Answers to your questions (and those of countless others), in order of presentation: 1. Yes, it is a social construct, the depth of which runs from our penchant for categorization to our defense(s) for doing the things we do. Historically, we have treated others according to how we perceive them: perceived worth; perceived intelligence; relevance to our personal station in life and the world as we have known it at any given point in time and other factors, as we have made them up, for our own convenience. 2. There do not appear to be any sort of such bases. If there were, we would have probably found (by now) that, for example, it is not advisable to transfuse blood from black people to white; white to Asian; native-American to black, and so on. There have been no cross-racial dangers that I know of, as long as the donor is otherwise healthy and has no disease or syndrome that would harm the recipient (think, e.g., sickle cell disease). 3. Again, I answer yes. Why? Because the act of making race an issue conforms with the reasons for doing so, as set forth in #1, above. If we were color-blind (in the social sense, not the physiological), there would be no rationale at all for racial categorizations. But that would have the world, as we DO NOT know it---and probably a better one, too. And that, dear inquirer, is as philosophical as it gets.

Science is the measure of a nature that is truly immeasurable, indivisible, or just one.
The future is absolute and philosophy will lead the way! =

"Race" has no meaning except that it is an equivocation fallacy made by the british to turn family into competition in order to justify nepotism and slippery slope for aristocracy.

That people have a tendancy to trust people that look like them and are sexually attracted to people with similar traits is a topic that does have some evolutionary basis. But figuring the perfect moment between nature vs nurture is probably impossibly difficult to pin.

The question i find most difficult to answer, at what point is it not considered "racist" to choose mates that carry similar traits.

I often hear complaints that pink women are hounded as racists for not wanting to date brown men on dating sites. Which is more racist? Pink women not wanting brown men or brown men wanting pink women?

One is an active process of hounding pink women where the other is a negative of just not seeking brown men.

At some point, you can apply a fallacy wherever you want if you're a believer of fallacy.