Comment by landl0rd

You are talking about the kind of research we can do today. You can't really do case-control for medieval populations easily, nor surveys of criminals, nor of the broader population since everyone is several centuries dead. Natural experiments might work and are exactly one of the things we should see further researched in this area. Meta-analyses can't happen until there's other research to meta-analyze.

I think we're in violent agreement here; yes, this obviously bears further investigation. The way good science gets done is "We have some preliminary evidence that could support a certain hypothesis. We think people should do further investigation." Then you go do that further investigation to see if you can reject the null.

The alleles point, though, is weaker. You're not just looking at stuff like MAO-A activity, also CDH13, COMT, other variants. We actually have a pretty good set worth analyzing that are pretty well-characterized in research, so we don't have to depend on any one particular allele. We have a pretty good set of those that aren't associated with, I don't know, aggression in boardrooms.