Which - considering that no one older than five dwells on why Auntie Fatima at the fish&chips shop has a beard - is one of the *truly* puzzling questions in life.
The answer to the male nipples question brings to mind the origin of the Y chromosome, and the mantra instilled in all first year Zoology students: Ontogenie Herhaal Filogenie (ontogeny repeats philogeny) - the development of the individual follows the development of the phylum. The 70s feminists were wrong - it's not the future that's female, it's the past.
Which brings us back to Auntie Fatima and her beard. At some point female hormones go into relative retreat, allowing their male counterparts to assert themselves more - bring Auntie Fatima her beard, and many other women the rampant libidos of their later years. Sadly, no accompanying increased proficiency in parallel parking has been observed.
But if ontogenic, and phylogenic, trends suggest that female is where we begin, not end, what does this predict for social trends which suggest that masculinity is under threat?