Well this is a cheery thought -- human intelligence "peaked thousands of years ago and we've been on an intellectual and emotional decline every since":
His argument is based on the fact that for more than 99 per cent of human evolutionary history, we have lived as hunter-gatherer communities surviving on our wits, leading to big-brained humans. Since the invention of agriculture and cities, however, natural selection on our intellect has effective stopped and mutations have accumulated in the critical “intelligence” genes.
“I would wager that if an average citizen from Athens of 1000BC were to appear suddenly among us, he or she would be among the brightest and most intellectually alive of our colleagues and companions, with a good memory, a broad range of ideas and a clear-sighted view of important issues,” Professor Crabtree says in a provocative paper published in the journal Trends in Genetics.
In other words, we no longer have to fight to survive, so "survival of the fittest" no longer applies. I had a science teacher in high school who took that kind of argument about as far as it could go. Even those of us with only mild defects -- like eyeglass wearers -- were contributing to the decline of the race, in his opinion. After all, natural selection declared that nearsighted mopes would be killed by approaching wild animals they couldn't see, so perfect vision would become the norm. Or something like that.
Most of us have thought from time to time that historical figures seemed intellectually suprior to the current crop of deep thinkers. Can anyone image a group like those who met at the constitutiomnal convention could ever be assembled today? It's a little disheartening to think the reason might not be general cultural entropy as is usually argued but, rather, the natural result of us having developed as much as we can.