Darren Croft from the University of Exeter here in the UK, along with colleagues, has found evidence to suggest that the menopause may have evolved in female orca so that they can continue to care for their adult sons! It may be a way of allowing a mother to invest her energies into the survival of her adult (male) offspring.
"There's some suggestion from whale watchers that they may guide their sons' foraging for food such as salmon, or provide support for their sons in aggressive encounters with other orcas," says Croft, theorising how menopausal orca may help their sons.
The researchers suggest the menopause may have evolved because protecting sons instead of having further offspring may give orcas the best chance of ensuring they pass on their genes.
Check out this New Scientist article for further information:
Here is the link to the Center for Whale Research Foster et al. (2012) paper just published in Science entitled: Adaptive Prolonged Postreproductive Life Span in Killer Whales.
Listen to the free Science podcast which talks about this research into orca menopause, with an interview from Exeter University's Emma Foster who led the project (http://www.sciencemag.org/content/337/6100/1365.2.full).