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Hominid growth slows to an ape's pace.

Hominid growth slows to an ape's pace

In the past couple of years, the assumption of manypaleoanthropologists that early human ancestors had a prolonged infancy period similar to that of modern humans has been questioned by studies based on two types of tooth analysis. One avenue of this dental work, says B. Holly Smith of the University of Michigan in Ann Arbor, shows that the pattern of tooth eruption in early hominids, or human-like creatures, is more like that of apes than humans.

In an update on a report in NATURE last year, Smith discussedtooth formation in 15 early hominid juvenile jaws compared with dental development in living apes and humans. Two robust australopithecine species, members of a group that split from the human lineage and eventually became extinct, share a unique tooth eruption pattern "that is only superficially human-like,' says Smith. "The pattern resembles neither humans nor apes.' Smith adds that Australopithecus afarensis, thought by many investigators to be the earliest known hominid, has an ape-like eruption sequence, as do A. africanus, Homo habilis and H. erectus, all widely considered to be in the human lineage.

Smith's work, suggesting a relatively short maturation periodin early hominids, is in agreement with a recent study of the timing of early hominid tooth growth by Timothy G. Bromage and C. Christopher Dean of University College in London, England (SN: 10/26/85, p.260). They used an electron scanning microscrope to count ridges on the enamel surface that, according to studies of modern humans and other mammals, form at the rate of about one per week. Australopithecine and early Homo juvenile teeth displayed rapid, ape-like growth.

The two lines of dental evidence suggest, says Smith, thatprolonged care of slowly developing infants and cultural arrangements to deal with this necessity did not emerge until relatively late in human evolution.

The data also indicate, notes Smith, that tooth formation inmodern humans and apes under three years of age "is not nearly as different as we thought it was. Clear differences only emerge at later ages.'
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Title Annotation:research suggests a relatively short maturation period in early hominids
Author:Bower, Bruce
Publication:Science News
Date:Apr 18, 1987
Words:341
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