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The long lifespan of whales could actually shed some light on human evolution. Whales, along with many other mammalian species (including humans) exhibit a per
by samizdatum 13y ago
The long lifespan of whales could actually shed some light on human evolution.
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.
- has2k1 13y agoA convenient theory for longevity is, late menopause implies a selection (in the history of the species) against all of forms early age killers. So, I find it fascinating that a warm blooded (or even cold blooded e.g turtles) animal with an early menopause can ward off cancer for that long.
- rthomas6 13y agoThis is a bit of a stretch, but perhaps if whales are as smart as we think they are, elders are advantageous because they can pass down wisdom to younger whales.
- mhartl 13y agoYour suggestion is essentially the "grandmother hypothesis" mentioned in the parent comment.
- nollidge 13y agoAnother strong possibility is that it's not a selective adaptation at all.
- maaku 13y ago> 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. I thought average life expectancy of per-agrecultural, pre-technological humans was less than 40 years? It doesn't really seem like the grandmother hypothosis would enter into our evolutionary history then, as there would be very few post-menopause grandmothers around...
- jeorgun 13y agoAverage life expectancy is calculated without accounting for infant mortality; when accounted for, it's considerably higher, or so I'm told.
- crpatino 13y agoEven if infant mortality is discarded, average life expectancy is a poor estimator of typical expectations of life. Considering the case of pre-industrial societies, there was a second big wave of mortality during what we now call adolescence. In women it was driven by child bearing, while in men by either accidents or armed conflict with other groups of men. If half of the guys that make it to their 13th birthday will get themselves killed before their 21st, an average of 40 y.o. gives a very misleading idea of what "old folks" look like.
- CWuestefeld 13y agoaverage life expectancy Age at death has a bimodal distribution: a huge portion of humans die at or near birth. If you survive that you're pretty likely to live quite a while, living well past the mean. That's 'cause all the deaths at infancy bring down the mean quite a bit.
- gnaritas 13y ago> I thought average life expectancy of per-agrecultural, pre-technological humans was less than 40 years? Bill Gates fortune and mine average about 33 billion; averages aren't always useful information.