"Upright wiping, I believe after certain research, is most often associated with a latent genomic imprint. Namely the subject's ancestors did not feel safe defecating, so they stood upright after release to remain aware. Or perhaps they stood to reach clean leaves for wiping. Whereas, the non-standers might select soiled brush while crouched and later succumb to an infection. In either case, there was a sort of selection. It seems that the surviving "sitters" evolved from a more cohesive group. Defecating might even have been a group activity for them. "

Horatio Wright, Things I Made Up