For many years, Discovery Institute spokesperson Casey Luskin has been telling the world that the genus Homo is preceded by no transitional forms, because the species typically thought to be transitional between australopithecines and Homo, Homo habilis, is actually an Australopithechus itself. Poof, there goes the transition. As I pointed out long ago, this argument about what names to apply to fossils under Linnaean taxonomy is basically pointless – the fossils stay transitional in time and in morphology no matter what names you give them – but creationists like Luskin don’t care about that (and don’t give me that silliness about ID advocates not being creationists, Luskin is arguing for the special creation of humans, for goodness’ sake!).* Instead, they love to misrepresent the terminological dispute to obscure the actual big picture of the data.
Unfortunately for Luskin, though, other creationists play the same game, and, don’t you know it, it turns out that the transitional specimens come out as transitional in their latest analysis. Bryan College creationist Todd Wood is announcing his “baraminological”** analysis of Homo habilis, Australopithecus sediba, and other fossils. He took a bunch of cladistic datasets from the paleoanthropology literature (all based on crandiodental characters) and put them through his “baraminological distance” algorithm to see where there are clusters and gaps. He concludes that the recently-discovered Australopithecus sediba should actually be Homo sediba, but this is just this is what several paleoanthropologists said after it was published. More significantly for our interests, instead of saying that habilis is just another ape far removed from Homo, Wood concludes that habilis clearly groups with the rest of Homo, and that big, unfillable, magical God-obviously-acted-here gap, which all creationists mindlessly, dogmatically believe in come hell or high water, is actually between habilis and the australopiths. Whoops!
Here’s some quotes:
“These rapid, unique, and genetically significant changes are termed “a genetic revolution” where “no australopithecine species is obviously transitional.” One commentator proposed this evidence implies a “big bang theory” of human evolution. Now that “Homo” habilis is best recognized as an australopithecine due to its ape-like skeletal structure (see “The Human Genus,” Science, 284:65-71), it is no wonder an article in Nature last year recognized the lack of a clear-cut immediate ancestor for our genus Homo…”
“In other words, habilis can no longer be considered the ancestor to the rest of the genus Homo.”
But the exhibit gives no evidence of dissent from the official party line, such as an admission from Ernst Mayr in 2004 that “[t]he earliest fossils of Homo, Homo rudolfensis and Homo erectus, are separated from Australopithecus [sic, should be italicized] by a large, unbridged gap,” and therefore we’re in a position of “[n]ot having any fossils that can serve as missing links.”
I guess according to the Smithsonian’s exhibit, this large, unbridged gap is just more evidence for evolution.
Most surprising, three controversial taxa appear to be unequivocally grouped with the homininans: Homo habilis, Homo rudolfensis, and Australopithecus sediba. As noted above, Hartwig-Scherer (1999) considers H. habilis an australopith, but Lubenow (2004, pp. 299-301) and Line (2005a) believe some H. habilis specimens might be human. Additional creationists who reject the human status of H. habilis include Gish (1995, p. 279), Hummer (1979), Mehlert (1996), Murdock (2006), and Young (2006). Likewise, though Lubenow (2004, pp. 328-329) and Cuozzo (1977) believe H. rudolfensis to be human, Hartwig-Scherer and Brandt (2007) consider it a kind of ape. As of this writing, there has been no creationist commentary or interpretation of Au. sediba, but given sediba‘s extremely ape-like forearms (Berger et al. 2010), it seems likely that many creationists would prefer to place sediba among the australopiths.
So there you have it. Wood has “saved” the distinctiveness of humans, but only by including habilis and sediba, which some paleoanthropologists (and even more creationists) thought were so different from humans that they should be in a whole different genus, and which had brains much closer to the size of chimp brains than to modern human brains. Wood continues by looking for the silver lining:
Despite these contradictory opinions, the present results strongly support the classification of all three species in the human holobaramin. All analyses showed all three taxa clearly clustering with other homininans and separately from other australopiths.
