One fifth of people alive a millennium ago in Europe are the ancestors of no one alive today ... the remaining 80 per cent are the ancestor of everyone living today. All lines of ancestry coalesce on every individual in the tenth century. [loc 1941]
Genetics offers good counter-arguments to racism, and to issues of caste in India (not just a product of colonisation); however, as Rutherford points out, a lot of the insights promoted by companies such as 23andme is little more than 'genetic astrology'. (My own genome still fascinates me though: it is one thing to know that one is descended from people in the distant past, quite another to be told of the traces they've left in my body.)
Rutherford is occasionally wrong though ...
If by some incomprehensibly reality-defying mutation a child was born with the nascent power of flight... their freakishness would probably render them an unlikely sexual partner. [loc. 4601]Now google 'wingfic' and reflect on 'unlikely sexual partner'.