Genes

Well, as I posted in a thread months back, I hypothesize that the popular xenomorph and human-kind are genetically the same thing, sort of like how, in Neon Genesis Evangelion, the Angels and human-kind are genetically the same, but unable to co-exist. In the case of xenos and humans, the reason for the possibility of genetic similarity stems solely from how both were created by the Space Jockey. Of course, now that I re-read your question......if you're talking about how xenos are derived from humans by means of the xenomorph lifecycle, then yeah, because horizontal gene transfer is involved in how the unborn alien comes to be when gestating in the victim's body. But I assume lifecycle-related stuff isn't what you're inquiring about, but I just felt like pointing it out anyway.

No.

^^^ What takka_takka_takka said.

YES but I think they come from the same genetic stock!

What came first, the xeno or the egg?