The psychic unity of mankind should preclude the existence of a miraculous genetic ability like this in only one in four hundred people: if it's possible, it should have achieved fixation. Ekman believes that everyone can be trained to this level of success (and has created the relevant training materials himself) but that his "wizards" achieve it naturally; perhaps because they've had a lot of practice.

This doesn't follow. Just because it's not a complex genetic adaptation doesn't mean it's environmental. Liar-detection-ability might just be an additive-effect quantitative trait like height or IQ, with truth-wizardry being the extreme right tail. This is consistent with evolutionary genetics, as Eliezer's psychic unity point only applies for adaptations with multiple interdependent (and therefore non-additive) genetic parts.