DNA has changed archeology in a lot of ways. Humans get spontaneous somatic mutations (normally of minor things like very small dental changes) at a known and rather constant rate, so it is possible to trace when a population became isolated from the source population and diverged, as the mutations get amplified over time, so one can compare two populations and their divergence and come up with a timeline.
The mitonchondrial DNA was a major breakthrough, as it doesn't even require complete cells to derive the mitochondrial genome. Mitochondrial Eve is indeed african and all of us carry her lineage, since it does not change through reproduction but is passed unchanged to the next generation... but our nuclear dna is a different matter, as it is subject to endless recombination and mutations over generations. certain populations have specific markers so ratios of "this or that" of known populations can be used to determine how much of one ancestral populations markers are present. That is what tripped up the north dakota nazi... his nuclear dna has 14% sub-sahara african markers.
Many northern europeans, native americans and oriental populations carry almost none or no african nuclear DNA, so in the mixing pot sweepstakes, they diverged without much back-crossing. But millenia of raping and pillaging in war usually introduced "marker mixing" so most everyone is more of a mutt than they probably suppose. Some scientists have predicted that the recessive trait of blue eyes is on the way out due to populations seldom being isolated any more.
(Moronosoros rex can disregard, as the principles of evolution are outside his fog cloud)
