They had to exclude some of the Negroid DNA from the study, because it stood out (probably a matter of mixing with an absurdly archaic chominid, already after the rest of humans left Africa - only Negroes and a couple of Dravidian tribes (India) have genes that evolved separately from the rest of humans almost 2 million years, possibly erectus). They were able to identify which parts of the modern human genome are not shared with other hominids - meaning that they were not present in the ancient ancestors we shared with Neanderthals and Denisovans, and were not introduced into the human gene pool through interbreeding with these ancient humans. They also detected excess blocks of Neanderthal and Denisovan haplotypes unique to South Asian genomes. Finally, we point to human-specific changes likely influenced by selection since the separation from archaic hominids, many of which are involved in brain development. Nathan Schaefer of the University of California, San Francisco, and colleagues created a tool called the Speedy Ancestral Recombination Graph Estimator (SARGE), which allowed them to estimate the ancestry of individuals.