volume of gray matter in the brain and that altruistic behavior improves physiological balance. It even has analgesic effects.

Also in the animal kingdom

Science has also discovered numerous examples of altruistic behavior in the animal kingdom. The most surprising occur in the raising of the next generation.

Animal societies that exhibit cooperative breeding include cichlids (a family of fish) in Lake Tanganyika, some mammals, many species of birds, and numerous insects.

In a new study, researchers at the University of Bern (Switzerland) have shown that animals that “selflessly” help others care for their young generate a evolutionary advantage for the whole group thanks to natural selection.

In these societies, usually a single dominant breeding pair produces young and the other members of the group help raise them. These members of the group, therefore, act altruistically by caring for offspring that are not theirs.

evolutionary perspective

This type of caretaking makes sense from an evolutionary perspective when the young are siblings of the caregivers: the caregivers successfully pass on the genes that stimulate caregiving through their siblings, with whom they share these genes.

However, from an evolutionary perspective it doesn’t seem to make sense to care for unrelated youngsters. So why do unrelated group members often help raise “foreign” young?

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The new study, published in the journal Science Advances, led by the Spanish Irene Garcia Ruiz and by the teacher Michael Taborskyboth from the Institute for Ecology and Evolution at the University of Bern, in collaboration with Andres Quinonesfrom the Universidad de Los Andes in Bogotá, Colombia, reveals how this altruistic care of the young is due to natural selection, the basis of all evolutionary change.

genetic fitness

Natural selection favors traits that improve the genetic fitness of carriers. Thanks to natural selection, individuals inherit better chances of survival and often benefit from greater reproductive success throughout their lives.

If belonging to a social group produces an essential survival advantage, cooperative breeding can be explained by the evolution. This is shown in our study, carried out using computer simulations”, explains García Ruiz in a statement.

Using mathematical models, the researchers were able to simulate group members’ altruistic decisions that affected their genetic fitness, so they could compare their resulting success rates.

They observed that when there is a survival advantage In group life, there are two ways in which natural selection causes subordinate members of the group to help care for the young of the dominant breeders.

Individual and kinship selection

One possibility occurs when youngsters are closely related, for example, when they are siblings of caregivers.

In this situation, nurturing increases the probability that genes shared between helpers and help recipients will spread to the next generation (a mechanism calledkin selection”). The evolutionary advantage is clear in this case.

The second possibility involves what is known assingle selection”, which is not constrained by kinship levels and is based on the following evidence: when altruistic brood care results in more young animals surviving, the social group expands.

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In turn, this increases the keepers’ chances of survival, because it reduces their own risk of falling victim to a predator. Therefore, the probability that they can reproduce successfully later on increases. Both selection mechanisms (kinship and individual) positively interact with each other.

Favorable conditions

“A key finding of our study is that the environmental context determines which of these two selection mechanisms comes into play, that is, which is more significant for the evolution of cooperative breeding,” explains Irene García Ruiz.

If environmental conditions are favorable (few predators), then kin selection is the most important selection mechanism for cooperative care.

But if environmental conditions are less favorable (more predators), then increasing the chances of survival of individuals, by increasing the number of group members, is the most important selection mechanism causing care of offspring by relatives. who are not their parents.

environmental context

“Whether an animal is better off staying in its territory and raising the offspring of others in the group, or rather moving elsewhere to attempt independent reproduction, varies with the age of the individual,” says Michael Taborsky.

The particularly notable finding of this study is that the relative importance of kin selection and individual selection varies by environmental context.

Also, both the age of the animals and the ecological conditions have a significant influence on the selection of philopatry (remaining in the same territory or returning to it to reproduce or nest), and altruism.


The evolution of cooperative breeding by direct and indirect fitness effects. Irene García-Ruiz et al. Science Advances, 27 May 2022; Vol 8, Issue 21. DOI: 10.1126/sciadv.abl7853

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