Darwin developed his theory of evolution without understanding either DNA or genes. He referred to "blood" as the medium of inheritance. Lacking the concept of genes, he believed that an animal's traits would be passed to the next generation, but that its blood would be mixed with the blood of its mates. This explanation posed the problem that advantageous traits in a "fit" individual would be diluted in successive generations.
Does "blood" exist? If the question means "Is there a medium of inheritance, for which 'blood' was a partially adequate description?" then the answer is Yes. If the question is, "Is the concept of 'blood' as a medium of inheritance worth preserving?" the answer is No.
In the same way, one can ask whether "race" exists and get two different answers.