Human Most Likely Origin Is "Somewhere in Sub-Saharan Africa?
18 Jul, 2007 07:00 pm
A new study published today in Nature shows new evidence that humans probably evolved in Africa. Interview with Dr Andrea Manica, lead author of the study.
There are several theories about the evolution of modern humans. The most favored one, even though it is still highly debated, is the idea of a single origin in Africa. The idea is that anatomical modern humans originated in Africa and have been staying there for a long period of time. That has been suggested by fossil evidence throughout researches in the past. Then, at some point, probably around 60 000 years ago, they moved out of Africa very quickly and colonized the whole globe. If the scenario was correct, we would have had a very stable population in Africa for a long period of time that would have actually cumulated diversity through mutations. As you’re moving away from that center, you are effectively loosing diversity because only few individuals would start from that core population and move out in the next area. The process got repeated several times, every time only some of the diversity of the population was represented by the migrants. We got two different sets, a genetic one and a morphological one. You may think that you have a glass full of beads of different colors, representing different types in terms of genetics or in terms of skull morphology. You are taking out a few and those are the migrants, the ones that are going to colonize the next area in the globe. When you are taking out only some of the beads, only some of the colors will be represented in your hand. You fill a new bowl up with the colors that you have now selected and you can restart the process. Every time you start a new bowl, a new population, your diversity is becoming less and less. We simply asked the question “do we find such decline from somewhere in the world?”. We started with Africa but then tested the whole world just to see if there were better places where you would see the origin of diversity, and then the progressive loss of diversity as you are moving away from the origin. That is how we found out that the most likely origin, the obvious place where it starts, is somewhere in sub-saharian Africa.
Do you think that these results will put an end to the debate on the origins of humans <[i>between scientists that claim that modern humans arose from a single African source and those who say that modern humans evolved everywhere]?
I would like to think but I am not sure it will be the case. I think it does sort of provide very strong evidence using two different kinds of evidence. The majority of geneticists accept the “out of Africa” hypothesis. Yet this is by no means universally accepted. There is still quite a lot of debate. We provide evidence that no matter which information you look at, whether you look at genetic or whether you look at skulls, you have to get the same results. The most important result of our paper is that we used both kinds of data and actually got something that is identical in terms of results. I think we pushed forward the debate in the direction of acceptance. I think that the only argument that will remain is that one episode of hybridization was Neanderthal. That is the work of Eric Trinkaus that has been often in the news. Some of the skulls we found are hybrids between modern humans and Neanderthals. Interbreeding between Neanderthals and sapiens was not happening on a regular basis and the product did not bring back into the population.
Andrea Manica is a researcher in the Department of zoology at the university of Cambridge
Interview by: Clementine Fullias
Manica A., et al, The effect of ancient population bottlenecks on human phenotypic variation, Nature, July 19, p 346