SALT LAKE CITY — Americans' heads are getting bigger — literally.
A new study by researchers at the University of Tennessee, Knoxville, found that some Americans' heads have grown larger over the past two centuries.
Forensic anthropologists at the university studied 1,500 skulls dating back to the mid-1800s to the mid-1980s. The researchers found that caucasian American skulls have grown larger, taller and more narrow as time has passed. Caucasian American faces have also become significantly higher and more narrow, according to the university.
The average height of the skull has increased by nearly one-third of an inch, and skull size has grown by 200 cubic centimeters in men and 180 cubic centimeters in women — about the size of a tennis ball.
The increase in skull height is not proportional to other increases in American body size. Skull height has increased by 6.8 percent since the late 19th century and continues to increase. Body height has increased by 5.6 percent in the same time period, while femur length has increased by only 2 percent. Both body height and femur length changes have slowed or stopped in recent years, though.
The team also found evidence of Americans maturing earlier in life. A separation in the bone structure of the skull was once thought to close at about age 20. In the skulls studied, the gap had fused at age 14 for females and at age 16 for males.
Researchers are unable to explain the changes, due in part to the large amount of changes that American life has seen since the 1800s, according to Lee Jantz, coordinator of the school's Forensic Anthropology Center.
The country's obesity epidemic could play a role in determining future skull size.
"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," he said. "Which of these is paramount we do not know."
The country's obesity epidemic could play a role in determining future skull size by changing the body's hormonal environment, according to Richard Jantz, the center's former director.
Nearly 36 percent of American adults and 17 percent of Americans age 19 and younger are obese. Obesity is already known to increase arthritis in certain joints, increase weight-bearing capacity and increase muscle attachment areas.
"This might affect skull shape by changing the hormonal environment, which in turn could affect timing of growth and maturation," Richard Jantz said.
Changes in the skeletal structure are taking place in many areas of the world, according to the researchers, but tend to be less studied. For now, it is unknown what the impact of the changes will be.
