HOW COME? Why we have an Adam's apple

What's an Adam's apple for, and why do some have it while others don't? asks a reader.

A large Adam's apple can look like someone's swallowed a piece of fruit -- and it's lodged in his throat. But an Adam's apple isn't part of the esophagus, the tube that food passes through on its way to the stomach. Instead, it's part of the voice box (larynx), the place where sound production starts.

You might have noticed that little kids don't have Adam's apples, yet they can talk perfectly well. But when kids -- usually boys -- become teenagers, the mysterious lump often appears on the front of their neck. How come?

All of the different human voices we hear around us, in a restaurant, office, or school, start in the larynx. If you could see inside your neck, you'd realize that the larynx isn't really a box, but just the cage-like top of the trachea, or windpipe.

Like your nose, the stiff part of the larynx is made of cartilage, forming a boxy framework protecting soft tissues inside, such as the vocal cords. The vocal cords -- two bands of muscle covered in mucus membranes -- vibrate when air passes over them from the lungs. When the "cords" contract and shorten, they produce higher sounds. To produce lower sounds, the vocal cords relax and lengthen.

The smaller your larynx, and the shorter your vocal cords, the higher the frequency and sound of your voice. Which is why children's voices are higher than those of most teenagers and adults: Kids' vocal cords are usually less than a half-inch long.

But as children grow, so do their vocal cords. Bigger vocal cords would soon outgrow the small voice box of childhood. So the larynx changes, too, its cartilage shell enlarging like the shell on a growing baby turtle.

After the vocal tract's growth spurt, our necks may look different. The bigger cartilage cage can appear as a bump on the front of the neck, especially visible when swallowing. Presto: An Adam's apple.

So if everyone's larynx gets bigger, why do boys and men seem to have most of the Adam's apples? In boys, hormones like testosterone cause vocal cords to grow even more, making most men's voices deeper than most women's. Along with the cords, the voice box grows extra-large, too. So for boys, a cracking, changing voice is often accompanied by a wasn't-there-before lump on the front of the neck.

But women can have visible Adam's apples, too, especially if they have very little fat in their necks. Likewise, depending on neck structure and body fat, many men don't have prominent Adam's apples.