Americans’ heads are getting bigger

Americans' heads are getting bigger

The heads of Americans are changing – and rapidly – skulls are getting bigger and faces are getting longer and narrower.

Within just 150 years, American heads have grown in volume by roughly the volume of a tennis ball The survey of 1500 skulls compared skulls from the mid-1800s to skulls from the Eighties – and the shape is definitely changing.

Are Americans evolving? The researchers don’t know – the changing head shapes (found in samples of white Americans) could also be due to better nutrition or racial mixing.

‘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.’

The researchers found that the average height from the base to the top of the skull in men has increased by 0.3 inches. The skull size has grown by 200 cubic centimeters, a space equivalent to a tennis ball. In women, the corresponding increases are seven millimeters and 180 cubic centimeters.

Skull height has increased 6.8 percent since the late 1800s, while body height has increased 5.6 percent and femur length has only increased about 2 percent. Also, skull-height has continued to change whereas the overall heightening has recently slowed or stopped.

The scientists also noted changes that illustrate our population is maturing sooner. This is reflected in the earlier closing of a separation in the bone structure of the skull called the spheno-occipital synchondrosis, which in the past was thought to fuse at about age twenty.

Richard Jantz and Natalie Shirley, an adjunct assistant professor in the FAC, have found the bone is fusing much earlier — 14 for girls and 16 for boys. America’s obesity epidemic is the latest development that could affect skeletal shape but its precise effects are unclear.

‘This might affect skull shape by changing the hormonal environment, which in turn could affect timing of growth and maturation,’ said Richard Jantz. ‘We know it has an effect on the long bones by increasing muscle attachment areas, increasing arthritis at certain joints, especially the knee, and increasing the weight bearing capacity.’

The research only assessed Americans of European ancestry because they provided the largest sample sizes to work with.


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