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[ warhammer 40k ] Why do all the primarch looks like the natives of their planet?

So my question is why or how surely they should all look like the emperor considering they have his DNA but they all resemble their homeworlds people for example look at Khan and Vulkan and corrax so I just wanted to know how or a reason why?
gpt
The image of the Emperor you see pre corpse is only what he allows you to see, he can change his appearance to some extent to blend like he’s been doing his whole life. That’s why not he or his experiments are bound by the normal laws of genetics. As for why some Primarchs look completely different, for Vulcan it’s the environment in his home world that the radiation emits and causes humans that live there to look like that. Also think about how animals are shaped by their environment, so will humans as well after all some Primarchs have been living in those planets for at least a century. Corax has been living in an underground prison for all his childhood that’s why he’s pale. But you gotta remember this was planned by the Dark Gods to ensure the Primarchs survive and adopt a violent society to serve their needs.