Female orcas (killer whales) live into their nineties, even though they typically stop breeding at 40. Males only live to 50:
The only other species known to go through a menopause and live so long without reproducing are humans and short-finned pilot whales.
Croft and colleagues watched 750 hours of video of orca family pods. Over 100 individually recognisable orcas were filmed in the coastal Pacific waters off British Columbia and Washington since 1976.
The team found that post-menopausal females were 32 and 57 per cent more likely than non-menopausal adult females or adult males respectively to lead the group. They were also significantly more likely to lead the group in years when their staple food – chinook salmon – was in short supply.
“It’s probably accumulated experience,” says Croft. “Anyone who fishes for migratory trout or salmon will tell you that timing is key, that the fish return in particular cycles of tides and times of the year. Post-menopausal females probably get to know where to look and when.”
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In most known animal species, males rapidly leave their parents, becoming completely independent. Male and female orcas, by contrast, stay in a family unit for life, with the males occasionally exchanging pods temporarily to breed. The upshot, says Croft, is that if females survive for many decades, breeding for the first three or four, their pod becomes increasingly replete with their descendants. Therefore, it becomes more and more in their own interests to safeguard the survival of the pod, and thereby their own genetic legacy.
“There’s a tipping point where they stop reproducing and help their offspring instead, as do grandmothers in the human context,” says Croft.
The findings seem to support the “grandmother hypothesis”, the idea that older women in hunter-gatherer communities evolved to go through the menopause so that they could carry on passing on their wisdom and experience about food sources and other survival tips without the added costs of having more children themselves.
Please drop the da***d Lamarckism. Evolution occurs by pre-adaptation followed by an existential crisis in which the pre-adaptation proves beneficial for survival of the individual, e.g. bacteria aren’t evolving to have “drug resistance;” the population is shifting in favor of those who already have the resistance.
There’s nothing Lamarckian about saying that a population evolves in a certain direction.