Well, except for Australopithecus africanus, which just happens to be the australopithecine that is the closest relative of Homo…
The position of Au. africanus is somewhat less clear. In the BDC analysis of the datasets of Strait and Grine (2001; 2004) and Smith and Grine (2008), Au. africanus was positively correlated with one and four homininans respectively. In both cases, Au. africanus appeared as an outlier from the Homo cluster in 3D MDS. In the case of Strait and Grine’s 2001 dataset, the positive correlation between Au. africanus and H. rudolfensis had bootstrap support of only 62%, indicating that the positive correlation was especially sensitive to changes in the character states used to calculate baraminic distances. Likewise, the bootstrap support for the africanus/rudolfensis correlation in Strait and Grine’s 2004 dataset was 59%. In the case of Smith and Grine’s (2008) dataset, reduction of the number of outgroup taxa eliminated all positive correlation between Au. africanus and homininans. In BDC analysis of the Strait, Grine, and Moniz (1997) and Berger et al. (2010) datasets, no positive or negative correlation was observed between Au. africanus and homininans. Zeitoun’s (2000) dataset showed significant, negative BDC between the Au. africanus specimen Sterkfontein 5 and most of the homininan specimens. In summary, the evidence for including Au. africanus within the human holobaramin appears quite weak.
However, Wood neglects to point out that afarensis doesn’t form a (phenetic, remember) cluster with the apes or other australopithecines, either. In some of his MDS (multi-dimensional scaling, a way of representing distances between a bunch of points where each point has measurements in many dimensions) plots, afarensis comes out pretty much exactly between Homo and non-Homo.
this present study should end charges against creationists that classification of australopiths or “early Homo” as human or ape is arbitrary and meaningless (for example, Conrad 1986-1987; Kitcher 1983, p. 154; Miller 2008, p. 93; Nickels 1986-1987). Rather than looking at a handful of traits or casually declaring australopiths to be apes, the present study has supported the separate classification of humans (genus Homo sensu lato) and as many as three groups containing australopith taxa, based on a suite of characters selected from conventional paleoanthropology studies.
Unfortunately, it still remains the case that creationist classifications of hominins are arbitrary and meaningless. The first principle of baraminology is that the Bible is always right, and if the rest of the data contradicts the Bible, then so much the worse for the data. So Wood, whatever spark he may sometimes show amongst the pitiful intellectual trainwreck that is creationism, has already committed intellectual suicide on this issue and guaranteed that the data could never change his mind on the key question he is allegedly assessing, the special creation of humans. Even if he did decide to give the data the final word, his analysis consists of drawing circles around phenetic clusters, with no principles about how to decide when things are in the same cluster or not (such methods do commonly exist in statistics, but they would create the danger of getting an answer one doesn’t like).
And finally, it’s pretty clear that people like Luskin and the Discovery Institute aren’t going to change their mind on this one. Unless you are prepared to take the Todd Wood/Kurt Wise position and simply assert that the literal interpretation of the Bible comes first and the data fundamentally don’t matter, if you’re a creationist and you admit that Homo habilis shares common ancestry with Homo sapiens, it’s all over but the whining.
* Actually understanding these naming and classification issues in paleoanthropology involves delving into the history of systematics and cladistics in evolutionary biology generally and in paleoanthropology specifically. Each time Luskin quotes someone, you have to ask if the writer in question is a fan of Mayrian “evolutionary systematics”, where you lump specimens into species and genera based on overall similiarity and some kind of gestalt sense of what a “genus” is. Or are they adhering to cladistic principles of “phylogenetic systematics”, where only shared derived characters are considered informative? Does the writer think taxa should be monophyletic, or is polyphyly ok? Are they defending some taxonomic scheme for reasons of convenience, or as an approximate description of the morphology, or to buttress some hypothesized set of ancestor-descendent relationships, or to propose an explicit, cladistically testable phylogeny? Is the writer Ernst Mayr, arch-defender of “evolutionary systematics”, writing at the age of 99 on a topic well outside his speciality? [also, Mayr says in a footnote that Luskin leaves out of his quote, “I follow those who place Homo habilis in the genus Australopithecus”] Or is the writer some marginally-informed journalist who couldn’t tell you the difference between “evolutionary systematics” and “phylogenetic systematics”, the difference between Linnaean taxonomy and rank-free taxonomy, the difference between characters that are shared with outgroups (and thus don’t give any grouping information about the ingroup) and characters that are only shared by a subset of taxa in the ingroup (and thus give grouping information), or the difference between classifications that allow polyphyly and those that don’t, and therefore sprinkles their article with vague comments about “big differences” and “small differences” and “ancestral”/”not ancestral”, without any sense of the (very narrow!) scale of the actual differences between these positions when applied to a bunch of closely-related hominin fossils?
** “Barminology” is the creationist study of “bara mins” (“created kinds” in Hebrew). The key metric, “baraminic distance” basically seems to be a phenetic clustering method, where groupings are done by eye and outgroups are excluded if they make the ingroups seem too similar.