There's a new Fallout 3 FAQ at The Vault, the Duck and Cover community's ultimate source of Fallout information. Here are a few good quotes:
Why are there super mutants on the East Coast? Shouldn't they all be in California?
According to a Fallout ending, most super mutants fled to the East after the death of the Master. It's not implausible for at least some them to have reached the East Coast after 115 years.
The death of the Master was the first major step towards ending
his mad dream of conquest and enforced peace, but it is the destruction
of the Vats that neutralizes the mutant threat. Without the ability to
create more mutants and enforce their harsh brand of justice, the
mutant armies flee to the east, beyond the no-man's land.
Does it mean that they're not sterile, then?
No, super mutants are definitely sterile.
ZAX in Fallout says:
Additionally, as the gametes of the reproductive system consist
of 'half-cells' using split DNA, they could be perceived as 'damage' by
FEV, which would 'repair' them, rendering the subject sterile.
And according to Vree:
While the process by which this happens is uncertain, it does have some severe side effects. Chief among them is sterility.
If you have something good to add, the head on over!
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