This is the third post, with maybe one more to come, to look at the "grandmother effect," in which human grandmas who are past their childbearing years can nevertheless contribute to the propagation of their genes indirectly by taking care of grandkids. The first post is here and the second post is here . This post is much more speculative.
What interested me when I first read about the grandmother effect was the possibility that human evolution had taken us (via the disposable soma ) out of the birth-reproduction-death treadmill and instead we as a species (or at least the females among us) were "programmed" for an extended, extragenetic-- probably social and cultural-- contribution to the species. This is probably true anyway, but more specifically, I was looking for some hint that humans would be capable of extreme longevity. I'm interested in long-lived cognitive function, and I have to emphasize that the rest is outside my expertise. With that said, I think the idea of greatly extended lifespans looks unlikely.
Among the killers of humans today are cancer, cardiovascular disease and dementia. These all start as failures of a specific system. One possible way to extend the average lifespan would be to plug holes-- to attack these diseases as they emerge, so that a major disease is delayed or the faulty part replaced, ab infinitum. An enthusiastic proponent of this approach (combined with other strategies) is Dr. Aubrey de Grey who pops up in the major media every now and then talking about lifespans on the order of centuries. De Grey's idea is that a mixture of delaying disease and replacing diseased tissue might allow great extensions. He was recently on the receiving end of a major smackdown for claiming that excessive pessimism on life extension by other gerontologists was costing lives .
So far, so comic. I guess what has me pessimistic about life extension by plugging holes is some very recent evidence that healthy tissue in elderly primates just gets worn out. A study in this week's Science shows that elderly captive baboons living develop sensescent cells in healthy tissues , suggesting that, well, they're getting old all over. Senescent cells were seen in vitro in skin and connective tissue cells, and were measured using three different measures. Moreover, the percentage of senescence went way up in cells from older animals. With a bit of extrapolation, you would guess that baboons of around 30 years of age are going to wear out in multiple places. Illnesses arising from this kind of senescent failure could not be fixed piecewise, and that makes me think that the lifespan of these animals is pretty near maxed out.
UPDATE: Aubrey De Grey is also written up in the Economist from last week.