It is true; anatomically modern humans, Homo sapiens, emerged in Africa about 250,000 years ago. Since then, our ancestors have travelled and settled all over the globe, but there is actually very little genetic diversity among human beings. Researchers believe that this is due to a population bottleneck that occurred sixty to one hundred thousand years ago. The major differences we do see among humans, such as skin color and nose structure, probably result from the founder effect, in which all the descendants of a small group tend to have genetic resemblances.
The last major anatomical changes of humans, according to the fossil record, occurred between 400,000 years ago and 250,000 years ago, which is when Homo erectus transitioned into Homo sapiens.
Homo sapiens appeared in Africa about 250,000 years ago.