American Heads are Getting Larger

On the coat tails of Matt Ridley’s statement that humans are no longer evolving, comes news presented at last month’s annual meeting of the American Association of Physical Anthropologists that the heads of white Americans are getting bigger. Lee JantzRichard Jantz  and Joanne Devlin, took about 1,500 skulls dating all the way back to the mid-1800s through the mid-1980s.

Andy Warhol by Istvan Laszlo
Andy Warhol by Istvan Laszlo

What they observed is year-by year the heads of this sample are growing in volume. The skull of the average male human has grown in height by 8 millimeters and in volume 200 cubic centimeters. In women, the corresponding increases are seven millimeters and 180 cubic centimeters. This increase in volume is about the size of a tennis ball!

An even more unique result is the disproportionate growth of the skull compared to the rest of the body. Since the late 1800’s, skull height has increased 6.8%. But body height has increased 5.6% and femur length has only increased about 2%. Where skull height has continued to change whereas the overall heightening has recently slowed or stopped.

Lee Jantz tells that they cannot pinpoint a reason as to why American head shapes are changing and whether it is primarily due to evolution or lifestyle changes, but do note that,

“The varieties of changes that have swept American life make determining an exact cause an endlessly complicated proposition. It likely results from modified growth patterns because of better nutrition, lower infant and maternal mortality, less physical work, and a breakdown of former ethnic barriers to marriage. Which of these is paramount we do not know.”

Americans of European ancestry where analyzed here because of the large sample size and ease of accessibility.. Richard Jantz mentioned that in skeletal structure are occurring elsewhere but tend to be less studied, such as changes in European skull, though it is not as dramatic as this sample.

5 thoughts on “American Heads are Getting Larger

  1. No controls nor comparisons, right. Because one could imagine many reasons from growingly proteinic nutrition to adaption to intellectual competition through life (beginning in school), passing through variations in sources of immigration (a major source of US citizens in most of that period) or whatever else. The changes could be genetic or (more probably) environmental/epigenetic (which is nevertheless weakly heritable). The datum is there and is interesting but how do we explain it?

  2. Changes in diet, farming methods and Increased food intake may play a large part in this. We’re all heading (pun intended) towards crystal skull shaped heads!

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