Tracing the Travels of the Human Race

We are all Africans in our DNA.

We all originally came from Africa. At least that is what a couple of new studies have claimed.

Now this isn't breaking news. Other studies have looked at people's DNA and proposed the "Out of Africa" hypothesis. What is different with these studies is how many people they looked at. And how much of their DNA.

One study looked at over 500,000 DNA differences in 438 people from 29 different populations. The other looked at over 600,000 differences in 938 people from 51 different populations. This dwarfs any other previous study.

All of this data showed that East Africans had the most diverse DNA. And that the further away a population got from East Africa, the less diverse their DNA was. So how does this show that we are all Africans at heart (or at least in our DNA)?

It has to do with the fact that DNA changes over time. Everyone’s DNA is a little different from when they were a fertilized egg because of DNA mutations.

If a change happens in the DNA of an egg or sperm cell, then it will be passed to the next generation. So the group that stays longer in one place will build up more of these changes. Their DNA will be more genetically diverse.

Imagine it is 50,000 years ago and our ancestors are all in Africa. These folks have been there for hundreds of thousands or even millions of years. Over this time, there were lots of individuals all mixing their DNA. And their DNA was changing slightly generation to generation.

Now imagine that a few people develop a bit of wanderlust. They’re tired of Africa and want to see what the Arabian Peninsula looks like. So a small group takes off and heads over there. And doesn't return.

This group, which will go on to found Asia's population, is not nearly so diverse as the group they left behind. And the smaller the founding group, the less diverse their DNA will be.

Now 50,000 years later, here we are. East Africans have continued to mix and change from their big diverse starting population. Asians have mixed and changed too but from a smaller, less diverse starting population. So the East Africans are more genetically diverse than the Asians.

Now imagine it is 10,000 years ago. A small group of Asians heads over to Alaska and doesn’t return. This starting group is even less diverse than the original group of East Africans. Which helps explain why Native Americans are genetically less diverse than Asians.

The studies were so big that they were able to make even finer distinctions (see the tree to the right). And as data continues to pour in (especially from companies like 23andMe and DeCODEme),
scientists will be able to refine ancestry even further.

Dr. Barry Starr is a Geneticist-in-Residence at The Tech Museum of Innovation in San Jose, CA.

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