Years ago I read a paper by Hillard Kaplan, a University of New Mexico anthropologist, about the evolutionary economics of brain size. I tried to do a story, but he was off in the jungles of Bolivia working, and we never connected. Cleaning out a file recently on my desk at work, I came across the paper, and called him. Here are the results:

Consider the fundamental difference between us and our nearest living relative, the chimpanzee.

The typical adult human brain weighs 3 pounds.

The chimpanzee's brain weighs 1 pound.

The difference, according to Kaplan, a UNM anthropologist, is a matter of economics. Think of that big brain as an investment. It takes a while to build, with mom and dad kicking in most of the up-front costs.

Once built, it takes a long time to take advantage of it— to learn the intricacies of finding one's way along a faint jungle trail, for example.

"Children are net consumers all the way up to age 20," Kaplan said.

In the long run, the payoff is huge. The knowledge gained in the lengthy period of tutelage makes grown humans remarkable economic engines, whether in the jungles of Paraguay or a modern technological society.