"Long before it's in the papers"
June 04, 2013

RETURN TO THE WORLD SCIENCE HOME PAGE


American head shapes have been changing, but why?

May 14, 2012
Special to World Science  

White Amer­i­cans’ heads and faces have been chang­ing in shape on av­er­age, and no one knows quite why, ac­cord­ing to new re­search.

In a trend that can be iden­ti­fied go­ing back to the mid-1800s, U.S. skulls have got­ten big­ger, taller and nar­rower as seen from the front, said Rich­ard and Lee Jantz, a husband-and-wife team of fo­ren­sic an­thro­po­l­o­gists at the Uni­vers­ity of Ten­nes­see, Knox­ville. They al­so found that faces have be­come sig­nif­i­cantly nar­rower and higher, though this shift is less pro­nounced than those af­fect­ing the whole cra­ni­um.

An 1847 pho­to of famed Mas­sa­chu­setts sen­a­tor Dan­iel Web­ster (left) and a mod­ern pho­to of pres­i­den­tial can­di­date and form­er Mas­sa­chu­setts gov­er­nor Mitt Rom­ney (right). Their faces may be il­lus­tra­tive of gen­er­al trends af­fect­ing Amer­i­can skulls and faces: they have be­come taller and nar­rower on av­er­age since Web­ster's time, ac­cord­ing to an­thro­pol­o­gist Rich­ard Jantz. The se­lec­tion of these two faces and pho­tos is un­sci­en­tif­ic and they have not been scaled to show their true rel­a­tive sizes.


The changes con­tin­ue in­to the genera­t­ion born in the 1980s, from which come the lat­est skulls avail­a­ble for the re­search, ac­cord­ing to the Jantzes, who pre­sented their find­ings April 14 at the an­nu­al meet­ing in Port­land, Ore. of Amer­i­can As­socia­t­ion of Phys­i­cal An­thro­po­l­o­gists.

“I don’t have any rea­son to be­lieve” the changes have stopped, said Rich­ard Jantz in an in­ter­view.

He cit­ed dra­mat­ic in­creases in the avail­abil­ity of nu­tri­tion, bet­ter med­i­cal care and low­er in­fant mor­tal­ity as pos­si­ble fac­tors be­hind the changes, but ex­pressed pes­si­mism that a de­fin­i­tive rea­son can be iden­ti­fied. The sheer num­ber of changes that have swept Amer­i­can life make that an “end­lessly com­pli­cat­ed” prop­o­si­tion, he said. 

“We are liv­ing in an en­vi­ron­ment that’s to­tally dif­fer­ent from what’s ev­er ex­isted in the past. It’s like put­ting ex­pe­ri­men­tal an­i­mals in an ex­treme en­vi­ron­ment.”

A larg­er head could al­low for great­er in­tel­li­gence, but it’s un­clear wheth­er the in­creases are re­lat­ed to im­prove­ments in in­tel­li­gence scores, Jantz said. Some as­pects of the shifts in skull shape aren’t nec­es­sarily healthy. Ear­li­er pu­ber­ty, which has led to re­ports of girls get­ting preg­nant be­fore their teens, may be re­flected in the ear­li­er clos­ing in youth of a se­par­a­tion in the bone struc­ture of the skull called the sphe­no-occi­pit­al syn­chon­dro­sis, he ob­served. Amer­i­ca’s obes­ity ep­i­dem­ic is the lat­est de­vel­op­ment that could af­fect skele­tal shape, Jantz said, but its pre­cise ef­fects are as yet un­clear. 

Al­though the changes in skull struc­ture may be likely to go on, “they don’t nec­es­sarily have to con­tin­ue in the same di­rec­tion,” he added.

The re­search only ass­essed Amer­i­cans of Eu­ro­pe­an an­ces­try be­cause these pro­vid­ed the larg­est sam­ple sizes to work with, said Jantz. Over 1,500 skulls were in­clud­ed in the re­search, many of them com­ing from the do­nat­ed col­lec­tion at the Uni­vers­ity of Ten­nes­see. 

The av­er­age height from the base to the top of the skull in males has in­creased by 8 mil­lime­ters (0.3 inch­es), the Jantzes found; skull size has grown by 200 cu­bic mil­lime­ters, a space equiv­a­lent to a cou­ple of small peas. In fe­males, the cor­res­pond­ing increases are 7 mil­lime­ters and 180 cu­bic mil­lime­ters.

