Not so human after all

Scientists are rethinking a famous fossil often used to illustrate the Darwinian story that humans descended from apes. According to a team of researchers led by Texas A&M paleontologist Thomas Cody Prang, the hands and feet of the ancient extinct species known as Ardipithecus ramidus were more suited to a life swinging in trees than walking upright. Prang’s research into the fossil, known colloquially as Ardi, stands in stark contrast to original reports that hailed it as a candidate for the most recent common ancestor between humans and chimpanzees. The study is the latest to undermine the hopes of Darwinian scientists that they had found evidence of common descent.

Scientists discovered the famous fossil in Ethiopia’s Afar desert area in the 1990s. By 2009, evolutionary scientists announced the skeletal remains belonged to an extinct hominid species that walked upright on two legs—a link between humans and chimpanzees.

But in a Feb. 24 article in the journal Science Advances, Prang argues Ardi’s hands aren’t very human-like. He compared the bones to similar ones in living hominids and found Ardipithecus’ hands were most similar to modern chimpanzee hands, adapted for tree-hanging and knuckle-walking. They bore less resemblance to humans’ general purpose hands. The argument undercuts scientists’ original thesis that Ardi was a common ancestor of apes and humans. The paper follows up on a 2019 study in which Prang questioned Ardi’s bipedalism, arguing in the journal eLife that its feet more closely resembled the grasping feet of chimpanzees or gorillas.

That means Ardi may belong to the chimpanzee family tree, not the human one. “If Ardi looked and walked like a chimp, that should point to it being a chimp-like ancestor of living chimps rather than some kind of an evolutionary ancestor of humans,” said Casey Luskin, the associate director for Discovery Institute’s Center for Science and Culture. “And in fact, that is exactly what this latest evidence shows.”

Some evolutionary scientists are fixated on the search for a last common ancestor between humans and apes. According to the traditional Darwinian theory, hominids like chimpanzees and bonobos, orangutans, gorillas, and humans all branch from the same limb of the tree of life. Known colloquially as the great apes, evolutionary scientists believe the family began to split into more recognizable factions some 14 million years ago.

Ardi isn’t the first supposed connection between humans and apes to be demoted. For scientists, the 1974 discovery of Lucy, a partial skeleton of a hominid, was a bonanza. They quickly declared that Lucy’s extinct species, Australopithecus afarensis, used bipedalism to get around on two feet and hyped it as a proto-human. But more recent research into her skeleton reveals that Australopithecus probably spent much of its time in trees—making it likely just another ape.

“Hominid fossils often go through an arc over their lifetime: They are first hyped in the media as the newest ‘ancestor,’ but then cooler heads prevail and technical, scientific papers are published questioning the hype,” Luskin said. “Ardi follows this pattern.”