Is the human race getting dumber? geneticist Gerald Crabtree thinks that human intelligence peaked several thousand years ago and from then on, has been on a slow decline.
His argument is based on the fact that for more than 99% of human evolutionary history, we lived as hunter-gatherer communities surviving on our wits, which led to the big brains we have today. Since the invention of agriculture and cities, however, natural selection on our intellect has stopped and mutations have accumulated in our critical "intelligence" genes. A comparison of the genomes of parents and children reveals that there are between 25 and 65 new mutations in the DNA of each new generation.