Board Thread:Warhammer 40k General Discussion/@comment-4851119-20140118095944/@comment-8881468-20150103231630

we agree that they are not clones, they are heavily modified in their genetic structure, their bone structure and whatnot else, however: each legion adaptation is unique

also we are not talking about  simple procreation and change over generations: we are simply talking about overwriting their genetic material with a superior code, enhancing it and making it like their primarch ( which is seen especially f.e. in the changesx in the melanchromatic organ of some legions/chapters or f.e. in the SW canines: the older they get, the more pronounced the features become.

do yourself a favor and do not compare apples to oranges