There is a tendency in discussing evolutionary psychology toward confusion over what should be the proper null hypothesis. To put it simply, what do we assume* in the absence of evidence for an hypothesis?
This confusion is not specific to evolutionary psychology. It is a problem whenever we talk about studying topics in which many of us already consider ourselves experts. Being human, we are, of course, all experts on what that means. Or we think we are. So we think we know what base assumptions about humanity we should use absent any evidence to the contrary.
The fact of the matter is, however, that we are not experts, not most of us. We haven’t studied the huge bodies of literature coming out of anthropology, psychology, and sociology that would be required to have to the first clue what kind of assumptions are warranted. Our assumptions are based on “Everybody knows” and some very simplified understanding of biology and living in a world in which variability is to a large degree defined as dysfunction. They are rarely nuanced or complex.
This means that when we hear someone arguing against a particular interpretation of data, when we hear someone say that a hypothesis was not supported, we tend to think that person is arguing for a null hypothesis that is…well, somewhat out there. Someone tells us that the data is insufficient to determine whether a particular difference observed between two groups is genetic, and far too many of us hear that person assert that there is no genetic influence on behavior. Genetic influence is treated as an all-or-nothing proposition.
I know. When I put it like that, it sounds a bit silly, but it happens with amazing regularity.