Menopause is when females stop producing mature egg cells, which is vital for successful reproduction. There are only 3 species in the animal kingdom that undergo menopause: humans, killer whales and short-finned pilot whales.
The reason behind why menopause happens isn't clear, but finding the common factor between these species may be the answer for this conundrum. Thus, observations gathered from killer whales may be the key.
A study published in Current Biology,
suggests that menopause may play a role in lowering the chances of reproductive conflict between mother and daughter killer whales.
Darren Croft, a professor of animal behavior at the University of Exeter in England and an author of the new paper, studied the killer whales' behavior. Together with his team, they learned that older killer whale moms have calves with higher mortality than the younger moms.
Killer whale groups are matriarchal, which means the mom's daughters and sons stay with their mother even when they have started mating. The killer whale moms thus gather more food for the family, also because they are more experienced than the young killer whale moms.
“When females are born, they have a relatively low relatedness to the males in their group, because their father isn’t around,” Dr. Croft told NY Times
. “But as a female starts to reproduce, her relatedness to males increases, because her sons stay with her.”
Experts' theory says that older killer whale moms may have stopped producing to help their daughters take care of their offsprings. Older killer whale moms may be helping with the babysitting, or by sharing knowledge to their daughters.
This resulted in the evolution of female killer whales. Though, they can live up to a century, female killer whales stop reproducing when they reached 30 or 40. As per expert's conclusions, menopause makes way for older moms to help their daughters, which usually start reproducing at age 15, to strengthen the survival of young calves.
The researchers added, though the family construction of killer whales is far different from human's, the reason behind menopause may be true for both species.