An article published in the magazine “Trends in Ecology & Evolution” describes a research on the origins of modern humans. A scientific consortium led by Dr. Eleanor Scerri, a researcher at the Max Planck Institute for the Science of Human History, collected what’s believed to be evidence that modern humans’ ancestors were scattered across Africa, remained separate for millennia diversifying and then remixing to form the current Homo sapiens.
Probably the species Homo sapiens originated in Africa but there’s still much to be clarified regarding modern humans’ evolution. Basically, there has long been a search for a single place of origin from which modern humans spread initially across the continent and after many millennia started migrating to the rest of the world.
According to Dr. Eleanor Scerri’s team a reconstruction based on anthropological, archaeological, genetic and even climatic elements suggests a different story that could represent a case of speciation reversal. Evolution leads mainly to continuous ramifications with the emergence of new species. However, sometimes two populations that remained distinct for long enough to become even two different species can come into contact and, by hybridization, reunite and give rise to a further new species.
In this new reconstruction, the evolutionary lineage that led to the Homo sapiens species probably originated in Africa at least 500,000 years ago and the first traces of this species’ physical characteristics date back to about 300,000 years ago. What the authors of this research found is that early Homo sapiens fossils show a considerable diversity of physical characteristics and geographical spread.
The situation in the Pleistocene period may have been complex because various populations with different physical characteristics could have spread across Africa occasionally meeting and interbreeding. At the same time, it’s possible that they interbred with other species of hominins that we can’t identify because we have no traces of their DNA unlike what happened later with Neaderthals and Denisovans, of which instead it was possible to find samples of DNA of various individuals.
Dr. Eleanor Scerri pointed out that African stone tools and other artifacts show a distribution clustered in space and time. There’s a tendency to progress in the whole of Africa, but not in a single specific place or in a single period.
Professor Chris Stringer of the London Natural History Museum, one of the authors of this study, pointed out some anatomical and genetic elements. Early Homo sapiens fossils show mixes of archaic and modern features in different places and different moments. Genetic analyzes, including those of modern African populations, indicate levels of diversity that are difficult to reconcile with the idea of an origin occurring in one place.
The image (courtesy Philipp Gunz/Max Planck Institute for Evolutionary Anthropology, all rights reserved) shows on the left side a micro-CT scan of the Jebel Irhoud 1 skull dating back to about 300,000 years ago, perhaps the oldest Homo sapiens fossil, and on the right side the Qafzeh 9 skull dating back to about 95,000 years ago. The comparison shows the evolutionary tendency from an elongated to a globular shape.
The analysis of climate changes in Africa shows that there have been habitable areas that changed over time and were often isolated. The Sahara is the most striking example of an area that in ancient times was green and full of lakes and rivers while now is a desert. Some tropical regions that today are humid and green were arid in ancient times.
These environmental changes led various human populations to long periods of isolation in which they developed their own separate culture but also some specific physical characteristics. Subsequently, new changes led to contacts that made these populations mix up.
The conclusions presented by Dr. Eleanor are that modern humans’ evolution has been multi-ethnic and more complex than previously thought. Surely this research will stimulate arguments among paleontologists, paleoanthropologists, archaeologists and even scientists who work in other fields. If this theory were to be confirmed, it would prove even more that the success of the species Homo sapiens came as a result of a number of interbreedings between different populations and cultures.