>Why hasn't evolution turned the dial up another couple of notches?
Because evolution doesn't care about us beyond reproduction age (after which is when most cancers occur, especially considering that historically that age was between say 16 and 35).
Or even better phrased, because evolution doesn't care or plan at all, it's a blind mechanism.
If a local minimum is ok, we'll stay there for as long as some environmental or other evolutionary pressure gets to move us further.
Cancer wasn't a big issue for most of our existance as species, especially with lower life expectancies, more active lifestyles, zero obesity, zero pollutants, etc.
In evolutionary terms, modern lifestyles are not even a blip, especially post-industrial ones which don't even register.
That's a very late specimen, and in fact one which "led scientists to speculate that he was involved in copper smelting", hardly typical of revolutionary timescales.
In evolutionary timescales, agriculture and permanent houses are a dot in the timeline, there were no longhouse dwellers for 95% of homo sapiens' history, and none at all for hominids before homo sapiens. They were nomadic foragers.
> Because evolution doesn't care about us beyond reproduction age (after which is when most cancers occur, especially considering that historically that age was between say 16 and 35).
This is the lie that needs. to die. Elder people were very important in even the most primitive societies. "lifespan" was low in pre-history, not because no one lived long lives, it was because infant mortality was very high.
Lie implies conscious distortion of the truth, the word you were looking for is "falsehood".
Second, even if "elder people were very important in even the most primitive societies", their role is much much important from evolutionary perspective than the pressures based on reproduction. Which is why most close primates get by with zero roles for post-reproduction grandparents.
Also elder people being "very important in even the most primitive societies" is a cultural and recent in evolutionary timescale phenomenon, first and only secondarily an evolutionary one.
> "lifespan" was low in pre-history, not because no one lived long lives, it was because infant mortality was very high.
They also lived shorter lives to begin with. Even in later historical times (say a couple of millenia or so), people's life expectancy at 15 (meaning, with infant mortality excluded) was much shorter than today.
Nobody said that "no one lived long lives" however. Some did. It's an aggregate limitation, not an absolute one.
Not disagreeing at all that elders are and have been important, but if it’s a benefit after reproductive age where does the selection come in?
I’m open to ideas. The only one I’ve been able to come up with is more second-order: the genetic benefit could come from having your children also pass on your genes, if there was a higher probability of them doing that with their parent alive past reproductive age.
"Bitch" by Lucy Cooke has a chapter dedicated to this if you're interested. It's pop sci but a great read and offers some new perspectives.
Menopause seems to be a biological adaptation to this - most mammals don't have it, they'll keep on having young until they're totally exhausted, and die not long after. Humans seem to be adapted so that women have a wild-type generation's worth (15-20 years) of useful lifespan post fertility.
> Because evolution doesn't care about us beyond reproduction age
I wonder if that's true. There's bound to be some benefits or drawbacks to aggregate fitness when people age. Sure, the contribution is very indirect and so it'll happen yet slower. But imagine if people lived until they were 300 years old. Depending on how frail they are, that could be a drag on reproduction and resources.
>The benefits and drawbacks that appear after reproduction age can’t be passed on.
If we consider grandparents, they could.
E.g. more fit/older grandparents -> more help and experience sharing for raising the kids given to the parents, more infants survive. This would chose for lineages where grantparents are helpful && live more.
What I meant though is that the main evolutionary pressure of us in in reproduction. Sure some past-reproduction-age traits play a role, but hardly as big.
> Because evolution doesn't care about us beyond reproduction age (after which is when most cancers occur, especially considering that historically that age was between say 16 and 35).
True. If we can find a drug or gene therapy that extends the reproductive age of humans, evolution will take care of all diseases in a few million years, give or take.
Could be a cliff fitness function. Heard about this relativ typ schizophrenia here on HN a while back. The idea is that some phenotypes promote survival of the species overall, but due to random mutations are sometimes detrimental to individual members of that species
It could also be indirectly linked to other benefits. Humans have lost the CMAH gene, making us able to run long distances and hunt down large prey animals. But because of this we can no longer process specific sugars that you will still find in mammalian meat. That causes inflammation and arteriosclerosis. But those things only kill you after many decades, so there seems to have been a net positive effect on evolution.
This idea can generally work, but one should be careful of 'just-so' stories in evolutionary biology.
It appears this deletion happens in other animals and may be attributable to pathogen pressure. It's arisen multiple times, which makes it hard to claim that it has a specific role in primates (beyond its presumed antimicrobial benefit, which any animal should enjoy).
Evading pathogen pressure is just another benefit behind the scenes. The point is that I would be careful to attribute any of these things to such weird mechanisms when there are so many much more realistic explanations that we just haven't fully uncovered yet.
> Evading pathogen pressure is just another benefit behind the scenes.
I'm imagining that this relates to a specific pathogen that may no longer exist (like the presumed mechanism of the most common cystic fibrosis mutations and cholera).
I'm not sure how this would relate to humans running, however.
Perhaps, but AFAIK similar things show up in other metabolically "different" animals - sharks, naked mole rats - whereas rodents adapted to a "run hot and fast" kind of a lifeplan seem to be especially prone.
We know that the body has cancer suppressor mechanisms, because when they fail (due to HIV or genetic mutations) people suffer higher rates of the disease. So it's reasonable to guess that evolution has chosen not to dial them up further.
It feels like the immune/inflammatory system is something we understand about as well as the brain, which is to say pretty good at a gross anatomical level, and also at the fine molecular level, but with a heck of a lot of complex system dynamics in between remaining to be mapped out.
Put it another way, it seems our systems are balanced to regulate cancer during our youth and reproductive years to a low but non-zero level.
Why hasn't evolution turned the dial up another couple of notches? Could be simple metabolic cost, or could be something else.