How did humans (as a whole) develop a extreme pyschological and physiological rejection of anything concerning faecal functions? Those include personal, familial and even those with regard to other species, whatever they may be. I fart....you say "you stink....that's terrible". Your dog may roll around in another animal's faeces, or even eat it. "C'mon Fido....Gotta wash you now....naughty dog" is your reply. Various species of fish and marine animals thrive on excreta of other sea dwelling creatures. Numerous land based animals use other animal's faeces as a tool for hunting their prey or marking territory. I ask this for one reason. I have been working with autistic children and adolescents for over 15 years. Mainly (not exclusively) their cognitive response to either their own, or others' excretory processess are basically neutral.