menopause in other mammals

I just saw on tv the other day that, aside from homo sapiens, the only animals to experience menopause are killer whales and pilot whales. This is an odd triad of species. Why should it be so? All are intelligent, all are social, but if those are the criteria, shouldn’t all the other primates have menopause as well as all the other whales?

I’ve heard several theories about human menopause. Some people think it is a recent phenomenon–that most women simply didn’t live that long until recently (in evolutionary terms). Others have speculated that it is valuable to have healthy but non-breeding women around to work and help take care of young children, etc. (This is certainly borne out by many human societies, but that doesn’t mean it’s genetically programmed.)

I think it would be really tricky to theorize about the natural selection of something like menopause, though, since it happens AFTER the individual’s reproductive life. Unless it somehow helps or interferes with the survival of a woman’s (or a whale’s) offspring, it may just be an artifact that really didn’t “evolve” for any particular purpose.