Who Was Our Last Common Ancestor With Neanderthals?

Written with the assistance of the “New Bing” 

One of the most intriguing questions in human evolution is who was the last common ancestor between modern humans, aka Homo sapiens, and Neanderthals, also known as Homo neanderthalensis. This ancestor would have given rise to two distinct lineages (possibly three when we consider Denisovans, but we are not going to enter that part of the world for this blog post, perhaps a later one!) that coexisted for hundreds of thousands of years and even interbred occasionally. But what did this ancestor look like, when and where did it live, and how do we know?

The answer is not straightforward, as different lines of evidence point to different possibilities. One way to approach this question is to compare the DNA of modern humans and Neanderthals and estimate when they diverged based on the amount of genetic differences. This is a tedious but important process in understanding the relatedness of any two species, at any given time. This method suggests that the last common ancestor lived around 700,000 years ago (National Geographic, 2013). However, this estimate depends on assumptions about the mutation rate and the population size of the ancestral species, which are not well known.

Another way to tackle this question is to look at the fossil record and compare the morphology of different human species. This method is also challenging, as fossils are rare and often incomplete, and morphology can be influenced by factors other than ancestry, such as environment and adaptation. Moreover, different body parts may evolve at different rates, making it hard to assign a fossil to a specific species or lineage. This problem persists throughout all the fossil records, but knowing the distinct morphology of the species you are talking about, can be of huge assistance to assigning fossils to a species. Of course, when we are talking about three species that are so closely related, to the point where they could have interbred, and in fact did, there will be many individuals that share traits from the sister species, muddling the assignment process. Cultural items can, however, also be used to designate species, depending on how the remains were found, i.e. if they were buried or not, and if they were, what materials they were found with. This can not only show the time period in which these remains were laid to rest but also who was responsible. 

One of the most widely accepted candidates for the last common ancestor is Homo heidelbergensis, a species that lived in Africa and Europe between 700,000 and 300,000 years ago. It had a large brain, a robust body, and a mix of primitive and derived features. However, recent studies have cast doubt on this hypothesis. For instance, a study by Gómez-Robles (2019) analyzed the shape of teeth of humans and their relatives and found that Neanderthals and modern humans diverged more than 800,000 years ago, much earlier than previously thought. This would imply that H. heidelbergensis postdates the split and cannot be the common ancestor.

Another possible contender is Homo antecessor, a species that lived in Europe about 1 million years ago. It is known from a few fossils from Spain show some similarities with both Neanderthals and modern humans. A study by Welker et al. (2020) analyzed ancient proteins extracted from one of these fossils and found that H. antecessor was closely related to the last common ancestor of Neanderthals and modern humans. However, this does not necessarily mean that H. antecessor was that ancestor; it could also be a sister group that branched off earlier.

In conclusion, we still do not have a clear picture of who was the last common ancestor between modern humans and Neanderthals. The evidence is fragmentary and conflicting, and more data are needed to resolve this puzzle. However, by combining different sources of information, such as DNA, fossils, and proteins, we can narrow down the possibilities and learn more about our evolutionary history.

References:

Gómez-Robles A (2019) Dental evolutionary rates and its implications for the Neanderthal–modern human divergence. Science Advances 5: eaaw1268.

National Geographic (2013) Much Earlier Split for Neanderthals, Humans? Retrieved from https://www.nationalgeographic.com/culture/article/131021-neanderthal-human-evolution-teeth

Welker F et al. (2020) The dental proteome of Homo antecessor. Nature 580: 235-238.