Not exactly, but which part are you referring to? I just made the assertions by thinking through our history from stuff I've read before and putting myself in the shoes of people in the distant past. Life was absolutely brutal in the past and I think we're all incredibly lucky to live in the time that we do now.

Oh it was brutal and we are lucky. That does not mean people were depressed and anxious back in the hunter-gatherer-tribes era. I always thought depression and anxiety were rather modern ailments.

It's a guess, but I would imagine life back then where there was constant danger from predators and other tribes would be similar to the lives of soldiers in combat now. I'd guess that ptsd isn't a new invention and that barely surviving an attack could scar individuals.