Recently, paleoanthropologists from the US and Europe sought to identify the common ancestor of modern humans and Neanderthals by reconstructing dental features of this putative species. Comparison of the reconstructed dental anatomy with that of known hominids failed to find a match. Based on this study, it looks as if the most reasonable candidates (H. erectus, H. antecessor, and H. heidelbergensis) for the common ancestor of modern humans and Neanderthals are no longer in contention. The inability of paleoanthropologists to pinpoint this key evolutionary ancestor doesn’t bode well for the idea of human evolution.
Many scientists think that humans evolved and share an ancestor with chimpanzees and bonobos. To justify this view, they point to the hominid fossil record. Paleoanthropologists have unearthed a number of hominid species from sites in Africa, Asia, the Middle East, and Europe. These creatures first appeared in the fossil record about 7 million years ago and persisted until just a few thousand years ago.
Paleoanthropologists interpret the hominids as intermediate forms that document the evolutionary transformations that produced modern humans. Some of these creatures are thought to be evolutionary side branches rather than candidates for the direct evolutionary ancestors to modern humans. Yet, for those that may well be part of our direct evolutionary lineage, scientists still don’t understand how these species relate to each other and modern humans.
For an introductory discussion of the struggles paleoanthropologists experience in interpreting the hominid fossil record and for a summary of RTB’s views on human evolution and the hominids check out this video.
Recent research by a team of collaborators from the US and Europe highlights the problem paleoanthropologists have interpreting the fossil record.1 These researchers were trying to identify the common hominid ancestor shared (labeled MH-N LCA) by modern humans and Neanderthals. Relying on genetic comparisons, paleoanthropologists think that modern humans and Neanderthals shared an ancestor about 800,000 years ago. (Once these two lineages diverged, the one leading to Neanderthals split again around 650,000 years ago producing Neanderthals and the mysterious Denisovans.) The prime candidates for the MH-N LCA are either Homo heidelbergensis or Homo antecessor. (Though some data suggests that H. antecessor is just an evolutionary side branch.)
The strategy these researchers took to identify the MH-N LCA focused on comparative analysis of hominid teeth. This was no small feat. They examined 1,200 fossil teeth, representing 12 hominid species. Using newly developed analytical techniques, the investigators reconstructed the dental anatomy of the putative MH-N LCA. They hoped to match the reconstructed dental features with those of the candidate species.
Unfortunately, the reconstructions didn’t match the dental characteristics of any known hominid fossil. In other words, the dental features of MH-N LCA didn’t match those of H. heidelbergensis, H. antecessor, or H. erectus—a disappointing and unexpected result.
Based on their analysis, the researchers also concluded that MH-N LCA must have lived over 1 million years ago, much earlier than the genetic data indicates. Aida Gómez-Robles, the lead author of the study, bemoaned, “Our results call attention to the strong discrepancies between molecular and paleontological estimates of the divergence time between Neanderthals and modern humans. These discrepancies cannot simply be ignored, but have to be somehow reconciled.”2
The researchers have attempted to account for their null result by speculating that dental anatomy may not be useful for ancestral reconstructions. Other researchers have demonstrated that dental data can’t be used to build reliable evolutionary trees. If so, then this approach may be flawed fundamentally. The team also suggests that they may not have been looking in the right location. They limited their analysis to fossil remains recovered in Europe; so they also suggest that maybe H. heidelbergensis specimens from Africa might fit the bill instead. Still, there is no reason to think that the European and African forms of H. heidelbergensis would be that different.
Clearly, there is more work to be done. It is interesting that when researchers attempted to identify the common ancestor that gave rise or modern humans and Neanderthals, they were unable to do so. This does not bode well for the idea of human evolution.
1. Aida Gómez-Robles et al., “No Known Hominin Species Matches the Expected Dental Morphology of the Last Common Ancestor of Neanderthals and Modern Humans,” Proceedings of the National Academy of Sciences, USA (published electronically October 21, 2013): doi: 10.1073/pnas.1302653110.
2. Indiana University, “No Known Hominin is Common Ancestor of Neanderthals and Modern Humans, Study Suggests,” ScienceDaily, posted October 21, 2013, http://www.sciencedaily.com/releases/2013/10/131021153202.htm.