Hypothetical populations that didn't age and die would have killed themselves off due to lack of food.
I'm sorry, that's 3000+ years where we know our longevity hasn't changed, especially considering all of these men entered warfare. People living to 100 with all their mental and physical strength is rare, however people living to their 60's is not and has never been.
Our genes evolved to fight childhood diseases and injuries, so that those who make it through have the potential to live well into their 60's without a problem. Incidentally, those who get sick less frequently in childhood tend to have a longer lifespan as is. However the whole notion that humans only lived till 30 is absurd, because it's simply not true for any of recorded history. Yes it was the average, however that was under a very different culture.
Ramesses II successor was his 13th son, who lived to his early 80's. Many of his other children either died very early or died through injury or mid-life disease. His first born for instance died from a blow to the head in his 40's.
Please, don't confuse life expectancy and longevity, the two are vastly different. The former has changed drastically, the latter hasn't. Regardless of whether we avoid disease today or 3000 years ago, we'll likely hit 90 years before dying of old age 'naturally' (IE from a lack of longevity).
I agree. That's the only mechanism that seems to have the power to explain aging, other than magic or the Invisible Hand of the Creator (but the latter two have a huge assortment of other issues).
A non- or post-reproducing individual can still improve the fitness of their genome by supporting closely related individuals, or even simply their species by supporting any other member.
Starvation is not the only way living creatures can die.
Just up the aggression a little, for example, and the death rate returns to a self-sustainable level.