Humans never needed to be hyper-adaptive. 80+% of people in the far past were farmers their whole life, just like their parents, and their children, and everyone they associated with. Prior to farming, dumber means of food gathering. You worked your ass off or died but it was never about the latest thing, that's a purely modern invention. Hardly anybody went to "school" or learned a trade, nobody expected job changes every 5 years. You were a dirt poor, uneducated, worn down farmer. The modern invention was the idea we'd have time to be something else and the very recent invention is that you'd need to be multiple something elses over time.