New Pan-African Model For Human Origins Proposed

Few fields of human endeavour are moving quite as quickly as that of anthropology and human evolution. On an almost weekly basis there are new papers being published that, instead of adding to or slightly finessing existing current models, require us to significantly rewrite what we thought we knew. I could easily dedicate this entire blog to human evolution and have no shortage of material. Two new papers in Nature (here and here) have produced just such an effect, but they are not without controversy.

Their analysis revolves around a tranche of ancient human bones and stone tools discovered in Jebel Irhoud in Morocco. Six bones, including a lower jaw and some teeth were discovered in the 1960s. At least 16 more bones from both adults and children were unearthed between 2004 and 2011.

What is not controversial is how old these specimens are as there are multiple, independent lines of evidence that all converge at around 300,000 years ago. The stone tools were made by knapping them from larger rocks, a technique that spread over Africa about 300,000 years ago. Some of the items were heated, possibly by fire. This allows the use of another technique, called thermoluminescence, which can tell how long it is since rocks have been heated. They got a result of 314,000 years for this technique. Furthermore, looking at the decay of radioactive uranium isotopes in the bones put a date of approximately 284,000 years on them. The 300,000 year figure, then, is pretty solid.

The controversy begins, though, with the morphology of the bones themselves and, therefore, whether they truly are a modern human or part of another, older species like neanderthals or Homo erectus.

Everyone seems to agree that the facial and dental features of the skulls are very much like modern humans, the brain cases, though, are certainly different. Modern humans have a high forehead with a domed brain case allowing plenty of space for our ample grey matter. These skulls, however, are longer and lower and have a smaller overall volume. For some anthropologists, this is a problem. They argue that they are, therefore, not Homo sapiens but something else; perhaps Homo erectus or another as yet undescribed species of human.

What to make of these new claims, then? Well, they are bold. Not only are they asking us to push back the origin of modern human evolution, they are also asking us to move it geographically. The current model says that we emerged in east Africa in the region of the Great Rift Valley.  These fossils come from Morocco in north western Africa. Hence, the authors are proposing a new pan-African model of our development.

Image taken from Hublin et al, 2017

This certainly isn’t impossible. We know for a fact that there were a whole host of different modern human species all over Africa by 300,000 years ago. It isn’t a huge stretch of the imagination to have some of them having a smattering of very modern characteristics. Perhaps those in Morocco are our direct ancestors, we’re unlikely to ever know for sure.

I don’t have much trouble pushing our origins further back in time; that date has been steadily forced back for decades now.

In summary, we certainly shouldn’t discount out of hand these new findings, but nor should we assume they are spot on. Bold claims need bold evidence and there is not yet a consensus accepting the evidence thus far presented. Scientific controversies are a Good Thing, though. They ensure careful scrutiny and vigorous debate. Ultimately, this new model will live or die in the arena of scientific debate. No doubt next week there will be another new paper for us to wrangle into our ever more complex origins story.


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