Anthropologists who examined 1,500 skulls dating back to the mid-1800s noticed one trend: American heads are getting bigger.
The researchers cannot pinpoint a reason as to why American head shapes are changing and whether it is primarily due to evolution or lifestyle changes.
"The varieties of changes that have swept American life make determining an exact cause an endlessly complicated proposition," said Lee Jantz. "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."