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All humans are descended from an original human population from a few hundred thousand years ago in Eastern Africa. As climates changed (along with other stuff), some populations emigrated to other areas. This happened a whole bunch over the time since then. These populations acclimatized to their areas using the principles of micro-evolution. For example the people who settled in Europe weren't synthesizing enough Vitamin D from sunlight so they lost the pigment in their skin. These lineages and adaptations are not the same thing as new species with evolution because we are all still the same species and can interbreed. When an individual from one area of the world reproduces with someone from another, they make a hybrid. There is so much hybridization that has occurred (especially where the social construct of Race pops up a lot in the U.S.) that the genetic basis for "race" is blurred. So "races" are real and there is a biological basis for it, but it's not the way most people think. It's not "Black race" vs "white race". We're all just varieties of the same thing; the same species.
There are no discrete races in humans: it's all one big spectrum, a giant continuum. There are multitudes of admixed populations and populations that adapted to environments somewhere in the middle.
