Another Fossil Human Ancestor Claimed
Meet Australopithecus sediba – or is it Homo something? Scientists are arguing over how to classify new fossils found in a cave at Malapa, South Africa. Announced today in Science,1 the fossils, alleged to be just under 2 million years old, are producing a strange mixture of hopeful headlines and cautionary counsels from experts.
As could be expected, headlines in the popular press tease their readers with tantalizing titillations: “Fossil Skeletons May Be Human Ancestor” wrote Charles Q. Choi for Live Science. Ker Than wrote “‘Key’ Human Ancestor Found: Fossils Link Apes, First Humans?” for National Geographic. And Jeff Hecht wrote “Almost human: closest australopithicine [sic] primate found” for New Scientist. And anything that might please Darwin has to include the shedding-light motif: Science Daily’s long headline proclaimed, “New Hominid Shares Traits With Homo Species: Fossil Find Sheds Light on the Transition to Homo Genus from Earlier Hominids.” True to tradition, PhysOrg dutifully paraded the iconic image of the march of progress from ape to man, complete with racist skin colors and sexist depictions of naked males only, their right legs or arms artfully concealing their private parts. It’s not quite clear why most of these charts leave the highest man beardless, unless the chart is Lamarckian, in which case a spare tire should also be evident.
Yet a closer look at the articles reveals a great deal of doubt about many aspects of the story.
- Taxonomy: Experts disagreed strongly on whether these specimens should be classified within Australopithecus or Homo. If it had been classified within Homo, it would have represented a dead-end lineage of no consequence to human evolution. There appears to have been a strong controversy between the discoverers and other experts about which taxon to use.
- Traits: The skeletons appear to have a mosaic of traits: long limbs and small brain capacity, but indications of upright posture and human-like teeth.
- Provenance: Experts disagreed whether the bones were buried together, or fell through to other levels after burial.
- Dating: The dating depends on the provenance, yet was measured with U-Pb dating of materials below the bones. Assigning a date is critical to how evolutionists perceive the specimen’s relationship to human ancestry.
- Hope: No one is claiming these fossils clarify a human evolution story. Hopes that it might are put in future tense: “This new Australopithecus sediba species might eventually clear up that debate, and help to reveal our direct human ancestors.”
- Credibility: Lee Berger, the lead author of the paper, has been involved in sharp controversies with other paleoanthropologists about which hominids represent human ancestors. Michael Balter wrote for Science,2 “Some of Berger’s other past claims have sparked strong criticism, including a highly publicized 2008 report of small-bodied humans on Palau, which Berger thought might shed light on the tiny hobbits of Indonesia. But other researchers say the Palau bones belong to a normal-sized modern human population.” Berger gave this new fossil a suggestive name: sediba is local lingo for “wellspring” – as if his discovery can garner significance merely by naming it that way.
- Candidacy: Michael Balter’s headline in Science accompanying the paper is more guarded than the popular press: “Candidate Human Ancestor From South Africa Sparks Praise and Debate.”
- Dispute: Balter quoted Tim White’s opinion: “Given its late age and Australopithecus-grade anatomy, it contributes little to the understanding of the origin of genus Homo.”
- Burial: The authors’ hypothesis about how the bones were buried contains many ad-hoc elements (see below).
- Sequence: Balter considered the opinion of Chris Stringer of the London Natural History Museum: in summary, “At no earlier than 2 million years old, A. sediba is younger than Homo-looking fossils elsewhere in Africa, such as an upper jaw from Ethiopia and a lower jaw from Malawi, both dated to about 2.3 million years ago.”
- Deflation: Even Lee Berger, the discoverer, made this admission: “Berger and his co-workers agree that the Malapa fossils themselves cannot be Homo ancestors but suggest that A. sediba could have arisen somewhat earlier, with the Malapa hominins being late-surviving members of the species.”
- Meaning: All Balter could say in conclusion is confusion: “However they are classified, the Malapa finds ’are important specimens in the conversation’ about the origins of our genus, says [Susan] Ant�n [New York U], and ‘will have to be considered in the solution.’” The statement implies that the conversations do not include solutions – only questions.
