How Science and Genetics are Reshaping the Race Debate of the 21st Century:
http://sitn.hms.harvard.edu/flash/2017/science-genetics-resh...Here is good article that explains it more clearly:
Genetic Similarities Within and Between Human Populations
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1893020/
>The proportion of human genetic variation due to differences between populations is modest, and individuals from different populations can be genetically more similar than individuals from the same population. Yet sufficient genetic data can permit accurate classification of individuals into populations. Both findings can be obtained from the same data set, using the same number of polymorphic loci. This article explains why.
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>The fact that, given enough genetic data, individuals can be correctly assigned to their populations of origin is compatible with the observation that most human genetic variation is found within populations, not between them. It is also compatible with our finding that, even when the most distinct populations are considered and hundreds of loci are used, individuals are frequently more similar to members of other populations than to members of their own population. Thus, caution should be used when using geographic or genetic ancestry to make inferences about individual phenotypes.