I found this site where you can trace your ancestry back using DNA
A person’s paternal ancestry can be traced by DNA on the Y-Chromosome or yDNA for short. Only men have a Y-Chromosome, which they inherited from their fathers and will pass on to their sons.
A person’s maternal ancestry is traced by mitochondrial DNA or mtDNA for short. Both men and women possess mtDNA, but only women pass it on to their children.
We all inherit our mtDNAs from our mothers, but not from our fathers. Your mother inherited it from her mother, who inherited it from hers, and so on back through time. Therefore, mtDNA traces an unbroken maternal line back through time for generation upon generation far further back than any written record.
Research at Oxford University and elsewhere over many years has shown that all of our maternal lines are connected at some time in the past and that these connections can be traced by reading mtDNA.
One striking finding was that people tended to cluster into a small number of groups, which could be defined by the precise sequence of their mtDNA. In native Europeans, for example, there were seven such groups, among Native Americans there were four, among Japanese people there were nine, and so on.
there were lots of ancestral mothers, and there are about 36 world-wide, we know where abouts they lived and how many ten of thousands of years ago,because dna changes and so people are able to calculatelong how long agothey lived .