Steven Pinker was saying that greatly extending the human lifespan is hard, maybe impossible: ” I suspect that death will never be conquered (though our lifespans will continue to increase, at least for a while). Any cost-free longevity gene or easily tunable molecular pathway would have been low-hanging fruit for natural selection long ago. Senescence is baked into most of our genome because of the logic of evolution: since there’s a nonzero probability at any moment that an organism will die in an unpreventable accident, making genes for longevity moot, selection tends to sacrifice longevity for performance at every level of organization. This means we’d have to know how to tinker with thousands of genes or molecular pathways, each a tiny (and noisy) effect on longevity, to make the leap to immortality. The low-hanging fruit is in fact at the other end of the lifespan and income scale. We’ve made massive global progress in reducing maternal and infant mortality and premature death, but we’re not seeing a cohort of billionaire centagenarians. ” Centenarians.
He’s got the argument backward: sure, natural selection has not favored perfect repair, so says the evolutionary theory of of senescence. If it had, then we could perhaps conclude that perfect repair was very hard to achieve, since we don’t see it, at least not in complex animals.* But since it was not favored, since natural selection never even tried, it may not be that difficult.
Any cost-free longevity gene that made you live to be 120 would have had a small payoff, since various hazards were fairly likely to get you by then anyway… And even if it would have been favored, a similar gene that cost a nickel would not have been. Yet we can afford a nickel.
There are useful natural examples: we don’t have to start from scratch. Bowhead whales live over 200 years: I’m not too proud to learn from them.
Lastly , this would take a lot of work. So what?
*Although we can invent things that evolution can’t – we don’t insist that all the intermediate stages be viable.