Killer whales need their mamas to look after them... even as adults

Despite their fearsome nickname, orcas might actually be among the animal kingdom's biggest mama's boys. Males rely on their mothers to keep them alive well into their adulthood — and that might help explain the evolution of menopause.

Killer whale females can live as long as fifty years after when they produce offspring in their thirties. That long span of post-reproductive life sounds similar to the human experience, but it's otherwise a fairly rare occurrence in the animal kingdom. It's the sort of thing that is unlikely to occur unless there's a solid evolutionary advantage driving it. And the big survival benefit for long-lived females is the survival of their sons to breeding age.

That's the finding of new research from the University of Exeter. Study leader Dr. Darren Croft explained to the BBC just how big an effect a mother's death has on an adult Orca male, and how the fact that Orca young never leave the care of their mothers might be driving it:

"Our research shows that, for a male over 30, the death of his mother means an almost 14-fold-increase in the likelihood of his death within the following year....With this close association, older mothers have the opportunity to increase the transmission of their genes by helping their adult offspring survive and reproduce. We simply don't know just how mothers are increasing the survival of their adult male offspring. Anecdotal observations suggest that mothers may help adult sons with foraging or providing support during aggressive interactions. This is one of the things we hope to work on in the future."

And this does appear to be a males-only phenomenon — adult females only experienced a three times greater likelihood of dying within a year of their mothers' death, while female young saw no increase in risk of death at all. That might suggest further support for the idea that male-specific behavior requires long-term support from mothers, with the violent fighting over mates an obvious candidate for an explanation. Whatever the exact reason, orca males have given their mothers a good reason to keep on living long after their reproductive duties are completed, and that means we're looking at an evolutionary mechanism that can explain menopause. Of course, whether all this can help explain menopause in humans is probably best left for another day...

Via BBC News. Image by DrTH80 on Flickr.