America's rousing success over the past two centuries may be going to our heads, Tennessee researchers say. A study of skull sizes with specimens ranging from the mid-1800s to the mid-1980s indicates that the average head size of Americans has increased during the period. The researchers are unable, however, to pinpoint a precise reason for the change, and are unsure whether it is due to evolution or lifestyle changes. But they noted that average heights are also increasing, and that has frequently been attributed to better nutrition and improved medical care.
Anthropologist Lee Jantz of the Forensic Anthropology Center at the University of Tennessee and his colleagues studied 1,500 skulls of Caucasian Americans. Jantz reported at a meeting in Portland, Ore., of the American Assn. of Physical Anthropologists that the skulls have become larger, taller and narrower as seen from the front, and faces have become significantly narrower and higher.
The team found that in men the average height of the skull from base to top has increased by 8 millimeters (0.3 inches) during the period, while the capacity has grown by by 200 cubic centimeters, about the size of a tennis ball. In women, the corresponding increases are 7 mm and 180 cc. That is a 6.8% increase in skull height, compared with a 5.6% increase in body height during the period and a 2% increase in femur length. Moreover, the researchers said, skull height has continued to increase, while body height has plateaued.