In humans, the role of maternal investment is already key (especially during the school period). A study has just shown how much more important it is in killer whales – for mothers, the mental load lasts a lifetime.
The science post of the weekend with Hervé Poirier, editor-in-chief of the scientific magazine Epsiloon today looks at maternal investment, already key in humans, and very important in killer whales.
franceinfo: What is called the grandmother effect would be, in killer whales, even heavier than what was supposed. That’s to say ?
Herve Poirier: During this school holiday period, some mothers and grandmothers are put to the test. I don’t know if that will relieve them, but it’s worse with orcas! Thanks to 40 years of careful monitoring of a population living in the North Pacific, biologists have been able to measure for the first time the sacrifice that maternal investment represents.
The figure is impressive: the care taken by mothers in caring for their sons reduces their reproductive success by about 50%. I say their son, because this phenomenon is only valid when they have a male: having a daughter does not influence their reproductive success in any way – orca society is very gendered. And the most impressive thing is that this cost does not diminish, as the sons age and become adults. For orca mothers, it lasts a lifetime!
Is it like some kind of mental burden that weighs on mothers?
Yes. We knew that the role of the orc grandmothers is a key factor for the cohesion of the clan, or the transmission of hunting techniques. And it is on this same population of orcas in the North Pacific that the famous “grandmother” effect was measured a few years ago: the survival rate of an orca, male or female, increases considerably. , if he has a grandmother around him.
An even more marked effect when the orca grandmother becomes menopausal: non-fertile, she can then devote much more attention to her grandsons and granddaughters. With this new study, we measure the charge behind this effect. A burden that weighs on females, long before menopause, long before they become grandmothers.
And we’re a little tempted to extrapolate that to us humans…
Yes. Especially since the phenomenon of menopause has only been identified in three mammals: humans, killer whales and pilot whales – another cetacean. Especially since the “grandmother” effect was first observed in human societies. The killer whales here teach us that behind the benefits brought to children and grandchildren, there is always a cost. But this, the mothers and grandmothers already knew.