From the biological point of view, humanity is one of the most similar species compared to each other. The diversity of DNA in our bodies is not significant enough to divide people into several groups according to this factor. From a physiological perspective, there are no races in general; there are human beings whose DNAs are more matching than others. Race cannot be identified according to skin color; nonetheless, a social concept of race means classifying people according to their difference in appearance, like the eye shape.
The experiment at the beginning of the film illustrates why judging by appearance is not the optimal way to identify race. The differences in DNA are not correlated with skin color; that is why one dark-skinned man can have more similarities with a white-skinned woman than with someone of the same gender and origins. Biological characteristics are useful in order to identify the nationalities or the origins of the person but are unhelpful in the understanding race. DNA is not a source that can show belonging to a race. That is why, according to the information provided by the scientists in the film, biologically, this characteristic cannot exist in the modern world.