Ancient humans left Africa earlier than thought, new discovery shows
17:07 BST, July 12, 2018
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20:40 BST, July 12, 2018We do not come from just one part of Africa but from many, says a team of scientists. In other words, our human ancestors in Africa were scattered across the continent. They were also diverse in culture and form.
A scientific consortium found that human ancestors were scattered across the African continent. For the most part, settlements did not communicate with each other.
Diverse habitats and shifting environmental boundaries such as deserts kept them apart. Forests are also examples of shifting environmental boundaries.
Long-term separation gave rise to a surprising diversity of human forms, said team leader Dr. Eleanor Scerri. Dr. Scerri is a British Academy Postdoctoral Fellow at the University of Oxford. She is also a researcher at the Max Planck Institute for the Science of Human History.
Dr. Scerri added that the mixing of these diverse human forms ultimately shaped modern humans.
According to the Max Planck Institute: “The patchwork of diverse fossils, artifacts and environments across Africa indicate that our species emerged from the interactions between a set of interlinked populations living across the continent, whose connectivity changed through time.” (Image: adapted from Max Planck Institute. Image Credit: Yasmine Gateau.)
Our human ancestors – Africa
Scientists across the world agree that our ancient ancestors, i.e., the first ones, came from Africa. However, we have paid less attention to how our human ancestors evolved within the African continent. Africa is a huge place.
Many anthropologists and archaeologists had assumed that our early human ancestors came from one place. In other words, we originated as a single, large ancestral population. They also assumed that our ancestors exchanged technologies and genes randomly.
An article that Dr. Scerri and colleagues published in Trends in Ecology and Evolution (citation below) challenges that assumption.
The team studied the bones, stones, and genes of ancient humans. They also created reconstruction models of Africa’s habitats and climates over the past 300,000 years.
Our human ancestors used these Middle Stone Age cultural artifacts from southern and northern Africa. (Image: Max Planck Institute)
Human ancestors – many origins
Dr. Scerri, lead author, said:
“Stone tools and other artifacts – usually referred to as material culture – have remarkably clustered distributions in space and through time.”
“While there is a continental-wide trend towards more sophisticated material culture, this ‘modernization’ clearly doesn’t originate in one region or occur at one time period.”
If you study human fossils, you also get a similar story.
Co-author Prof. Chris Stringer, a researcher at the London Natural History Museum, said:
“As with the material culture, we do see a continental-wide trend towards the modern human form, but different modern features appear in different places at different times, and some archaic features are present until remarkably recently.”
Co-author, Prof. Mark Thomas, a geneticist at University College London, said:
“We see indications of reduced connectivity very deep in the past, some very old genetic lineages, and levels of overall diversity that a single population would struggle to maintain.”
Our human ancestors’ skulls were elongated while those of modern humans have a globular shape. (Image: adapted from Max Planck Institute. Image Credit: Philipp Gunz)
A biological, cultural, and ecological patchwork
The scientists looked at the past environments and climates of Africa, which gave a picture of isolated habitable zones. They were also shifting habitable zones
The researchers wanted to understand why our human ancestors were so subdivided. They also wanted to understand how, over time, these subdivisions changed.
Habitats change over time
Many inhospitable parts of Africa today were ideal habitats for humans at the time.
The Sahara desert, for example, was once wet and green. The Sahara had lakes and rivers which interlinked. There was also abundant wildlife.
Conversely, some wet and green areas today were once arid deserts. These shifting environments forced animals and humans to migrate within the continent.
Trends in Ecology & Evolution says the following regarding this image: “Note that similarity can increase with distance under some circumstances, for example when similar habitats are separated by considerable distances, with areas of different habitat types being located between them.” (Image: adapted from cell.com)
Our human ancestors adapted
Our human ancestors would have gone through several cycles of isolation due to the shifting nature of habitable zones. These shifts led to local adaptation.
As they adapted, they also developed a unique material culture and biological makeup. Subsequently, they mixed genetically and culturally.
Co-author, Dr. Lounes Chikhi, of the CNRS in Toulouse and Instituto Gulbenkian de Ciência in Lisbon, said:
“Convergent evidence from these different fields stresses the importance of considering population structure in our models of human evolution.”
“This complex history of population subdivision should thus lead us to question current models of ancient population size changes, and perhaps re-interpret some of the old bottlenecks as changes in connectivity.”
Dr. Scerri concluded:
“The evolution of human populations in Africa was multi-regional. Our ancestry was multi-ethnic. And the evolution of our material culture was, well, multi-cultural.”
“We need to look at all regions of Africa to understand human evolution.”
In another recent study, archaeologists discovered that humans had migrated to Asia hundreds of thousands of years earlier than previously thought.
Citation:
“Did Our Species Evolve in Subdivided Populations across Africa, and Why Does It Matter?“ Eleanor M.L. Scerri, Mark G. Thomas, Andrea Manica, Philipp Gunz, Jay T. Stock, Chris Stringer, Matt Grove, Huw S. Groucutt, Axel Timmermann, G. Philip Rightmire, Francesco d’Errico, Christian A. Tryon, Nick A. Drake, Alison S. Brooks, Robin W. Dennell, Richard Durbin, Brenna M. Henn, Julia Lee-Thorp, Peter deMenocal, Michael D. Petraglia, Jessica C. Thompson, Aylwyn Scally, Lounès Chikhi. Trends in Ecology & Evolution, July 11, 2018. DOI: 10.1016/j.tree.2018.05.005.