[WhiteSage]

Auditory hair cells in the inner ear -the ones that allow us to hear sound- do regenerate in many animals but this mechanism fails in mammals. The surrounding cells try to replace them but something goes wrong and they die. This is why hearing loss is permanent, and exemplifies how stupid evolution can be at times.

[agent008t]

Are there estimates of how long it would take for humans to evolve to regenerate those cells - if specifically selected for it? Are we talking thousands of years, hundreds of thousands of years, or are there likely people alive today already that have the necessary mutations?

[WhiteSage]

I'm no expert, but there are many papers from 10 years ago where they identified a signaling gene whose concentration was not being raised enough for the neighboring cell to divide and replace the hair cell, and it was claimed that in 10 years hearing loss would have a cure. We seem to be more or less at the same point though, because it is not clear what goes wrong in the signaling pathway, or whether if that is the only issue. IMO too little is known to answer your questions.

[saiya-jin]

Evolution, AFAIK is just a random mutations happening here and there. If they bring some advantage (which good hearing in later age definitely should, but then again it covers mostly later age), harshness of life should eventually select those individuals as better survivalists.

Apparently whatever mutation happened in the past in this regard was not good enough / human still didn't survive, or it didn't happen yet. It might be funny if we discover some remote tribe actually has this regenerative mutation.

I think its question of time (maybe very long time), look at our unique ability to process lactose in adult age.

[close04]

Anything that happens after the end of an individual’s reproductive years (perhaps also the period of raising the offsprings) stops exerting any evolutionary pressure. The fact that you have a “defect” at old age no longer blocks you from transmitting it so it can propagate through generations without evolution selecting against it. Random mutations “fixing” the gene can occur but still have to compete with the overwhelming number of non mutated “defective” genes.

[7j]

> Anything that happens after the end of an individual’s reproductive years (perhaps also the period of raising the offsprings) stops exerting any evolutionary pressure.

This is definitely wrong. Individuals (e.g. grandparents or just random society members) can influence survival rates of other society members.

Some species(e.g. ants) even have sterile members that definitely exert evolutionary pressure.

[close04]

I think you didn't take enough time to understand my point before being so "definitive".

Sterile ants do not exert evolutionary pressure unless they would attack weak queens before they are ready to reproduce. Evolutionary pressure (by scientific definition) is caused by things that reduce reproductive success in individuals or parts of population. Like a mutation that reduces fertility. Having the old individuals around might help relieve some of the pressure by infinitesimal amounts (helping raise offsprings) but that's about it. They cannot influence the outcome of a "defective" gene so they do not really drive evolution in any meaningful way.

Take this example. A genetic disorder that causes blindness soon after birth basically eliminates the individual from the population and the genetic defect along with it. Thus evolutionary pressure (genetic defect before the reproductive age) achieves the selection.

A genetic disorder that causes blindness at old age, any time after the next generation was raised, might also eliminate the individual but this doesn't matter as much. The gene already got passed along to the next generation(s). As long as it manifests only after reproduction then it does not reduce reproductive success, so exerts no pressure.

Or perhaps you want to take something like male impotence as an example. If humans were expected to bear offspring only in our 70s I'm certain Viagra wouldn't be a thing. Only the males that are still able to perform at that age pass along their genes, to the point where the males that can't are the exception.

I hope you can appreciate the difference in magnitude (many orders) between directly applying evolutionary pressure by removing the individual from the gene pool before the gene can be transmitted, and indirect evolutionary pressure via reduced support in society (which could conceivably affect reproductive success). For one, it stands to reason that solitary species or ones that do not form real societies would be completely unaffected by this indirect evolutionary pressure.