Some commenters to my earlier post reason:

It [presumably discussion of possible innate gender differences in cognition] shouldn't be suppressed for political reasons. I think that a scientific issue, though, shouldn't be taught if there's not good scientific evidence for it. And I haven't seen good scientific evidence for this theory

I think the words "without proof" are implied from the second paragraph.

I.E. "when faculty tell their students that they are innately inferior, without proof, based on race, religion, gender or sexual orientation, they are crossing a line that should not be crossed"

I can see that as being fair.

Yet not every step in the scientific process can (or should) contain "proof" in any strong sense of the word. Scientific debates often present conjectures based on ambiguous evidence. The conjectures lead to responses, often equally conjectural. Evidence on one side or the other grows or shrinks. We often get something approaching "proof" only after decades of unproven conjectures have led to more evidence-gathering and more discussion.

This is especially so in areas (including biology and social science) where the evidence tends to be suggestive, not dispositive, and confounding factors are always potentially present. Even in math, though, where "proof" is indeed the touchstone, unproven conjectures are often made. If you couldn't say anything without "proof," whether logical proof, proof beyond a reasonable doubt, or even proof by a preponderance of the evidence as determined by some campus committee, scientific debate would be much curtailed.

I agree with Frank that professors who are teaching classes shouldn't teach as true statements that haven't been adequately proven. But Summers wasn't teaching a class, nor did he assert his claims as having been proven true. If professors can't express such conjectures — yet presumably their rivals would be quite free to present contrary conjectures, unless we're to completely eliminate public conjecture in science — then what sort of debate would we have?

Now perhaps conjectures that are entirely unbacked by any evidence, or backed by asserted evidence or reasoning that has been conclusively disproven through decades of open debate, are sufficiently implausible that we'd fault people who make them. But there is indeed a hot debate on the subject, involving some pretty serious people on both sides. There is evidence that some say points towards biological differences, and that others think is not probative enough (since it's so hard to isolate biological causes from social causes). There is the unquestioned reality that men and women are materially different chromosomally, hormonally, and physically, and that male and female animals of other species (where the explanation must presumably be biology and not "culture" divorced from biology) are often different in temperament and behavior. This at least suggests that looking for possible biological cognitive and temperamental differences and differences in distribution of various traits, alongside the chromosomal, hormonal, and physical differences, is not obviously a fool's errand — and thus is plausible fodder for conjecture and discussion of suggestive evidence, even in the absence of conclusive proof.

We have, as best I can tell from my layman's perspective, a serious and potentially intellectually exciting debate here. Shutting off one side, imposing on one side requirements of "proof" that bar the proposal of scientific conjectures, or for that matter imposing on both sides such requirements, strikes me as bad both for our knowledge of this subject and for scientific debate more generally.

UPDATE: In the post in which I first mentioned Prof. Barres' article, I linked to the article and also to an Edge.org debate between Steven Pinker and Elizabeth Spelke.

I probably should have also, for balance, linked to an article that takes the view contrary to Prof. Barres'; since I suspect that the attention on this thread has shifted from that post to this more recent one, I decided to add that link here -- it's to Kingsley Browne, Women in Science: Biological Factors Should Not Be Ignored, 11 Cardozo Women's Law Journal 509 (2005). Browne's piece is just a short version of some much longer work he's done, but I figure that shorter is often better for at least a first look at the matter. I stress again that I'm not claiming I know what the right answer is; I'm just trying to pass along pointers to both sides of the argument.