It is widely accepted that the ancestors of the Khoisan hunter-gatherers of the Kalahari separated from the ancestors of the rest of humanity 150,000 years ago; ancestors of all non-Africans separated from Africans on the order of 50,000 years ago; and ancestors of Native Americans separated from East Asians 15,000 years ago. In some cases, diverged branches of this diversifying human tree came back together and fused to form new populations. All of these events have left distinct genetic markers.
In fact, as the famed biologist L. L. Cavalli-Sforza once stated, though our history as a species is short, there is more than enough genetic information to construct ancestral trees. And, genetics has the power to reveal much more about you than just your racial and ethnic identity.
For example, by sequencing just a small portion of DNA, scientists can detect your biogeographical ancestry and even get a rough estimate of what your face looks like.