[quote=retlaw83]
do not have an explanation for how the first generations of them came to be
[/quote]
Of course there was an explanation. The inhabitants of Vault 87 were forcibly exposed to it on orders of Vault Tec, then spent the time since the Great War kidnapping and converting people. At the time of FO3, they've run out of FEV and are searching the CW for a new supply.
Note that I'm not defending this as a particularly good story. It's not. But it was there.
I agree though that Bethesda could have worked a bit harder to come up with good, original antagonists in FO3. The Enclave was a big plot step forward in FO2 from FO1, and FO1 was all about super mutants. Bethesda was far too conservative with extending the Fallout mythos.. I sincerely hope they do more to expand it in the next game.
