Since I wrote the above, I've come to the conclusion that people are probably born with the tendency to be multiple, and there are likely lots of multiples out there who have no idea that the way they think is in any way different than the way anyone else does. Usually we have been thought of as being either spiritually gifted or possessed. And no doubt the multiples in question reflected the cultural expectations of them. It's not a surprising phenomenon. And for good reason - children have been taken from single mothers on the strength of a couple days dirty dishes.
Social pressures weigh on multiples just as heavily.
So the available sample is inherently skewed. In my case, by about 30 degrees. The interrogation continued, in it's innocently and unintentionally offensive way, much like the white baby in the old Uncle Remus fable, trying to scrub the black off a baby in the same tub. I've seen quite impressively credentialed sorts do exactly the same thing. And their response is to grab a bar of soap and try to scrub the black off.