Evolution's Bad Girl: Ardi Shakes Up the Fossil Record

Bower, Bruce, Science News

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She's the ultimate evolutionary party crasher. Dubbed Ardi, her partial skeleton was unearthed in Ethiopia near the scattered remains of at least 36 of her comrades. Physical anthropologists had known about the discovery of this long-gone gal for around 15 years, but few expected to see the 4.4-million-year-old hell-raiser that was unveiled in 11 scientific papers in October.

Like a biker chick strutting into a debutante ball, Ardi brazenly flaunts her nonconformity among more-demure members of the human evolutionary family, known as hominids. She boasts a weird pastiche of anatomical adornments, even without tattoos or nose studs. In her prime, she moved slowly, a cool customer whether upright or on all fours. Today, she's the standard bearer for her ancient species, Ardipithecus ramidus.

And in true biker-chick fashion, Ardi chews up and spits out conventional thinking about hominid origins, according to a team--led by anthropologist Tim White of the University of California, Berkeley--that unearthed and analyzed her fragile bones (SN: 10/24/09, p. 9). First, White and his colleagues assert, Ardi's unusual mix of apelike and monkeylike traits demolishes the long-standing assumption that today's chimpanzees provide a reasonable model of either early hominids or the last common ancestor of people and chimps--an ancestor which some scientists suspect could even have been Ardi, if genetics-based estimates of when the split occurred are borne out.

Second, the team concludes, Ardi trashes the idea that knuckle-walking or tree-hanging human ancestors evolved an upright gait to help them motor across wide ancient savannas. Her kind lived in wooded areas and split time between lumbering around on two legs hominid-style and cruising carefully along tree branches on grasping feet and the palms of the hands.

One member of White's team argues for a controversial possibility: that two-legged walking evolved because Ardipithecus males had small canine teeth. Many living and fossil male apes fight for mates by wielding formidable canines, but Ardi's male counterparts had to band together and forage over long distances to obtain mates, his thinking goes.

In a third slap at scientific convention, Ardi fits a scenario in which a few closely related hominid lineages preceded the larger-brained Homo genus that emerged around 2.4 million years ago, White says. In contrast, many anthropologists think of hominid evolution …

Questia, a part of Gale, Cengage Learning. www.questia.com
Publication information: Article title: Evolution's Bad Girl: Ardi Shakes Up the Fossil Record. Contributors: Bower, Bruce - Author. Magazine title: Science News. Volume: 177. Issue: 2 Publication date: January 16, 2010. Page number: 22+. © 2009 Science Service, Inc. COPYRIGHT 2010 Gale Group.

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