I've always pondered the "genetic utility" if you will of downs folks. I could imagine they play a real "symbiotic relationship" with their familial cohorts bringing lighthearted joy and other social softeners that add brightness to a group. It does come with costs however like people say with lifetime care, but the fact that these loving genetic subpopulations persist makes me wonder if they are not in fact anomalies but part of a richer fabric.
Probably not... but ancillary benefits like this can lower the selective pressure against trisomy 21, so that it's less likely to go away.
That's the thing. Something rare like Down Syndrome only has a very small selective pressure against it, and it's really easy for other effects to remove a fraction of it.
So things that seem ridiculous like this assertion or the "super uncle" theory about homosexuality are not so easily dismissed when one really thinks about them. Of course, there can be selective benefits from genes with a propensity for (forming trisomy 21, having homosexual individuals, etc) when the specific condition doesn't manifest.
