[@NecroKnight], before somebody I know has an aneurysm, I humbly ask that you make one change to your post. 

So, the Black Dragons don't necessary know that their gene seed was originally from Vulkan. In fact, I don't think that's actually known. It's only been implied as a possibility. They were created during the Cursed Founding [url]http://warhammer40k.wikia.com/wiki/Cursed_21st_Founding[/url]. There's a good backgronud on them here: [url]http://warhammer40k.wikia.com/wiki/Black_Dragons[/url].