How much of the genome is shared among the family members? Part 3

Here we go from consanguinity into sociobiology in the sense that we can ask to each extent in societies they exist rules that from this very biological idea.

Haldane was a very famous biologist and once they asked him: “For what would you willingly die?”

and he said: “Well, I would die for 2 brothers, 4 cousins, 16 second cousins…” What he was saying, is that he would die for the amount of family members that would make his own genome survive. So this is exactly the numbers of individuals that carry the whole of his genome, statistically of course. The idea, then, is that we have this sociobiology thought, which is the study of the biological basis of human behavior, and of course that behavior, as any other phenotype, has a genetic base, and has been driven by natural selection.

Sociobiology explained very interesting points like altruism, the selection among family members or kin selection, but here we are going to see how this is important for the sociobiology of kinship. In the sense that we know that if you have children with a relative, the chance of having diseases is increased. And there are lots of avoidance of incest, meaning when the consanguinity is very high, a mother and a child, father and a daughter… In these cases is extremely strong the amount of diseases that the descendants would have. And there is this avoidance, not only in humans, that is culturally, but also in other species.

So there are many ways that have been selected through natural selection of avoiding that, recognizing for example who are your brothers and sister to not mating to them. Of course this is not something recognized by their minds in other species as it is not maybe also in humans, because it is very likely that in our case, our cultural taboos have at the very end, a biological base. To end up, we are going to do a view of how we share with our family these uniparental genomes. The part that comes only from the father, Y chromosome, and the part that comes only from the mother, the mitochondrial DNA.

Y chromosome it’s a full chromosome and mitochondrial DNA is a piece of DNA that comes outside the nucleus of the cell inside the mitochondria. The mitochondrial DNA is interesting because this comes only from the mother, and it has interesting properties. For example, we know that [it] does not recombine, meaning that the whole molecule is passed from the mother to their children, and only the females will pass it to the next generation. And it has been possible to redo the whole genealogy of all existing mitochondria in the world.

Here you have a tree in which all the mitochondria of all humans have a place within this tree, and the numbers is the place [in the mtDNA] in which there is a change, a substitution in the DNA, a single substitution; and what is interesting of this tree, is that, if you look at the deeper branches, these are exclusively of Africa and we are going to visit that to understand how the genome has helped to reconstruct human origins and human history. In this case, you can see how the mitochondrial DNA lineage, differences within the tree, is spread all over the world and this has been used for recognizing human origins and human migrations.

In my case, this is my mitochondria that is a mitochondria spread mainly in north Europe. And, to end up, we have the Y chromosome, but for the Y chromosome we are going to visit that in the next chapter.