Animal 'infanticide': why do some species kill their young?

Science | biology

The fight between two brown bears in the Palentina Mountain has generated surprise due to the brutality of the event, but it is nothing new

Elena Martin Lopez

In terms of human life, few behaviors are as socially condemned as the act of killing a child. In the animal kingdom, on the other hand, infanticide is a fairly common behavior. Hence, although the video of the fight between two brown bears that rush down a cliff in the Palentina Mountain, after the female tries to protect her cub from the male's attack, is so striking, this behavior does not surprise biologists.

The explanation lies in the mating and elimination of the competition. "By killing the offspring that are not his, a male seeks to eliminate the competition of the previous offspring and for the female to be fertile again to engender his own offspring with her," explains José María Santiago Sáez, a biologist at the Official College of Biologists of the Community of Madrid. It seems that this was the reason that led to the tragic scene that has gone viral.

That does not mean that infanticide is not harmful to females, who see all the effort they have put into fathering their young being wasted. That is why they have developed defense strategies. “One of them is to settle in steep and remote places where the probability of encountering another bear is low, such as the boulder that appears in the video. Another is to fight, as also happens in the recording. And a third is polyandry; that is to say, the females are very promiscuous and mate with several males at the same time so that the latter, not knowing which ones are their offspring and which ones are not, refrain from killing them", declares Fernando Ballesteros, project coordinator of the Fundación Oso Brown.

Other infanticidal species

Beyond bears, infanticide is also common among many other species, such as some felines, primates or rodents. For example, “when a male lion takes control of a pride by dethroning the previous alpha male, it is customary for him to kill offspring that are not his own so that the females can conceive new cubs of which he is the father” , explains Santiago Saez.

It seems like a boycott of the species itself, but evolutionarily it is a system that has worked well, that is why it is maintained. "If infanticide reduced the possibility of population growth to serious limits, it would disappear from the evolutionary process, but the truth is that the small populations of brown bear that we have continue to grow every year despite suffering annual infanticides," says Ballesteros.

It is a survival mechanism. "It is assumed that the individuals that do this are the best competitors, because they are the ones that come to dominate the group, and therefore have the best skills to pass on to the offspring and ensure that the species survives," adds Santiago Saez.

Some studies maintain that infanticide occurs, above all, in species whose females can procreate throughout the year, but not in those with a seasonal reproductive cycle. In addition, it seems linked to those species in which a few males mate with multiple females, it may be due to behavioral abnormalities of a pathological nature, and it is related, to a greater extent, to animals whose offspring are very numerous or that require less care of the mother. "The less effort dedicated to caring for the children, the easier it is to prey on the young themselves," says Santiago Sáez.

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