They have an oral tradition you wouldn't believe. Their children memorize family histories back two hundred generations. They know who they're not supposed to marry. Maria blinked in the insect-laden night. But they must have a few mistakes.
Someone lies to their husband.
If they've made mistakes, none of them have survived. We haven't found any autism, or Down's. He finally gave her that three-armed sideshow freak look again. Maria clenched her teeth, clenched her fists. That's what it is.