Ancestry is the science of determining an individual's ethnic origins.
From the first individual to the present day, about 500 generations have passed (each generation is 25 years on average).
Based on the relative low mobility that human beings have had until our centuries, most of our ancestors lived for generations in the same region, interacting and having families among members of the same community, region ...
Thanks to this regional "homogeneity", we can classify contemporary populations into ethnic groups, which are distributed throughout the planet. And with this, we can compare the DNA of an individual with the references of each of these ethnic groups, weigh how similar the individual's DNA is with respect to those ethnic groups and with this estimate the ancestral origins in proportions / percentages.