But, getting back to the original point, the human penis certainly has two functions. I don't see why we're wasting our time with this obvious point.I didn't argue against that. I merely stated that one function, the excretion function, was essential for survival, and I threw in the sphincter reference as an illustration.
You countered "Why does "fitness" imply one and only one specific function?" with "How do you drive a single car down two different roads at the same time?"
It appears this was a foolish analogy, since clearly fitness does imply more than one specific function.