A second paper accompanying the discovery announcement considered the geological context of the fossils.3 It defends a hypothesis that the skeletons were buried in a debris flow into the cave before scavengers could harm them. Others, however, are not so sure: “Geochemist Henry Schwarcz of McMaster University in Hamilton, Canada, notes that the team suggests that the hominin bodies might have been moved by river flows after they fell into the cave from holes in the earth above,” explained Michael Balter. “If so, the fossils may not be tightly associated with the dated deposits below and above them.” Dirks et al dispute that, calling attention to the fact that “the bones were partly articulated with each other, implying that they were buried soon after death.” A lot of interpretation depends, however, on the dating of the sediments above and below the bones. The paper’s hypothesis includes many ad-hoc elements: carnivores were attracted to vertical shafts where prey animals had fallen to their deaths: “These factors could have operated to accumulate a diverse assemblage of carcasses in the chamber below, away from carnivore activity,” the authors speculated. “The sediments imply that subsequent high-volume water inflow, perhaps the result of a large storm, caused a debris flow that carried the still partially articulated bodies deeper into the cave, to deposit them along a subterranean stream.” It would seem this complex sequence of happenstance occurrences would obfuscate any conclusions about dating.
Update 04/09/2010: True to tradition, the counter-claims quickly ensued. “Please, please, not again,” moaned Carl Zimmer in Slate, recalling the hype about Ida last year (05/19/2009, 03/03/2010). Zimmer accepts evolution but denies (with Berger) that the term “missing link” have any validity. As for this fossil, “None of the experts I spoke to this week were ready to accept Berger’s hypothesis about A. sediba’s special place in the hominin tree,” he said. “It might actually belong to a different branch of hominin evolution. It may have evolved its Homo-like traits independently of our own ancestors.” It would seem its ability to illuminate much of anything about human history is dubious. Zimmer quoted Daniel Lieberman of Harvard admitting, “The origins of the genus Homo remain as murky as ever.”
Meanwhile, Nature News weighed in on the significance (or lack of it) of this fossil. “Claim over ‘human ancestor’ sparks furore,” headlined Michael Cherry: “the researchers’ suggestion that the fossils represent a transitional species in human evolution, sitting between Australopithecus and Homo species, has been criticized by other researchers as overstated.” Quotes from Tim White (UC Berkeley) were especially harsh. He said the Berger team’s claim that these skeletons had anything to do with the rise of Homo is “fossil-free speculation” adding with Ida overtones, “the obsession with Homo in their title and text is difficult to understand outside of a media context.” Another said the bones could represent nothing more than variation within other known species. Another noted that the earliest Homo skeleton predates this find by half a million years. Berger countered that the earlier fossils are less complete. A supporter of Berger’s classification may have taken more than he gave when he said, “The Malapa specimens will rekindle the debate about the validity of the taxon Homo habilis, and will make us look more carefully at the variability of Australopithecus africanus and her sister species.” (For info on Homo habilis, see 08/09/2007, 05/27/2009, and 09/21/2009). Cherry ended his article with doubt: “the latest finds raise important questions about the ancestry of humans.” That statement raises the possibility that Berger’s fossil is a step backwards in understanding. For difficulties with the Homo classification, see the 05/27/2009 entry.
1. Berger et al, “Australopithecus sediba: A New Species of Homo-Like Australopith from South Africa,” Science, 9 April 2010: Vol. 328. no. 5975, pp. 195-204, DOI: 10.1126/science.1184944.
2. Michael Balter, “Candidate Human Ancestor From South Africa Sparks Praise and Debate,” Science, 9 April 2010: Vol. 328. no. 5975, pp. 154-155, DOI: 10.1126/science.328.5975.154.
3. Dirks et al, “Geological Setting and Age of Australopithecus sediba from Southern Africa,” Science, 9 April 2010: Vol. 328. no. 5975, pp. 205-208, DOI: 10.1126/science.1184950.
If the storytellers cannot agree on their own story, why should the audience judge the performance a history class rather than a comedy? The bones are real; the interpretations are highly questionable and fallible. Most likely this is another extinct ape out of many extinct apes that lived not so long ago. Wishful-thinking Darwinian paleoanthropologists are eager to divine human attributes in whatever bones they find. They fight and squabble over where the bones fit into their mental picture of how philosophers emerged from screeching monkeys in the trees. Pay them no mind; we’ve seen this comedy show so many times before, and we know the eventual outcome. Someone else will appear on stage with a new bone and announce, “Everything you know is wrong.” (02/23/2001, 02/19/2004).