The most recent common of Neanderthals and anatomically modern humans has so far proved elusive. A recent study published in the Proceedings of the National Academy of Sciences used quantitative methods to focus on the shape of dental fossils - and found that NO known fossil species is compatible with a recent common ancestor. All late Early and Middle Pleistocene (2.59 million years to 781 to 126 thousand years ago) hominin taxa from Europe were shown to have Neanderthal dental affinities. The researchers also found evidence supporting an early divergence between Neanderthals and modern humans, as early as 1 million years ago. This is 500,000 years earlier than previous estimates.

The study’s authors used approximately 1,200 molars and premolars from 13 species of hominins. They used techniques in morphometric analysis (the structure of their features) and in phylogenetic statistics (the evolutionary relationships between groups of an organism) to reconstruct the dental morphology of the last common ancestor of Neanderthals and modern humans.

None of the hominins which are usually proposed as a common ancestor were found to suit. Often proposed ancestors include Homo heidelbergensis, H. erectus and H. antecessor, but none had a dental morphology fully compatible with the morphology expected of an ancestor of both humans and Neanderthals.

The study also found that the potential human ancestors discovered in Europe have structural features that make them closer to Neanderthals than to modern humans. This evidence suggests that the lineage that led to Neanderthals arose around 1 million years ago, while the divergence of humans took place earlier than thought. Previous studies had placed the divergence between 350,000 and 500,000 years ago.

The authors of this new research also argue that quantitative and statistical methods are a better way of determining human origins than descriptive analyses done in the past. Their methodology may also be used to study other body parts that are represented in the hominin fossil record.

The next step to potentially identifying the common ancestor could come from studying hominin fossils from Africa, though the fossil record from that particular era is meagre. The authors of the study believe that their quantitative approach aids the testing of hypotheses that use the dental fossil record. The same approach could be applied to other skeletal parts using 2D and 3D representations of the morphology of the species.