Born, grow, reproduce, collaborate and die. The killer whale is one of the 3 known species of animals, in addition to humans, that reaches menopause and, like us, continues to live many more years after ceasing to be fertile. When they stop reproducing, orcas spend their “old age” years helping their adult calves feed and care for the new killer whales . But it seems that this role, adopted by the older killer whales, is not simple altruism, but a question of survival: they lose in the evolutionary race against younger females.
This is the conclusion reached by a British study published by the journal Current Biology in May 2017, which explains why killer whales reach menopause and therefore stop reproducing. According to research, older killer whale calves are much less likely to thrive than younger killer whale calves. Specifically, 1.7 times less.
That orcas adopt a collaborative role with great benefits for the family group was already known by the scientific community thanks to previous studies. But that was not enough to explain why females stop reproducing. “Many older females of other species take a leadership role and still continue to reproduce,” explains Darren Croft, co-author of the study, from the University of Exeter, UK. “Our study provides a mechanism that explains why older killer whales stop having offspring, and that is that they lose the competition against their daughters .”
A finding that can even be extrapolated to human evolution. The reproductive conflict experienced by different generations of killer whales could also have occurred in the origins of Homo sapiens . Evolution would favor young females who invest more efforts in reproduction , while older females, closer to family members of the same age, would dedicate their efforts to collaborative family tasks . A hypothesis that now seems to hold true in the case of killer whales, which can reach 90 years of age.
Now, the objective of the researchers is to verify the behavior patterns adopted by older and younger females at the time of breeding. A team from the University of York intends to introduce drones to obtain a “bird’s eye view” to observe how the behavior of young and old females intervenes in the survival of the young. An empirical study that would serve to corroborate the reproductive conflict hypothesis.
