Well, by definition, we’re all just speculating here - obviously. I’m just speculating that man’s most important predator was other men. And that that would account for the findings in the article.
I guess *another* reason why I think that I’m right is that something changed 30,000 years ago. So what would that change have been? Tigers didn’t all of a sudden get more friendly 30,000 years ago. Bacteria didn’t all of a sudden get less virulent. Etc. etc.
But what could (and I would argue did) change 30,000 years ago was human social structures and arrangements. For all sorts of reasons early humans may have changed their social model, their economic model, technology may have changed etc. etc. and for some reason or combination of reasons 30 year olds stopped getting dispatched in steel cage death matches or ostracized from the group and left to starve but instead started being kept around for various reasons.
I guess having said what I just said that it could be they were killed off by other humans OR it could have been that they were cast off by the group and left to starve or be klled.
So pre 30,000 years ago it could be when you turned 30 you were killed by other humans or it could be you were abandoned by the tribe. Either way, you were done.
Then something changed and you were kept around and allowed to survive.
My point is that if 30 years old was a death sentence 40,000 years ago but wasn’t 20,000 years ago it was likely do to a change in the ways early humans self-organized and not due to the ability to outrun the tiger.
I do think you are on to something with the socialization idea. They may have gradually realized that there was safety in numbers. Groups can gather more food, evade predators better, and fight battles with enemies more successfully than individuals. That seems like common sense to most of us but there was likely a learning curve for early man. In a group setting it is generally the elders that mentor the younger members, so older members would have been valued more than in the past. Groups have many tasks that have to be done by someone, so weaker members would have been able to contribute something and would likely have been valued more for that reason.