It is a biological necessity to shit.
However, I seem to have no faith in universal anatomy within a species, as I have convinced myself that certain people never have and never will poop. On the list are: Oprah Winfrey, Amanda LePore, Sarah Jessica Parker, and Ghandi - just to name a few.
I simply doubt that they have a digestive tract at all; or that some of them even eat (excluding the big O - and I don't mean Overstock.com). Until I see Miss Winfrey squatting on a white porcelain throne, straining, giving birth to the batch of cookies she "didn't eat" the day before, I cannot be convinced otherwise.