Spencer Wells, the author of “The Journey of Man” has been on his own journey, covering the world from Mongolia to Cambodia to Tanzania (twice) in the past few weeks. He’s checking in on the massive geneology project he’s overseeing, trying to determine the common ancestry of all mankind. In the course of this “spot tour”, he mentions he’s aware of just how different we all are: 6 billion people, 6,000 languages.
How do we explain this diversity? If we had a single ancestor – and we believe we do – how do we explain this vast diversity and our spread throughout the globe?
Darwin had an answer – he postulated that our early progenitors lived on the African continent. But he was talking about distant history, our common ancestry with apes. We know that Africa was disconnected from Asia until 16 million years ago, when we see a break in the ape population. But this is way earlier than the common ancestry of humans.
Linneaus started classifying all the species of the world, and ended up classifying 12,000 species, including homo sapiens. He defined subspecies as well, including H. Sapiens Afer (African), H. Sapiens Americanus (Native American) and H. Sapiens Monstrosus (a category for people he didn’t like, plus elves.) This model was largely unchallenged until quite recently. But now research on our DNA record allows us to a) find a common human ancestor and b) try to figure out how different groups diverged over time.
We’re able to do this by tracking mutations in DNA – when our DNA has transcription errors, these act as markers in human populations. By tracing mitochondrial DNA – which is only transmitted from mother to child, and Y-chromosome DNA – which is only transmitted from father to son – you can start building a geneological tree of our origins.
Building this tree shows us that the longest mutational legacy and the greatest human diversity is in Africa. This means we all share an African ancestry, and at some point, a group of Africans broke away from the continent and resettled elsewhere. We have a single African ancestor, and according to mitochondrial DNA, our common “Eve” was 200,000 years ago. Our common father is even more recent – 60,000 years ago, which suggests we were still all living in Africa at that time.
The reasons for our migration come from the weather. The last ice age came into play 70,000 years ago, burying North America under ice sheets, and drying the global climate. This massively increased desertification in Africa, reducing habitable area to very small patches. Human population crashed to less than 2,000. But our rebound comes from the rise of culture, which accelerated rapidly around 60,000 years ago. Suddenly we see the apperance of art, much finer tools, specialized hunting techiques, and, probably, complex language.
Our ancestors began migrating, following continuous grasslands, which acted as “moving meat lockers”. A huge grassland stretching from Germany to Korea was practically a highway for human migration. And some truly hardcore humans went north to Siberia and crossed to North America via a land bridge.
Wells documented much of this journey in “The Journey of Man”, which inspired a National Geographic film. The Geographic Society was so inspired, they offered to sponsor his work. Wells asked to increase their research population by an order of magnitude – they’ve built ten population genetics centers around the world, collecting DNA from indigenous populations. Individuals can participate by buying DNA kits online – the profits from those kits funds The Legacy Society, which works to preserve culture and language. So far, DNA from 25,000 indigenous people and 250,000 online volunteers has been collected, helping build a much richer map.