Race certainly has some aspects that are socially, and not biologically, constructed but in its entirety race is not a social construct. Instead it is society that is a racial construct because different societies and nations exist and the societies they create is a reflection of their DNA. Compare Iceland and the Ivory Coast, Germany and Ghana, Canada and China.
Doctors and medical researchers know different medicines effect different ethnic groups in different ways. How can this be possible if racial differences are only skin deep?
All dogs are capable of interbreeding as are all humans. Many take this as proof positive of innate biological equality. But we do indeed kind ourselves if we believe all dogs are the same. Would you rather be in a fence with a Doberman or a Labrador Retriever.
No serious animal breeder, whether it be rabbits, cows, pigs, cats, dogs, or horses, seriously believes that all breeds are the same merely because they can interbreed.
And the two girls above are fraternal twins not identical twins which negates their argument as fraternal twins could indeed have separate fathers depending on how close their conception was.