Origins of the humans. Part 3

Here you have a similar plot of the principal component analysis, in which you can see the different color for different European populations. And, as the original publication said, genetic variation mirrors geography in Europe. You can see that genetic plot, the principal component plot, mirrors, is very similar, to the geographic map. Meaning that there is a clear stratification in the geography and we can recognize differences. Another way of analyzing this amount of data, and making that easy readable and understandable, is what we call the Analysis of admixture or Admixture analysis. In which we can plot, each individual from different populations, and separate a given number of ancestry components.

For example, in this plot we have all worldwide populations, and each line is an individual divided by different regions. Here you can see how clear, the African population is from the other, and here, you can also see that some of the populations presents stronger differentiations, and that are some individuals having mix ancestry between the two populations. Here is the same plot, but instead of seeing just a single one, here is when you see, when you take, the overall human genome variation, and you divide that in two components, three, four, five,… and when increasing the number, you get more colors and you get more distinctions.

Here, again, you can see in all the cases the dynamics of the populations that have produced this kind of graph to see how the present genome variation was produced in our past. The cases of admixture are very clear. Here, for example, in this plot what we have are the Africans and Europeans, and we have a lot of individuals just in between. These are, the African-Americans. And for each individual you can even count the amount of admixture, for one population or the other, and this is what you can see here, in this analysis of the local ancestry.

We are working out in Nama individuals of the San group, in which you can see, for the genome of an individual, which part of this specific individual has the ancestry in his own population, and which part come from external inputs, from Europeans or from other African populations. And here, this is something similar for a set of 41 of these San individuals. In which you can see the San component, but also the admixture with Bantus and Europeans. Overall, with this kind of analysis, we have been able to trace back our origins and our history. The main points are the followings. We have the African origins of modern humans. This origin is recent, in the last around hundred thousand years.

There is an out of African migration that was at the base of the expansion, initially in Asia. There is a spread through South Asia, the peopling of Australia, much earlier on the expansion into Europe and Central Asia. And, late, migration in the Americas. Then we have the peopling of the northern hemisphere, and then we have more complicated issues, more movements, historically known movements that can also be detected and measured in genetic terms. In general, when we see a map like that of the world, we have to recognize that this is a genetic map. These expansions have been traced back by our genetic understanding of the variation of humans.

And this information has been put in form of history of the human kind. So, this initial African origin, the initial expansion in South Asia, the expansion into Australia, then the expansion in Europe, and into the North, then the expansion into the Americans and the expansion all over the word. We have seen how we have been able to trace back our own history, based on the genome, on genetic data, on the genetic analysis. To obtain this picture, it has been needed a huge amount of data, a huge amount of genetic analysis, a huge amount of computation. But at the very end, a very general view of our past is very clearly emerging.