Conversation with Francesc Calafell. Part 3

So, the idea of the African origin of modern humans came from the mitochondrial DNA study. To which extent this has been supported by other kind of data? It’s supported by the rest of the genome, it’s supported also by the Y chromosome but in other areas of the genome we see other processes going on such as introgression from archaic species that we don’t see in mitochondrial DNA or in the Y chromosome. And doing the same thing for the Y chromosome, do we have also an ancestral Y chromosome? Where and when?

Its more recent it’s about 70-80 thousand years ago and it may not be in East Africa but in West Africa where we’ll find the first split of the different lineages of the Y chromosome. Are there populations living today having the most ancestral part of this genealogical tree for mitochondrial or for Y chromosome and which populations are them? Yes, in the case of the mitochondrial DNA it’s mostly hunter-gatherer populations in Africa both in East Africa and in South Africa, and that is some particular populations in East Africa that speak Khoisan languages and that relates them to the Khoisan people in South Africa.

In the case of Y chromosome, it’s a little bit more diffused but the first split actually has been found in a mam from Cameroon if I recall correctly. So is more in Western Africa. So, going not so far away from our time, the Y chromosome also has been used –you have several works on that– to trace back ancestry related to surnames. What’s the meaning of that? In most societies surname is inherited from the father just as the Y chromosome is. Of course, we should not be so naïve to ignore some exceptions because there are false paternities, there are adoptions and in some cases there’s a transmission of the maternal surname, but these exceptions are also interesting.

So, the basic idea is that we can study a system of markers that are culturally inherited –surname- side by side with a marker that is inherited biologically, genetically – the Y chromosome. And putting them together we may know…, we may investigate particular family history and that’s of interest for many individuals who want to trace their origins. As scientist we want to go one step beyond and try to understand questions related to the entire surname system.

For instance: why are some surnames clearly much more frequent than others? Why some surnames are rare? And using the Y chromosome we can count how many times a particular surname was founded, and we see both in Britain, and in Spain, and in Catalonia, that the most frequent surnames are also the most diverse. This means that they were founded multiple times, they were invented multiple times. Think of surnames like Smith which refers to an occupation. The second most frequent surname in Britain would be Jones which means the son of John and there were of course multiple men called John and would have this derivation. There’s also… I was mentioning before these exceptions and we may quantify them using genetic information.

And this gives us information about human behaviour, about how many children each generation receive their Y chromosome from a man and their surname from a different man. And in different cultures it’s been seen that this figure is stable at around 2% per generation. And it has also practical applications. If you have an unknown biological sample say from a crime scene, you could think of predicting the surname of the man who left that particular sample. And we’ve shown in our studies that we would be able to do that in 60% of the cases but we would be wrong 20% of the times, which is certainly not a figure that would allow to have some conviction in a court. Okay.

Thank you very much. We have seen today that going from the individual into the social structure,

into the origins of humankind, just using a small fraction but very informative of our genomes: the uniparental which are the mitochondrial DNA and the Y chromosome.