I speculated about this years ago and concluded there are several possibilities
1) It isn't a simple single gene trait
2) RJ didn't think it through
3) sul'dam do breed - I don't think we have seen anything to suggest otherwise
If it was a single gene trait, it could be maintained in the...
The continent of Seanchan is much bigger than that if the Westlands and doesn't seem to have undergone the same decline, so the population is much bigger, probably an order of magnitude. To counter this, they only brought a proportion over, we don't really have much information on how big that...