So Adam had an ex-wife.....

It has to be borne in mind that Lilith is a Sumerian, and on to Babylonian, female goddess/demon. Jewish academics would have picked her up during the Babylonian Exile and incorporated her into their writings using her as a trope for night terrors, cot death (or the 6BCE equivalent) etc. Interestingly, she doesn't appear as Adam's wife until around 700 CE and then gaining traction in the Middle Ages with The Zohar (Kabbalah)

This is one tradition there are many.

Still. That's a gene pool of just 3 individuals.