What is meant by "form follows function" in biology?

In biology, "form follows function" means that, within an organism, structures are formed in direct correlation to what they are meant to do. For example, a cat's paw and a human hand have similar bones, but each are designed to function much differently.

The phrase "form follows function" is derived from the famous saying of skyscraper architect Louis Sullivan, whose exact words were "form ever follows function."

This is a particularly useful idea for biologists, who can see that structure and function go hand in hand, especially when it comes to cells, where the disruption of one aspect can lead to failure in another.