Whales, along with many other mammalian species (including humans) exhibit a perplexing divergence of somatic and reproductive senescence. Female whales hit menopause long before their lives are over, in some cases spending the majority of their lives in a non-reproductive state, which prima facie seems rather maladaptive.
A number of hypotheses have been proposed to explain what seems like widespread evolutionary selection for menopause, and none of them are completely satisfactory. The "grandmother hypothesis", for example, posits that experienced grandmothers assist in the care of their grandchildren, increasing their odds of survival.
Certain species of whales, including Orcinus orca, the killer whale, exhibit early-life menopause, and form stable matrilineal groups, making them ideal candidates for testing the grandmother hypothesis. Interestingly, studies on killer whales observe no significant correlation between living grandmothers and grandoffspring survival rates, though there are plenty of unaddressed confounding factors.
Humans are the only species where the grandmother hypothesis is supported by data, but the dearth of corresponding data in whales suggests the dramatic disparity in our somatic-reproductive senescence might be more strongly selected for by factors we are not yet aware of.