Lateral descendents come from siblings, not direct descendents. Any credible publication should make that distinction. It was also my understanding that Lincoln does not have living direct descendents. And 299 "lateral descendents" is a very small number, actually.
And 299 "lateral descendents" is a very small number, actually.
If they had a genetic defect of the nervous system, maybe that cut down the number of surviving offspring for the whole extended clan.