How did races arise and what conditions facilitated their formation?

In total, there are 4 main races of people on our planet. All races have the same DNA, although at first it was believed that it is different for representatives of different races. Changes occurred in the course of a long life in a certain area. For example – the Negroid race has dark skin and dark hair, which protects from heat and ultraviolet radiation. There may also be differences not only in skin color and external differences, but also in various immunities. It is also associated with adaptations to life in a certain area from a peculiar climate.