[Morgeruat]

I know the line from the star trek novels was that the Klingons had crossbred 1/2humans to deal with humans (and a similar race was also created for dealing with romulans) so that they would never see the "true" Klingons and would've instead dealt with something more similar to thier own race. This sadly was destroyed completely in DS9 after Gene died when they brought back the original Klingons now with head-ridges. (Gene Roddenbery of course always said that Klingons should've always had the head ridges, but budgetting didn't allow for the make-up) Still if you're going to try and reason it out without resorting to "it doesn't exist" tactics, or having the crew fail to notice the 1/2breed solution works pretty well.