This is a curious observation that head size is increasing at a
faster rate than overall body size over the past century. My
interpretation of this observation is that we are predisposed to a
larger skull provided our bodies are large enough. Our cousin the
neanderthal had a relatively larger skull on a much more robust and
larger body. Thus the assumption of a simple linear relationship
could well turn out to be completely misplaced.
A number of factors have brought about larger Americans and this
trend is now developing everywhere. It starts with ample nutrition
but also the age of first pregnancy which has undergone a revolution
in the last generation.
Final maturation generally concludes in one's mid twenties whatever
may be claimed here and that is hardly changing.
I think that what is emerging is our natural optimized body and that
the process for some lineages is almost complete but most are
involved in catch up. If we could also optimize our diet, all would
be good.
University of
Tennessee anthropologists find American heads are getting larger
by Staff Writers
Knoxville TN (SPX) Jun 05, 2012
White Americans' heads are getting bigger. That's according to
research by forensic anthropologists at the University of Tennessee,
Knoxville. Lee Jantz, coordinator of UT's Forensic Anthropology
Center (FAC); Richard Jantz, professor emeritus and former director
of the FAC; and Joanne Devlin, adjunct assistant professor, examined
1,500 skulls dating back to the mid-1800s through the mid-1980s.
They noticed U.S.
skulls have become larger, taller and narrower as seen from the front
and faces have become significantly narrower and higher.
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."
The researchers found
that the average height from the base to the top of the skull in men
has increased by eight millimeters (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. Richard Jantz said changes in
skeletal structure are taking place in many parts of the world, but
tend to be less studied. He said research has uncovered shifts in
skull shape in Europe though it is not as dramatic as seen in the
U.S.
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