Science matters: Human origins and migration, Richard Harwood

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Schematic map showing the migrations and timescales involved in the Recent African Origin model of human development

Scientific understanding proceeds by a continuous process of the falsification of current ideas in response to experiment and the gaining of new evidence. The field of human anthropology has demonstrated this re-evaluation process spectacularly over the past 60 years or so. Some 50 years ago, no one believed that modern humans could have originated in Africa. In this period, two models of the development and emergence of Homo sapiens have been put forward by different scholars:

‘Recent African Origin’ model (or the ‘Out of Africa’ model): currently the more accepted model, with backing from genetic studies, which proposes a single area of origin for modern humans. According to this model, modern humans evolved in East Africa (the Rift Valley region) and then began to disperse throughout the world roughly 50,000 to 100,000 years ago. This single-origin hypothesis is cited as having the scientific consensus as of the mid-2000s.

‘Assimilation model’: a model involving the multiregional emergence of modern humans, a more gradual spread of modern features, and a greater level of interbreeding between different hominid lines. This model suggested a wave of Homo sapiens migrating earlier from Africa and interbreeding with local Homo erectus and Homo neanderthalensis populations in multiple regions of the globe.

The accumulated evidence that has tended to support the ‘Recent African Origin’ model is wide-ranging, covering skeletal analysis of geological ‘finds’ and modern genetic analysis. This evidence is summarised in accessible detail in ‘Evolution: the Human Story’ by Professor Alice Roberts (2011), while a series of TED presentations on this topic area can be found at https://www.ted.com/playlists/84/ancient_clues

An interesting aspect of research into the history of human migrations is the Genographic Project initiated by National Geographic, whereby individuals can participate in such studies by contributing their DNA sample: https:// genographic.nationalgeographic.com/

However, the idea that modern people evolved in a single ‘cradle of humanity’ in East Africa some 200,000 years ago has been queried significantly by a recent report published in the journal Nature by Professor Jean-Jacques Hublin, of the Max Planck Institute (MPI) for Evolutionary Anthropology in Leipzig, Germany. Fossils of five early humans have been found in North Africa that show Homo sapiens emerged at least 100,000 years earlier than previously recognised. This report suggests that our species evolved across the whole African continent.

It is claimed that the discovery and analysis of these fossils excavated at a site in Jebel Irhoud, Morocco – consisting of

It is claimed that the discovery and analysis of these fossils excavated at a site in Jebel Irhoud, Morocco – consisting of skulls, teeth and long bones – would ‘rewrite the textbooks’ about our emergence as a species.

skulls, teeth and long bones – would ‘rewrite the textbooks’ about our emergence as a species. The newly-found material has been dated by hi-tech methods to be between 300,000 and 350,000 years old, and the skull form is almost identical to modern humans – the few significant differences in the skull structure being a slightly more prominent brow line and a smaller brain cavity. Evidence from the excavation further reveals that these ancient people employed stone tools and had learned how to make and control fire. So, not only did they look like Homo sapiens, they acted like them as well.

This research represents a potentially startling shift from what those who study human origins believed not so long ago, and could well lead to a convergence of the ideas involved in the recent models of human evolution and dispersal across the different continents. These are intriguing times therefore in the field of human anthropology, and illustrative of how scientific models develop and are refined by new evidence.

Roberts A (2011) Evolution: the Human Story, London: Dorling Kindersley