A study has shown that only females in two species of Whales and Human experience menopause. The study by Scientists at the Universities of Exeter and Cambridge found that killer whales, pilot whales and humans are linked as only they have grandmothers.

According to the research, the Females become interested in and helpful for their grandchildren. This thesis was fist put forward during the 1950s. It said that menopause that stops female's fertility may be due to the important role grandmothers play in taking care of their offspring.

Dr Michael Cant, from the University of Exeter and the one of the authors explained, he along with Rufus Johnstone, Department of Zoology at the University of Cambridge looked into how humans and whales balanced "the costs and benefits of breeding with the costs and benefits of switching off breeding".

"It's easy to forget about the cetaceans, but since they're the only other mammal apart from us have a comparable post-reproductive lifespan, it's important to study them in this context," said Johnstone

“This isn't likely to be the only factor relevant to the evolution of ''grandmothering'' and menopause, but it does give us an idea why it is restricted to so few species in the animal kingdom," he added.

The duo developed a mathematical model to study "kinship dynamics" in killer whales, short-finned pilot whales and humans which showed that post-menopausal females developed closer ties with their grandchildren.

"Our analysis can help explain why, of all long-lived social mammals, it is specifically among great apes and toothed whales that menopause and post-reproductive helping have evolved," they said.

The report is published in Proceedings B of the Royal Society journal.