Evolution happens through natural selection when mutations for traits occur that give an organism a survival and/or reproductive advantage and get passed on to the next generation, thereby giving this new generation of organisms survival and reproductive benefits that allow them to generally outcompete those that do not have these traits. Niggers developed from Homo Erectus as the rest of humanity.

Homo erectus certainly had advantages compared with the great apes he could walk upright, and so use his hand more, he had opposable digits which are useful for making tools, etc. Also the IQ is obviously higher than that of apes. Although a species does not need to have a high IQ or have pro-social traits to be biologically successful.

As man developed throughout the hundreds of thousands of years he came to resemble modern day man through a long series of gradual changes. The ancestors of the human races today separated geographically and occupied different areas. Generally speaking niggers stayed in Africa. To answer your question (I suppose) of why niggers are so stupid and crime-prone compared to most of the rest of the races it is because they were not selected so much for intelligence and conscientiousness during the latest long periods of human evolution.

Whites and East Asians lived in cold, harsh environments where food was scarce and co-operation, intelligence and conscientiousness were highly selected for. In Africa even during the last Ice Ages niggers were not affected so much by the cold, as food was much more ubiquitous and easier to obtain, it was much easier to survive and they were not selected for intelligence or conscientiousness as much. So niggers today are akin to the ancient hominids, as they did not experience as much evolutionary changes.