""It is often stated that human genetic variation is low compared to other mammalian species, and it has been claimed that this should be taken as evidence that there is no natural subdivision of the human population.""

 

that would make sense because our populations aren't isolated anymore.

in essence we poured all our variation into a large genepool, instead of smaller isolated ones. in a way we are "breeding out race" with our continuious intraracial mingling.

but between populations that have stayed solated, like people in papua new guinni and say....some small town in rural england.

there is quite some variation, even if it's only on the expression level.