Human origins

Where did we come from, and how? We’ve long thought in terms of an evolutionary ‘tree’, but our origins in Africa are more like a braided channel. This idea provides a better fit to the data.

Based on fossil evidence alone, studies of human evolution have long agreed that modern humans evolved in east Africa and radiated out from there. But with the development of cheap, fast and reliable DNA evidence from modern populations, and DNA from fossil teeth and bone samples, it’s becoming clear that theorists can move forward again – and the picture seems a little more complicated than we thought.

On 17th May, Ragsdale and others published a research paper in Nature; ‘A weakly structured stem for human origins in Africa’; their evidence suggests evolutionary connections in populations that were separated for a while before recombining. So instead of an evolutionary tree (which most people were expecting) it seems that our human past is more like a set of braided channels.

Previous views on human evolution proposed a tree structure (branching but not recombining). However, the new ‘weakly structured stem’ model fits the data better than a tree model. It also explains the diversity of genetic forms in modern human populations, and shows that there is no single place in Africa where humans ‘originated’. After this process within Africa, humans spread out as show in the map.

See also:

• Nature – Short news article on the topic
• Ragsdale et al – The scientific paper in Nature
• Wikipedia article – Homo