Paleoanthropologists Disown <i>Homo habilis</i> from Our Direct Family Tree - Evolution News & Views

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Paleoanthropologists Disown Homo habilis from Our Direct Family Tree

An Associated Press article titled "African fossils paint messy picture of human evolution" explains that common popular conceptions of human evolution are incorrect: "Surprising fossils dug up in Africa are creating messy kinks in the iconic straight line of human evolution with its knuckle-dragging ape and briefcase-carrying man." Indeed, the inappropriateness of such "straight line" depictions of human evolution was one of Jonathan Wells' main points in chapter 11 in Icons of Evolution, "From Ape to Human: The Ultimate Icon." A Harvard biological anthropologist stated the newly reported fossils reveal, "how poorly we understand the transition from being something much more apelike to something more humanlike." The Associated Press article goes on to explain why Homo habilis can no longer considered a direct ancestor of humans:

The old theory was that the first and oldest species in our family tree, Homo habilis, evolved into Homo erectus, which then became us, Homo sapiens. But those two earlier species lived side-by-side about 1.5 million years ago in parts of Kenya for at least half a million years, Leakey and colleagues report in a paper published in Thursday's journal Nature. In 2000 Leakey found an old H. erectus complete skull within walking distance of an upper jaw of the H. habilis, and both dated from the same general time period. That makes it unlikely that H. erectus evolved from H. habilis, researchers said.
In other words, habilis can no longer be considered the ancestor to the rest of the genus Homo.

Indeed, this has been a growing trend in paleoanthropology. A 1999 paper published in Science by two leaders in the field explained that "Homo" habilis should not even be considered a member of Homo, but is rather an australopithecine due to its ape-like skeletal structure (see B. Wood & M. Collard, "The Human Genus," Science, Vol. 284:65-71, April 2, 1999). The table showing the australopithecine ape-like skeletal characteristics of habilis from Wood & Collard's paper is reproduced below:

table1_wood-collard-recreation.jpg

With habilis removed from our direct ancestry, what exactly is the direct ancestor of Homo? As two paleoanthropologists wrote in Nature, researchers don't know:

[Early forms of erectus] mar[k] such a radical departure from previous forms of Homo (such as H. habilis) in its height, reduced sexual dimorphism, long limbs and modern body proportions that it is hard at present to identify its immediate ancestry in east Africa. Not for nothing has it been described as a hominin "without an ancestor, without a clear past"

(Robin Dennell & Wil Roebroeks, "An Asian perspective on early human dispersal from Africa," Nature, Vol 438:1099-1104 (Dec. 22/29, 2005) (internal citations removed) (emphasis added).)

After this latest find, one researcher realized its implications and was quick to quash any doubts this may spark regarding human evolution, stating: "All the changes to human evolutionary thought should not be considered a weakness in the theory of evolution, Kimbel said. Rather, those are the predictable results of getting more evidence, asking smarter questions and forming better theories, he said."

I'm all for "asking smarter questions and forming better theories," and it logically follows that I therefore must also favor abandoning theories that aren't working. The aforementioned Harvard biological anthropologist, Daniel Lieberman, apparently did not get the memo about refraining from making statements that might lead to doubts about evolution: he stated in the New York Times that these latest fossil finds regarding habilis:

"show 'just how interesting and complex the human genus was and how poorly we understand the transition from being something much more apelike to something more humanlike.'" (emphasis added)
Indeed, as explained here, the first true members of Homo were "significantly and dramatically different" from our alleged ape-like ancestors, the australopithecines. So far, the data isn't doing a very good job of explaining precisely from what, if anything, did our genus Homo evolve.