User blog comment:Cullen's are HOT!!!/Renesmee and Jacob (Question)/@comment-72.253.202.187-20111212053043/@comment-79.22.121.81-20111212202731

Agreed with you that there's just not enough info in the series to say anything either way.

But, if shapeshifter are _not_ human, what are they? Remember that those who do not phase are indistinguishable from ordinary human beings, so much so that it has been decided not to call them shapeshifters. And for what we know, we have ho idea how the extra chromosome pair appears - whether there are already 24 at conception, or because one of the regular human chromosomes split during the buildup to first phasing. The way I see it, shapeshifters are just turbocharged humans, not something fundamentally different.

Vampires, well, I get the feeling that what is called turning is a sort of metamorphosis induced by the venom (ain't it a pretentious word? - virus might have fit better.) I have no idea why two chromosomes should split, but again much of it seems just turbocharging a human being... And can't really argue against hybrids being infertile.