Ah, well, then, I apologize to the engineers, and to the arthritics (whom, like everybody, I have a good chance of being numbered among some day).

As to male nipples, I believe evolutionary theorists explain them as being too expensive to turn off, like the vermiform appendix or mole rats' eyes. At least (unlike the other two examples) they are some use: they are erogenous, and they serve to remind us males that we are mammals too.