[examine the full size graphic at www.superscholar.org/shrinking-brain.]
In paying attention to the news nowadays one might be justified in discerning symptoms of a physical phenomenon baffling anthropologists and biologists. The human brain is shrinking in size. Brain size has decreased about 1500cc in the last 10,000 years. In other words, if our bodies shrank as much as our brains have are we would be on average 4'6" tall and weigh 64 pounds.* Whilst our brains are smaller our encephalization quotient, or the measure biologists use for a species relative intelligence, has leveled off. As a species we are not getting dumber irregardless of the behavior or our politicians, but we are not getting noticeably smarter either. Various hypotheses have been put forward to account for our ancestors' bigger brains. Evolution responds to efficiency, and brains are notoriously energy intensive. Brain mass is just 2% of the human body, but consumes 20% of its resources. Now that we no longer hunt mastodon or fend off cave bears at night, our brains have reduced less used circuitry such as that dedicated to vision. Social support from human society allowed individuals with smaller brains to survive and populate the gene pool. Reduced human aggression--hominid bones show signs of violent injury and physical stress--has led to prolonged juvenility which encourages domesticity. As one scientist put it, "the story written in our bones is that we look more and more peaceful over the past 50,000 years". Perhaps there is hope, afterall.
*Once, a race of giants lived amongst modern humans if the biblical record is accorded historical credibility. David killed Goliath according to the legend, but Goliath had a giant brother named Lahmi who was also killed by David's men writes the Chronicler. 1Chr 20. Still another "decendent of the Raphaim of Gath" was Sippai. Large in stature, they were also polydactyl. The Bible contains several references to tribes of giants. ("Nephilim" and "Anakim") Are these the last decedents of Cro-Magnon? (see relative brain size chart above).