Changes in skele­tal struc­ture are tak­ing place in many parts of the globe, not just the Un­ited States, Jantz said. But they tend to be less well stud­ied else­where, with the ex­cep­tion of a well-doc­u­ment­ed in­crease in hu­man height across the in­dus­t­ri­al­ized world in re­cent cen­turies. “From what we know, in Eu­rope there are some” shifts in skull shape, Jantz said, but “not as dra­mat­ic as seen in the U.S.” 

Jantz tends to fo­cus on life­style as a prin­ci­ple rea­son for the changes, not hu­man ev­o­lu­tion, al­though he said he does­n’t rule out the lat­ter. The trend in skull shape “tracks calo­ries avail­a­ble pret­ty strong­ly” in the in­dus­t­ri­al­ized world, he not­ed.


The ob­served growth in skull height is to some ex­tent part of an over­all doc­u­mented in­crease in whole-body height. But Jantz has found that the skull-height in­creases are con­sid­er­a­bly out of pro­por­tion to those else­where the body, and al­so have con­tin­ued where­as the over­all height­en­ing has slowed or stopped in re­cent years.

* * *

Send us a comment on this story, or send it to a friend









 

Sign up for
e-newsletter

   
 
subscribe
 
cancel

On Home Page         

LATEST

  • Meet­ing on­line may lead to hap­pier mar­riages

  • Pov­erty re­duction, environ­mental safe­guards go hand in hand: UN re­port

EXCLUSIVES

  • Was black­mail essen­tial for marr­iage to evolve?

  • Plu­to has even cold­er “twin” of sim­ilar size, studies find

  • Could simple an­ger have taught people to coop­erate?

  • Diff­erent cul­tures’ mu­sic matches their spe­ech styles, study finds

MORE NEWS

  • F­rog said to de­scribe its home through song

  • Even r­ats will lend a help­ing paw: study

  • D­rug may undo aging-assoc­iated brain changes in ani­mals

White Americans’ heads and faces have been changing in shape on average, and no one knows quite why, according to new research. In a trend that can be identified going back to the mid-1800s, U.S. skulls have gotten bigger, taller and narrower as seen from the front, said Richard and Lee Jantz, a husband-and-wife team of forensic anthropologists based at the University of Tennessee, Knoxville. They also found that faces have become significantly narrower and higher, though this shift is less pronounced than those affecting the whole cranium. The changes continue into the generation born in the 1980s, from which come the latest skulls available for the research, according to the Jantzes, who presented their findings April 14 at the annual meeting in Portland, Ore. of American Association of Physical Anthropologists. “I don’t have any reason to believe” the changes have stopped, said Richard Jantz in an interview. He cited dramatic increases in the availability of nutrition, better medical care and lower infant mortality as possible factors behind the changes, but expressed pessimism that a definitive reason can be identified. The sheer number of changes that have swept American life make that an “endlessly complicated” proposition, he said. “We are living in an environment that’s totally different from what’s ever existed in the past. It’s like putting experimental animals in an extreme environment.” A larger head could allow for greater intelligence, but whether the increases are related to improvements in intelligence scores is unclear, Jantz said. Some aspects of the shifts in skull shape aren’t necessarily healthy. Earlier puberty, which has led to reports of girls getting pregnant before their teens, may be reflected in the earlier closing in youth of a skull opening called the spheno-occipital synchondrosis, he observed. America’s obesity epidemic is the latest development that could affect skeletal shape, Jantz said, but its precise effects are as yet unclear. Although the changes in skull structure may be likely to go on, “they don’t necessarily have to continue in the same direction,” he added. The research only studied Americans of European ancestry because these provided the largest sample sizes to work with, said Jantz. Over 1,500 skulls were included in the research, many of them coming from the donated collection at the University of Tennessee. The average height from the base to the top of the skull in males has increased by 8 millimeters (0.3 inches), the Jantzes found; skull size has grown by 200 cubic millimeters, a space equivalent to a couple of small peas. In females, the figures are 7 millimeters and 180 cubic millimeters. Changes in skeletal structure are taking place in many parts of the globe, not just the United States, Jantz said. But they tend to be less well studied elsewhere, with the exception of a well-documented increase in human height across the industrialized world in recent centuries. “From what we know, in Europe there are some” shifts in skull shape, Jantz said, but “not as dramatic as seen in the U.S.” Jantz tends to focus on lifestyle as a principle reason for the changes, not human evolution, although he said he doesn’t rule out the latter. The trend in skull shape “tracks calories available pretty strongly” in the industrialized world, he noted.