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If Humans Were Built to Last

By S. Jay Olshansky, Bruce A. Carnes and Robert N. Butler

We would look a lot different—inside and out—if evolution had designed the human body to function smoothly not only in youth but for a century or more.

Coverpainting by Kazuhiko Sano. This depiction of Sahelanthropustchadensis— potentially the oldest hominid yet found—is based on cranial and dental remains.

Scientific American Special (ISSN 1048-0943], Volume 13, Number 2,2003, published by Scientific American, Inc., 415 Madison Avenue, New York, NY 1001?-1111. Copyright © 2003 by Scientific American, Inc. All rights reserved. No part of this Issue may be reproduced by any mechanical, photographic or electronic process, or In the form of a phonographic recording, nor may It be stored in a retrieval system, transmitted orotherwlse copied for public or private use without written permisslonofthe publisher. Canadian BN No. 12?38?652RT; OST No. 0101533253?. To purchase additional quantities: U.S., $10.95 each; elsewhere, $13.95 each. Send payment to Scientific American, Dept. EV0L, 415 Madison Avenue, New York, NY 1001?-1111. Inquiries: fax 212-355-0408 or telephone 212451-8890. Printed in U.S.A.

An CESTÖR

Controversial new fossils could bring scientists closer than ever to the origin of humanity to Call Our Own

By Kate Wong

POITIERS, FRANCE—Michel Brunet removes the cracked, brown skull from its padlocked, foam-lined metal carrying case and carefully places it on the desk in front of me. It is about the size of a coconut, with a slight snout and a thick brow visoring its stony sockets. To my inexpert eye, the face is at once foreign and inscrutably familiar. To Brunet, a paleontologist at the University of Poitiers, it is the visage of the lost relative he has sought for 26 years. "He is the oldest one," the veteran fossil hunter murmurs, "the oldest hominid."

Brunet and his team set the field of paleoanthropology abuzz when they unveiled their find in July 2002. Unearthed from sandstorm-scoured deposits in northern Chad's Djurab Desert, the astonishingly complete cranium—dubbed Sahelanthropus tchadensis (and nicknamed Toumai, which means "hope of life" in the local Goran lan-guage)—dates to nearly seven million years ago. It may thus represent the earliest human forebear on record, one who Brunet says "could touch with his finger" the point at which our lineage and the one leading to our closest living relative, the chimpanzee, diverged.

APE OR ANCESTOR? Sahelanthropus tchadensis, potentially the oldest hominid on record, forages in a woodland bordering Lake Chad some seven million years ago. Thus far the creature is known only from cranial and dental remains, so its body in this artist's depiction is entirely conjectural.

Less than a century ago simian human precursors from Africa existed only in the minds of an enlightened few. Charles Darwin predicted in 1871 that the earliest ancestors of humans would be found in Africa, where our chimpanzee and gorilla cousins live today. But evidence to support that idea didn't come until more than 50 years later, when anatomist Raymond Dart of the University of the Witwatersrand described a fossil skull from Taung, South Africa, as belonging to an extinct human he called Australopithecus africanus, the "southern ape from Africa." His claim met variously with frosty skepticism and outright rejection—the remains were those of a juvenile gorilla, critics countered. The discovery of another South African specimen, now recognized as A. robustus, eventually vindicated Dart, but it wasn't until the 1950s that the notion of ancient, apelike human ancestors from Africa gained widespread acceptance.

In the decades that followed, pioneering efforts in East Africa headed by members of the Leakey family, among others, turned up additional fossils. By the late 1970s the austra-lopithecine cast of characters had grown to include A. boisei, A. aethiopicus and A. afarensis (Lucy and her kind, who lived between 2.9 million and 3.6 million years ago during the Pliocene epoch and gave rise to our own genus, Homo). Each was adapted to its own environmental niche, but all were bipedal creatures with thick jaws, large molars and small ca-nines—radically different from the generalized, quadrupedal Miocene apes known from farther back on the family tree. To probe human origins beyond A. afarensis, however, was to fall into a gaping hole in the fossil record between 3.6 million and 12 million years ago. Who, researchers wondered, were Lucy's forebears?

Despite widespread searching, diagnostic fossils of the right age to answer that question eluded workers for nearly two decades. Their luck finally began to change around the mid-1990s, when a team led by Meave Leakey of the National Museums of Kenya announced its discovery of A. anamensis, a four-million-year-old species that, with its slightly more archaic characteristics, made a reasonable ancestor for Lucy [see "Early Hominid Fossils from Africa," on page 14]. At around the

Overview/The Oldest Hominids i The typical textbook account of human evolution holds that humans arose from a chimpanzeelike ancestor between roughly five million and six million years ago in East Africa and became bipedal on the savanna. But until recently, hominid fossils more than 4.4 million years old were virtually unknown.

i Newly discovered fossils from Chad, Kenya and Ethiopia may extend the human record back to seven million years ago, revealing the earliest hominids yet. i These finds cast doubt on conventional paleoanthro-pological wisdom. But experts disagree over how these creatures are related to humans—if they are related at all.

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