Legend has it that when Adam bit into that fateful apple, a piece of it stuck in his throat and became the familiar "Adam's apple." But, what does an Adam's apple really do for you? The Adam's apple is a prominent bump on a man's throat. It is caused by the underlying cartilage and ligaments of the larynx or voice box. The larynx protects the vocal cords from injury.
But, boys have vocal cords and a voice box, so why don't boys have an Adam's apple? Well, they do. But during puberty, a boy's vocal cords become significantly longer, allowing him to switch from soprano to baritone. These new, longer cords require a larger container, so to speak, so the larynx also grows to accommodate them.
The larger larynx is simply easier to see. This is also the reason that women do not appear to have an Adam's apple, although, of course, they do have one. Generally, women have higher voices than men: this means they have shorter vocal cords and a smaller larynx. Their larynx is just not as noticeable.
Also, women generally tend to have a greater percentage of body fat than men do. This fat hides the larynx and gives the neck a smoother appearance. Large or small, the larynx earns its keep protecting the vocal cords, but beware a direct hit to the larynx: it is still a sensitive area and is vulnerable to fractures.