In Part I, "Mystery of the Mind," the narrator makes the claim that what makes us human is our big brains. At one point, he says the following:
Ever since Aristotle, philosophers have wondered what makes us different from the beasts. Their answers, that man is a political animal, a thinking animal, a tool making animal, can now be discarded. Now when we ask what makes us human, we can answer "this gene and that one and that one." We can begin to write the recipe for making a human being.
Specifically, the gene ASPM is pointed out as the gene that is responsible for brain growth, and hence for the distinctively large human brain.
Mutations in the ASPM gene are the common cause for a condition known as autosomal recessive primary microcephaly. Even though microcephalics do not have a large brain as a result of mutations in the ASPM gene, the narrator says that they are human just like you and I.
Are these claims compatible? If what makes us human is our big brains, or the ASPM gene that is responsible for brain growth, then wouldn't we have to say that microcephalics are not human, since they don't have big brains because of mutations in that gene? On the other hand, if we say that microcephalics are human, even though they don't have big brains because of mutations in the ASPM gene, then wouldn't we have to say that it is not our big brains or the ASPM gene that make us human?