The often very deep differences between those cultures should not be seen as divisions between people. The oneness of the human family is not only a spiritual reality, but a biological reality as well. Anthropology, physiology, psychology recognize only one human species, albeit infinitely varied in the secondary aspects of life. In particular, the insights of genetics and population science show that the human race is indeed a single species - a family in the literal sense of the word. This reinforces the spiritual truth of oneness and also points to practical ways in which it can be incorporated into science curricula.
Humanity meets the scientific criteria for a single species.
Several extensive studies of hybrid populations have been made and they show no evidence for reduction in viability, fertility, or functional efficiency in the first, second, or later generations of hybrids between unlike human populations. The genetic differences among human beings are slight compared to the differences that differentiate humans from any other species. The genetic markers that supposedly divide the human species into races represent only a minute fraction of our genetic endowment. Furthermore, the boundary between different races is not well-defined. No matter how one tries to divide humanity into races, there are always many peoples who do not fit neatly into any of the categories.