I meant fertility in relation to other factors (including biological factors!); I agree that human psychology and culture are in part shaped by evolution, just as with any other species on the planet. The tricky thing here is that any empirical test of a proposition about human evolution must be "ex post facto". Ideally, scientists generate a hypothesis that states X changes Y, conduct an experiment to manipulate the X, and then observe the Y to test their hypothesis.
We can't do that here; the traits of a species have already been selected by evolutionary forces! --And evolutionary theory isn't alone in this; compare astronomy, geology, most topics in sociology. Often the topic of scientific analysis requires clever ex post facto reasoning, ideals of science aside.
That said, I agree that sociobiologists usually slide from reasonable ex post facto analysis to wild speculation about characteristics that could reasonably be explained by nonevolutionary factors (e.g., their goofy argument about rape as an adaptive trait).
Miles