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.

latitude: 0.213671, longitude: 16.9849

  • http://www.indiana.edu/~ensiweb Larry Flammer

    I saw your latest post on the QUEST blog about how comparing DNA traces early human migrations. It is one of the clearest, brief explanations for this analytical process that I’ve seen. It struck me how beautifully this shows the process of differentiation-in-progress through genetic drift and the founder effect (in contrast to basic natural selection). Are there sufficient samplings of DNA from the major populations that you mentioned (east African, Asian, and Native American) – or even made-up “samples” reflecting their differences – that students could compare and, with appropriate prompts, be walked through the discovery of early human migrations and the peopling of the planet?

    I am the webmaster for ENSIweb (living in San Jose), and would like very much to add such a lesson to our website (Evolution and the Nature of Science Institutes) at http://www.indiana.edu/~ensiweb In addition, as you may know, the CSTA (California Science Teachers Association) will be holding their annual meeting here in San Jose in late October. I will be doing 3 workshop sessions (if they are all accepted), including one where students discover mid-chromosome 2 telomere DNA showing that our chromosome 2 was formed from the fusion of two shorter chromosomes still found in apes today, and another comparing DNA samples that show that the closest living relatives of cetaceans are hippos.

    It may be too late for you or The Tech to add a workshop on the DNA evidence for early human migrations (unless it’s already scheduled, either at the convention, or at the Tech during the convention). If that’s the case, perhaps I could take a little time to include that material in one of my sessions.

    BTW, having watched the Tech mature over the years (I taught CP Biology at Del Mar High School for 38 years), I am very impressed with the leadership and ideas that you have apparently added to the Tech’s repertoire, going more deeply into the biotech realm than they had before. My compliments to you.

    Larry Flammer

  • Linus Hollis

    I’m impressed with how simplified you made things, but the timelines don’t mention Australians [and how they encountered the Asians to become the Polynesians] or the Ancient Ones of North America, who got here on the backs of mammoths 18-22000 years ago after their homeland on the floor of what is now the Mediterranean sea flooded. I’m only 1/16, but the history is very interesting.

  • http://www.thetech.org/exhibits/online/ugenetics/ Barry Starr

    I can only mention so much in a blog! I mostly wanted to focus on how scientists figure out ancestry history from DNA data. I should have included a link or two about the ancestry itself. I like https://www3.nationalgeographic.com/genographic/atlas.html as a nice beginning link.

    PS I love the image of men riding mammoths. Is there any archaeological data that supports that?

  • Pingback: Explosive hypothesis about humans’ lack of genetic diversity | QUEST Community Science Blog - KQED()

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Dr. Barry Starr

Dr. Barry Starr (@geneticsboy) is a Geneticist-in-Residence at The Tech Museum of Innovation in San Jose, CA and runs their Stanford at The Tech program. The program is part of an ongoing collaboration between the Stanford Department of Genetics and The Tech Museum of Innovation. Together these two partners created the Genetics: Technology with a Twist exhibition. You can also see additional posts by Barry at KQED Science, and read his previous contributions to QUEST, a project dedicated to exploring the Science of Sustainability.

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