[williamkuszmaul]

Interesting post!

Small comment on the argument against anti-aging genes existing: "genes only propagate if selected for, and there’s no selective pressure for longevity after reproductive age" (I know that this was just a very minor aside, but I still think it's worth pointing out the flaw.)

That's not how evolution works. Even after you have reproduced, you have impact on whether your children survive and reproduce. This means that there could very reasonably be evolutionary pressure in either direction (causing people to die younger that way they stop taking resources from their children or causing people to live longer that way they keep providing support for their children).

[jhales]

It's also a factual error. There have been longevity genes discovered. Cynthia Kenyon famously doubled the lifespan of a C. Elegans by mutating daf-2: https://www.nature.com/articles/366461a0

[codeflo]

That’s plausible, but there might be trade-offs involved. There’s a theory — not sure how serious it’s taken by experts — that at least some of the mechanisms involved in aging have other benefits. For example, the fact that telomeres limit the number of cell divisions might also be a defense against cancer. A mutation that increases lifespan at the cost of this mechanism could be a net negative, from an evolutionary point of view.

[HPsquared]

This idea is called group selection [0].

Edit: perhaps kin selection [1] is the more appropriate one here.

Still, longevity would affect the group and not only the direct kin.

[0] https://en.m.wikipedia.org/wiki/Group_selection

[1] https://en.m.wikipedia.org/wiki/Kin_selection

[syllogism]

More like kin selection: https://en.wikipedia.org/wiki/Kin_selection

[skybrian]

Effect size is hardly ever zero and surprisingly small effect sizes can be measured. But is this evolutionary pressure large enough to make a difference for a longevity gene when people already live quite long after having children?

[pharke]

I think the idea is that there aren't "longevity" genes only aging genes. Put another way, aging isn't an accident caused by the accumulation of damage. It's a selected for trait, a sort of slow, whole body apoptosis used to get rid of the soma once it's served it's purpose. Lifespan is simply the well timed removal of a generation once it has had the opportunity to reproduce and raise its brood.

[codeflo]

I’m not sure I buy that completely. If this were a neutral choice, why would a gene take the 50% chance of not having made it to the next generation? (Or in the case of many offspring, invest half its resources into a different copy of the gene?)

At least in mammals, killing the soma is on the surface such a massive waste of resources that I believe it must be either: (a) biologically implausible to keep an animal reproducing for a longer timespan or (b) caused by mechanisms that are counterweighted by massive reproductive benefits while the animal is young.

[pharke]

> killing the soma is on the surface such a massive waste of resources

How is it a waste of resources? Evolutionarily, the goal is to produce another successful generation who then begets another generation and so on. The rate at which that happens is a balance between what is necessary to confer the best chance of survival to each child, the number of children needed to outweigh the mortality rate, and the required mutation and crossover to adapt to the environment. Keeping the same individuals in circulation longer doesn't confer an advantage to their offspring since they already posses the same genes. It would more likely hinder the propagation of their genes by taking resources away from their progeny and competing for mates, territory, status, whatever.

[robwwilliams]

Perfect! And reproductive longevity is strongly selected. Mole rats and bats, despite small bodies and quite high metabolic rates live far longer than might be expected from simple allometric relations. Reproductive lifestyles can evolve by bootstrapping on large numbers of DNA variants that modulate and molecular-cellular systems.

[pyrrhotech]

Also simply because there is no selective pressure for a gene does not mean it does not exist through pure chance.

[jakear]

The balance point being to live to provide care to the grandchildren while the children are in the height of their career, then die off in order to free up resources?