Humans Evolved From a Single Origin In Africa

Invisible Pink Unicorn writes "Researchers at the University of Cambridge have combined studies of global human genetic variations with skull measurements worldwide to show conclusively the validity of the single origin hypothesis. The alternative hypothesis contended that different populations independently evolved from Homo erectus to Home sapiens in different areas. The lead researcher explains, 'The origin of anatomically modern humans has been the focus of much heated debate. Our genetic research shows the further modern humans have migrated from Africa, the more genetic diversity has been lost within a population. However, some have used skull data to argue that modern humans originated in multiple spots around the world. We have combined our genetic data with new measurements of a large sample of skulls to show definitively that modern humans originated from a single area in Sub-saharan Africa.' The article abstract is available from Nature."

Comments

Re:Not so fast

[msaavedra]

I have a degree in anthropology. I recall some mathematical work...I didn't really understand it, but it was highly mathematical.

Typical anthropology major (I kid, I kid. I have a degree in anthropology, too).

I believe I've read the same or similar material. Here is a little more detailed explanation:

Population geneticists have observed more genetic variability within the African population than in other areas. This by itself doesn't mean anything, though. It could just be that the environment in Africa in the old days was pleasant enough that mutant genes had a decent chance of survival, while harsher environments in paleolithic Europe, Asia, etc could weed out genes much more efficiently through very vigorous natural selection.

There is another piece to the puzzle, though. Not only does Africa have a huge amount of variability, but that variability encompasses nearly all the variability found in other places as well. That is, the gene pools of Europe, Asia, etc are basically sub-sets of the African gene pool. Consider the following scenarios that could explain this:

1. The populations in various locations split apart, and evolved somewhat independently. By luck or some unknown process, those new mutations arising in Europe and Asia also arose in Africa. However, those arising in Europe did not arise in Asia, and vice versa.
2. The populations of the various continents split apart, but there is sufficient gene flow for mutations originating in one part of the world to spread to another. By coincidence or some process I'm not familiar with, the mutations arising in Africa spread to Europe and Asia, and those arising elsewhere spread to Africa. However, Europe and Asia have less genetic exchange, even with Africa acting as an intermediary.
3. Modern humans developed almost exclusively in Africa, fairly recently in geological time. They spread through the world, replacing earlier populations with little if any interbreeding. The migrating populations lost some of their genetic variability through natural selection in their new environments, or through forces such as the founder effect.

If think if you put this into mathematical language, you'd find option #3 is definitely the most likely. I wouldn't call it conclusive, though. After all, options #1 and #2 could be correct, if we discover some unknown processes that make them work without resorting to blind luck. In the meantime, though, my bet is on #3.