The homoplastic apes

3 minute read

Bernard Wood and Terry Harrison have published a review paper in NatureWood:Harrison:2011, arguing that the extent of anatomical convergence among Miocene apes makes it difficult to reconstruct their relationships. The keyword of their essay is “homoplasy”, a word for the situation when characters evolve convergently, in parallel, or in reverse. When parallelism or convergence have been common enough, we will find it difficult to use morphological characters to test hypotheses about the phylogeny of species. The butt of their essay is Ardipithecus, with extension to Sahelanthropus and Orrorin:

We emphasize that we are not claiming that the presence of homoplasy in and around the hominin clade, and the other methodological and analytical limitations of phylogenetic analyses noted above, doom all efforts to recover evolutionary relationships to failure. Nor are we claiming that Ar. ramidus, S. tchadensis and O. tugenensis are definitely not hominins. We do, however, advocate that those palaeoanthropologists whose considerable and much valued efforts in the field are rewarded with fossils as significant as those from Aramis, Toros Menalla, Lukeino and Malapa acknowledge the potential shortcomings of their data when it comes to generating hypotheses about relationships.

The main points won’t be news to many readers. One long-time correspondent called the essay “idea homoplasy”, focusing as it does on the same issues that I covered here in 2009, and the evidence for craniodental parallelism among Miocene apes that we reviewed in our 2006 paper on Sahelanthropus sahelanthropus. That’s probably too kind respecting my role in this matter, but I suppose it is one of the chief drawbacks of blogging that I pass by many of these opportunities to do perspective and review articles for top-tier journals. But still, why wait two years to make a point that can really be made in an afternoon, and reach many, many more readers? I mean, Nature wants $32 for this review. Seriously.

I find it nonetheless interesting to see Nature take up the subject, however belatedly, and Wood and Harrison ably cover some of the problems of convergence in Miocene apes. Harrison is an expert on Oreopithecus, and the paper includes four paragraphs describing its relevance to the topic of homoplasy in fossil apes. To me, this is a key comparison that deserves a longer treatment. You can find a bit more information in my 2009 Ardipithecus coverage (“The Ardipithecus pelvis”), but I’m not really the person to do a thorough job of it. I would hope that someone will return to the issue at greater length, but I think that would require access to the Ardipithecus pelvis reconstruction, which is not available for independent inspection.

In light of the Pliocene goat-man lunacy the other day, Daniel Lende ties the satire directly to this little Ardipithecus dustup. He points to the dueling quotes in this Science News article by Bruce Bower:

Researchers have to stop publishing papers that say, essentially, This fossil is an early hominid, so suck it up and accept it, [Bernard] Wood says. Nature and Science could change this practice overnight if they wanted to.
With no new data, no new ideas, no new methods, no new hypothesis, no new experiments, no new fossils, not even a new classification, this paper will leave everybody wondering whats happened to the peer review process at Nature, [Tim] White says.

And then there’s the write-up by Katherine Harmon, who pulls quotes from Nature’s podcast on the paper:

Tim White, of the University of California, Berkeley, and one of the lead authors on the 2009 Ardi papers, called the new article a "six page illustrated op-ed piece" in the Nature podcast. He maintains that "whole functional complexes", not just individual characteristics, that were described in his team's papers link Ardi to humans "to the exclusion of the great apes."

Oh, goodness. I’m not entirely sure what is to be done about these folks. The thing about the 17-year inquiry into the “one large goat” theory, is that I bet they made the CT reconstructions and dental measurements of the goat-men available for inspection.