Sophie Teall writes about how the discovery of an archaic human population in Israel suggests a more complex evolutionary history than previously thought.
As modern humans (Homo sapiens), we are the only members of the group Homo still walking the earth. It is easy to forget that several human lineages have called this planet home. Perhaps the most famous are Neanderthals (Homo neanderthalensis), who lived in Eurasia until around 40,000 years ago. However, piecing together our evolutionary history from scattered fossil clues is far from easy.
A new piece to this vast puzzle has been discovered near Nesher Ramla, Israel. Amongst stone tools and animal bones, a team led by archaeologist Yossi Zaidner from the Hebrew University of Jerusalem excavated 17 bone fragments from an individual living 130,000 years ago. At Tel Aviv University, manual and virtual alignments revealed that the fragments formed parts of the braincase and an almost complete lower jaw, including a tooth.
Homo sapiens began to live in the region 200,000 years ago, so researchers expected the individual to be an early Homo sapien. However, the analysis revealed this was not the case. This individual had the unique Homo sapien feature of a chin while the skull had different traits. Our braincase is tall and rounded, but this individual had a low and flat skull formed from a thicker layer of bone. Additionally, the patterning of the arterial branches supplying blood to the brain was less complex than seen in Homo sapiens. It is important to remember that this difference does not indicate brain size or intelligence. Studies have found that other archaic humans produced the same technologies as Homo sapiens, including fire maintenance and the cooking of meat.
Having determined that the fragments did not belong to an early Homo sapien, they were then compared to other groups. The individual had the most similarity to fossils previously found in Israel, once believed to be archaic Homo sapiens. It has since been recognised that they formed part of a large population of different human lineages in the area, between 400,000 – 130,000 years ago, spending part of that time co-existing with Homo sapiens.
Since the fragments found at Nesher Ramla likely belonged to an individual in this population, the team could not classify them as a new species. Instead, the individual is classified as a part of the Nesher Ramla Homo population. Despite being the smallest unit for grouping organisms, defining a species is messy and complicated with no single definition suitable for all organisms. Living organisms are grouped via properties such as appearance, role in the ecosystem or ability to produce fertile offspring. Yet the waters become muddier for extinct organisms where many traits are no longer observable. Additionally, the presence of hybridisation, or gene flow between two species, challenges the idea that species are genetically isolated.
Throughout human evolution, the coexistence of different groups has led to hybridisation. Most notably, modern humans interbred with Neanderthals and Denisovans. Gene exchange is often accompanied by the exchange of anatomical features noticeable in the fossil record. Yet previous studies have painted a blurred picture of the incorporation of certain features in different human populations. Neanderthals were thought to have evolved in Europe before later appearing in Asia about 70,000 years ago. However various findings over the last 10 years have begun to challenge this story, such as fossils in Israel with Neanderthal features from 400,000 years ago. Nesher Ramla Homo fills in a piece of the puzzle as an example of a late-surviving southwest Asian Homo population predating Neanderthals. This suggests that European Neanderthals were the remnants of a larger population that originated in Asia. Evidence of interbreeding between Homo sapiens and Nesher Ramla Homo about 100,000 years ago could explain why Neanderthals carried Homo sapien genes well before the two groups met in Europe. There is still much to learn about our evolutionary history. The discovery of Nesher Ramla Homo offers us new insight and indicates that the story is more complex than previously thought. Southwestern Asia acts as a crossroads between three continents – Africa, Asia and Europe – and so different human groups traveled and interacted through the area. Further work in the region could help us gain a better understanding of our own evolutionary past.
Written by Sophie Teall and edited by Diana Jorge.