define categories? All humans can interbreed therefore we are all one species. divisions below this have difficulties of definition. Although much is said about races of man, the truth is that humanity is more of a spectrum than a set of races.....a quick glance at the variety of people in sub saharan africa will reinforce this. on the west, what used to be referred to as negroid races, on the east the nilotic races. You can almost tell how far west you are by assessing the mix of the two in the locals. It is like this all over the planet. So the real answer is that there are four divisions. Men, women, living and dead. Anything else is arbitrary.