I learned an intriguing fact while watching the PBS documentary series First Peoples: the human brain has been shrinking for at least the last 10,000 years. We may be dumber than our distant ancestors.
A big brain confers the evolutionary advantage of higher intelligence, but it also comes at a high price. For creatures who walk upright and have a pelvis adapted to the task, big heads are hard to birth, contributing to peri-natal maternal and child death. Natural selection has favored smarter populations, but only as smart as necessary. Intelligence might be limited because the size of larger heads presents an unacceptable death rate.
So why have selective pressures been reducing the size of our brains precisely at the time when we see the evidence of our intelligence? This article poses several explanations. The change may be result of an overall reduction in body size, due an increase in global temperatures that began at the end of the last ice age.
Another theory is that we no longer need quite so much brain power because we've externalized our knowledge through culture. Twenty thousand years ago, a human being performed most survival functions for him/herself. A nomadic hunter/gatherer had to remember the daily waypoints for long migratory routes from one year to the next, master hunting and food rendering techniques, identify which plants in the seasonal environments were edible and which were poisonous, evade predation, establish shelter, and navigate the complexities of fluid relationships between nearby clans.
Now, we have outsourced most of our survival expertise to others through specialization. Each of us is no longer obliged to know the details of butchery and food production. Where we were once walking libraries of information, we now have libraries - virtual and actual, which sit outside our minds, and support them like informational prostheses.
Maybe we no longer need the brain power we once had, back when it made the critical difference in our survival. But it's a little disconcerting to think we might not possess the smarts of people who walked the earth before we mastered farming or metallurgy. It feels like we could use the help of a few extra IQ points right now.