Every now and then A Moment of Science likes to introduce a word for the day.

Today's Word of the Day is . . . spandrel.

"Spandrel" is a term from architecture. Imagine a dome that is held up by four arches, the way it's done in cathedrals. When you do this you wind up with some leftover space between each arch. That's a spandrel. Nobody planned for that extra space to be there, but if you're going to put a dome on top of four arches, you will always have it.

Since it was there, people started painting angels in the leftover space, and it became one of the nicest parts of many cathedrals. Biologist Stephen J. Gould used the term "spandrel" to express something that happens in evolution all the time. He gave the example of the Irish Elk. It had enormous antlers.

To hold up those huge antlers it developed big spines on the vertebrae at its shoulders. This made a hump on the animal's back. The hump later became useful as a mating device--bigger humps were sexy. But the hump wasn't developed in order to attract mates. It was just a bi-product of having big antlers. Later on, since it was already there, it developed into other uses as well. That's a spandrel!