Hi TD what I meant to say is I think maybe I should distinguish two levels to my discussion of social construction. On one level it should be emphasized that race as a category is highly problematic from an empirical standpoint for the reasons you mention. Even the slight differences among populations that actually exist at a genetic level do not correspond to any historical taxonomy of race. That's why Cofty was in the absurd position of claiming his picture of black runners proved race really exists, but he couldn't name the race. He finally offered "west African" which is not a category of race I've ever seen used. It's a geographical location, which made me suspect he really didn't understand what he was attempting to defend. Which he basically admitted in the end when he said he's not actually interested in defending the word race. It's as if when hearing the words "social construction", different black and white faces flash before some people's eyes and a common sense malfunction alarm bell goes off in their brain that tells them it's all rank stupidity. Of course differences exist, of course it's genetic. But anthropologists wouldn't argue that differences don't occur at a genetic level, only that such differences among populations don't correspond to any racial system either proposed or usefully imagined.
As you say the social construction of race is hardly controversial in the social sciences. In fact it's boringly orthodox. So I wanted to distinguish between categories in the world which seem to have a strong base in physical reality, like different kinds of fruit, and racial categories which depend more on politics, history and religion rather than physical features or genetics.
But at the same time I tend toward a strong social constructionist view of world which would in a sense take issue with the proposition that even apples and bananas are absolute categories. At a basic level every category humans apply to reality is socially constructed, even the most apparently self-evident "facts" about the world. Take an extremely basic example: what does reality consist of? Until a few hundred years ago the almost universal view was that reality consists of material and spirit. Now the secular assumption is that reality can be explained purely in material terms. Spirit has been marginalised but not entirely eradicated because the statement "the universe is material" only makes sense if there is "spirit" to contrast with material. So materialism oddly relies upon spirit for its meaning. What actually exists has not changed, but how people view it has changed fundamentally, just by the way we talk about it, construct it.