American Head Shapes Have Been Changing, But Why?

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.

Adapted from: World Science