Case in point - stubbers are largely the same as modern balistic weapons (They probably aren't any worse!), and if you get shot by one then you will know about it. In rules terms a 40k human has fair odds of surviving. It's my belief that modern humans would be toughness 2/strength 2/Initiative 2 in game terms, possibly even 1.
Just after posting I remembered the ogryns and rattlings of the IG. I missed those passing nods by the fluff writers towards evolution
That's a really interesting point though Azezel!
Well that really depends on how the environment on Earth changes. I've actually been discussing this concept with one of my ethics teachers and I'm glad I have a chance to bring it up here. So natural selection enables those with greater fitness to spread their genes around because those with less fitness are unable to pass on their genes. With the advent of rational human beings however, altruism assures advantageous genes are not spread like they once were. Because of this we do have a greater overall population but disadvantageous genes are allowed to remain in the gene pool.
Maybe this isn't really the place to get too deeply into it, but I would argue that having those 'disadvantageous' genes hanging around in the gene pool somewhere, having them reproduced and giving them a chance to mutate would actually increase the chances of some more interesting developments to occur.
Larger number of genes (must suerly) = larger number of potential changes.