According to paleoanthropologist John Hawks at the University of Wisconsin at Madison, the human brain has shrunk roughly 10 percent over years of evolution, as a result of the changes in the human genome. LiveScience reports:
Surprisingly, based on skull measurements, the human brain appears to have been shrinking over the last 5,000 or so years... "As to why is it shrinking, perhaps in big societies, as opposed to hunter-gatherer lifestyles, we can rely on other people for more things, can specialize our behavior to a greater extent, and maybe not need our brains as much", he added. [emphasis mine]
Perhaps, but I have a different take on the root cause of our shrinking brains. It's written in the Book of Genesis, actually. When did man create god... oops, sorry... god create man? About 5000 years ago, give or take a few centuries. Surely, it cannot be a mere coincidence that the human brain started to shrink ever since, can it?
Who would need brains after there was religion?