Polar bear and brown bear are completely different species, not "races". As for hominids, only one subspecies remains, all others having been either destroyed or absorbed by the Homo Sapiens.
I have no clue what publications you have read, but scientific studies are clearly not among them. You have so far even managed to misrepresent the scientific method, itself, let alone genetic research. External physical attributes called "phenotypes", and they govern nothing more than a tiny handful of genetic strains. They are not even distant enough to qualify as breeds, as in those of dogs, which in turn are not genetically distant enough to qualify as subspecies.
[And I have read that afro-africans and east asians have more trouble with their offspring, europeans (and indians and arabs) being the (missing) link between them.]
I don't even know where to begin about all the things wrong with this sentence. Lets just start with fact that there is no scientifically valid data consulted about your reading material, whatsoever. All humans share identical biological reproductive behaviour. Trying to explain away cultural differences with biological factors became scientifically obsolete some 60 years ago.
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@ThorsomeTarmukas
Kindly, kindly do at least the most basic research on this subject. Look the damn Wikipedia page on the subject: https://en.wikipedia.org/wiki/Race_%28human_categorization%29
Polar bear and brown bear are completely different species, not "races". As for hominids, only one subspecies remains, all others having been either destroyed or absorbed by the Homo Sapiens.
I have no clue what publications you have read, but scientific studies are clearly not among them. You have so far even managed to misrepresent the scientific method, itself, let alone genetic research. External physical attributes called "phenotypes", and they govern nothing more than a tiny handful of genetic strains. They are not even distant enough to qualify as breeds, as in those of dogs, which in turn are not genetically distant enough to qualify as subspecies.
[And I have read that afro-africans and east asians have more trouble with their offspring, europeans (and indians and arabs) being the (missing) link between them.]
I don't even know where to begin about all the things wrong with this sentence. Lets just start with fact that there is no scientifically valid data consulted about your reading material, whatsoever. All humans share identical biological reproductive behaviour. Trying to explain away cultural differences with biological factors became scientifically obsolete some 60 years ago.