The city of Eymud holds the largest population of Unbreeders in the kingdom. The people of Iwa-Usum may no nothing of genetics, but they realise that people with black hair usually have babies of black hair. On that basis, they worked out that people with mental problems will probably also have babies with mental problems. The people believe it is because they were not blessed at birth by Iwa, rather WausumrudI, one of the desert god's myriad names. They believed all desendants would carry this curse, so decided to shut all people born with problems away from the rest of the kingdom.
But most of the population in Unbreeder colonies are old or infertile women. It is assumed all women instictively know how to look after people, no matter what age the woman or the cared for person is. So old women have the chanse to be mothers again, and infertile women have the chanse to be mothers.
The smallest population in Unbreeder colonies are homosexuals. Needless to say, there are only about enough homosexuals of either sex to fill one or two houses. As the priests of Iwa are uncertain on Iwa's posistion on homosexuals, the government lock them out of the way, just in case Iwa does one day proclaim homosexuals okay. Homosexuality is treated in much the same way as smoking on modern day Earth. Not outright illegal, but certainly frowned apon, discouraged and illegal in public places.
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I hope this isn't too modern day. I tried to make it as plausible as possible. But remember, you have to assume there was the equivilen to Down's syndrome, and even epilepsy in ancient times; infetile people and women who've menopaused; and the Greeks had homosexuals (but they were allowed, more or less).