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Ardi and the human family tree

What the discovery of Ardipithecus ramidus tells us about human evolution—and the link between walking and sex

Move over, “Lucy,” said Larry Dignan in ZDNet. The “fabled” 3.2 million-year-old fossil was “bumped” out of “science’s limelight” Thursday by Ardi—or Ardipithecus ramidus—an earlier human ancestor from Ethiopia’s Afar desert, dating back 4.4 million years. Ardi and her peers represent a middle stage in human evolution, which, surprisingly, was “more modern” than today’s apes and chimpanzees.

That’s important, because for a long time evolutionary biologists thought of chimps as “time machines,” said Joel Achenbach in The Washington Post, or a view into what our common ancestor with apes looked like. But Ardi would be a step back for both humans and chimps, a “sort of hybrid” hominid who mostly lived in trees but also walked upright—“if the scientists are correct,” that is. “Human origins is a field with high stakes and small bones.”

And the bones to this “new alleged missing link” were so fragmented and delicate, said Casey Luskin in the Discovery Institute’s Evolution News & Views, that it took the team of scientists and “reconstructionists” 15 years to put Ardi together. So pardon my “initial reaction of skepticism” to their “Rosetta stone”–level claims.

There’s room for skepticism about whether Ardi was a biped, said Jamie Shreeve in National Geographic, but not about her importance to the field of human evolution. Assuming Ardi did walk on two legs, though, there’s a “provocative theory” as to why: sex. In that scenario, males shifted from fighting each other for mates to a “‘food for sex’ contract” model in which they earned sex by bringing home food—and you need free hands to carry food.

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