Why Do Men Have Nipples?

I've been wondering that myself. Why do men have nipples? They don't do anything. They don't have any medical purpose. They don't even serve any artistic value (Remember Joel Schumacher's infamous Batman Forever suit? No? here's a reminder.). When I saw this book in Kinokuniya, I was somewhat intrigued (though not confident enough to buy it, especially with the inevitable random raising of the eyebrows) So when my ex offered me to borrow her's, how can I possibly refuse?

The book actually offers some great insight. The writers have answers to the most absurd questions like "Can you lose a contact lens in the back of your head?" or "If you are stranded on a desert island, should you drink seawater or your own urine?" and of course, "Why do men have nipples?"

So, why do men have nipples? The answer, quoted from page 30, is this:

We are mammals and blessed with body hair, three middle ear bones, and the ability to nourish our young with milk that females produced in modified sweat glands called mammary glands. Although females have the mammary glands, we all start out in the similar way in the embryo. During development, the embryo follows a female template until about six weeks, when the male sex chromosome kicks in for a male embryo. The embryo then begins to develop all of its male characteristics. Men are thus left with nipples and also with some breast tissue. Men can even get breast cancer and there are some medical conditions that can cause male breasts to enlarge. Abnormal enlargement of breasts in a male is known as gynecomastia. Gynecomastia can be caused by using anabolic steroids. So, if your favorite athlete suddenly develops man boobs and start winning medals then you know the reason why.