We know that we sapiens cohabited the Earth for a long time with other Homos, among them the Neanderthals, the Erectus, the Desinovans. Two theories try to explain the extinction of all Homos that were not sapiens, the last one (florensis) being extinct 12,000 years ago. In the theory of miscegenation, sapiens were moving from Africa to other regions and mixing. Thus, Europeans are a mixture with Neanderthals and Chinese a mixture with erectus while the Australian us a mixture with the Desinovans. In substitution theory, on the other hand, different Homos not only did not mix but also repel each other. The miscegenation theory has very serious political and social consequences since racism can be understood as a mere consequence of a genetic abyss generated by the different mixtures. In contrast, the substitution theory seems more likely since intolerance is a hallmark of sapiens and our ancestors may have at the very least immeasurably hampered the survival of all our human cousins. Apparently we mix but very little since, for example, Australian aborigines have 6% Denisovan DNA and Middle Eastern populations have 1% to 4% Neanderthal DNA; since we were able to extinguish most animals in the last 200 years, it is not difficult to imagine that we were able to destroy some human species. However, we still cannot say with absolute certainty that we were responsible for the extinction of all our cousins. Anyway, whether through miscegenation or substitution, we are extremely intolerant when we do not recognize ourselves in others.