We are biologically 'programmed' to select mates for the best offspring. A very interesting topic. We also instinctively try not to mate those of 'antagonistic' or 'inferior' genes.<quoted text>That is the DNA activating perfectly ~ although we do know there are mutations and failures as such. Breeders worked out interbreeding issues and mutations quite some time ago, and there were certain references to certain breeds of people not breeding with each other, and although we probably don't know who is from which Tribe certain scientific tests will give couples advice on having children due to their DNA having problems with the next generation.
Fortunately I realized that sex does not imply reproduction (contraceptives) so my standards are not dictated by my 'sinful nature'. lol I am still a sucker for redheads though. LOL