This is commonly stated but seems more driven by ideology than science. People's racial identity is near to perfectly correlated with their genetic identity as can be ascertained with a very limited number of genetic markers.

And essentially all of species related biology would be a 'social construct' by such logic. The difference between entire species is often poorly defined. Different species can even interbreed and produce fertile offspring such as a liger. Or take the Australian Dingo which is literally just a wild dog, but it's not classified as one for quite arbitrary reasons.