It's because we all start off as female in the womb until the Y chromosome kicks in and "tells" the fetus to develop to be a male. We also have milk ducts (non functional of course) and why the testes develop from the same tissue that the ovaries develop from. They've done experiments where they give a man the same hormones that cause lactation in nursing mothers and we can actually produce milk. Great. Now I can breastfeed my kid! h: