White Americans are the head and face were the changes in the shape of the average, and no one knows quite why, according to new research.
In the trend may be determined by going back to the mid-1800s, the U.S. got more skulls, higher and narrower, as seen from the front, said Richard Lee Jantz, a husband and wife team of forensic anthropology at the University of Tennessee, Knoxville. They also found that people are much narrower and higher, although this transition is less pronounced than those that affect the entire skull.
The changes going on in the generation born in the 1980s, where they come from the latest research for the skull, according to Jantzes, who presented their findings April 14 at the annual meeting in Portland, Oregon American Association of Physical Anthropologists.
"I have no reason to believe" the changes stopped, said Richard Jantz in an interview.
He referred to a sharp increase in food availability, higher quality health care and reduce child mortality, as possible factors behind the changes, but expressed pessimism that the final cause can be identified. A large number of changes that have swept American life, making it "infinitely complex" proposal, he said.
"We live in an environment that is quite different from the one that has ever existed in the past. It's like putting the experimental animals in extreme conditions."
Big head may allow more intelligence, but it is unclear whether the increase is associated with improved intelligence, Jantz said. Some aspects of changes in the shape of the skull is not always healthy. Earlier puberty, which has led to reports of girls get pregnant before adolescence, may be reflected in the previously closed in the youth section of the structure of the skull called the occipital synchondrosis spheno-,
he said. America's obesity epidemic is the latest development, which can affect the skeletal form, Jantz said, but its exact effect is uncertain.
Although changes in the structure of the skull may be more likely to go on, "they do not have to continue in the same direction," he added.
Studies were assessed only Americans of European descent, because they provided the largest sample size for the job, said Jantz. More than 1,500 skulls were included in the study, many of whom came from the collection donated to the University of Tennessee.
The average height from the bottom to the top of the skull in men increased by 8 millimeters (0.3 inches), Jantzes found a skull the size grew to 200 cubic millimeters, the space is equivalent to a pair of small peas. In women, the corresponding increase of 7 millimeters and 180 cubic millimeters.
Changes in the structure of the skeleton occur in many parts of the globe, not just the U.S., Jantz said. But they are generally less well studied in other countries, except for the well-documented increase in the human growth of industrialized countries over the past century. "From what we know in Europe there are some" changes in the shape of the skull, Jantz said, but "not as dramatic as seen in the U.S."
Jantz tends to focus on lifestyle as a principle reason for change, not human evolution, although he said he did not exclude the other. The trend in the shape of the skull "keeps track of calories available to pretty much" in industrialized countries, he said.
The observed increase in the height of the skull, to some extent part of the total documented an increase in whole-body growth. But Jantz found that the height of the skull is not significantly increased in proportion to other parts of the body, and continues while the general worsening of slowed or stopped in recent years.