TREES CAST A SHADOW OVER SOME CLAIMS: CASE STUDIES FROM FOSSIL HOMININ PHYLOGENETICS (Invited Presentation)

The hominin fossil record currently suggests that there may be as many as 29 species of hominins that have existed in the last seven million years. However, there is little consensus among paleoanthropologists on the validity of some of these species, and many questions remain about the evolutionary relationships of others. Given that a reliable phylogeny is necessary in the study of human evolution, it is important to explore the phylogenetic uncertainties of fossil hominins.

In the last 20 years, likelihood-based phylogenetic techniques, such as maximum likelihood and Bayesian inference, have become more popular among biologists. However, for various complex reasons, the application of these systematic methods has been slow to permeate into the discipline of paleoanthropology. The adoption of these systematic methods is advantageous for a couple of reasons. First, unlike the maximum parsimony analysis that has been popular in this discipline, Bayesian approaches allow us to not only generate phylogenetic trees, but also to formally evaluate relative support for competing hypotheses of phylogenetic relationships. Second, we can incorporate geological data associated with the fossils directly to simultaneously infer the tree topology and to date the tree by calibrating the morphological clock. We have taken advantage of these methodological features of the Bayesian approach to evaluate the evolutionary relationships of problematic fossil hominins species.

Here, we discuss two case studies in which we explored phylogenetic questions related to two recently discovered hominin species, Homo floresiensis and H. naledi using tip-dated Bayesian phylogenetic inference. There has been a lot of controversy on the validity and the phylogenetic positions of H. floresiensis and H. naledi since their discoveries. We tested various evolutionary hypotheses on H. floresiensis using Bayes factors, and we explored the phylogenetic position of H. naledi and estimated its age using a calibrated morphological clock in a dated Bayesian phylogenetic analysis. These findings strongly suggest that the use of Bayesian phylogenetic methods is very promising for paleoanthropology. This phylogenetic approach allows paleoanthropologists to systematically test the strength of support for certain hypotheses and move the debate forward to improve our understanding of hominin evolution.