It may seem strange, then, that wheels have never evolved in nature, but there are two reasons for this. First, there are natural limits to what kinds of things can exist in nature. Living things change slowly over time, a process called evolution by natural selection. This process can create many different answers to a problem, but it can't always create every answer that can be imagined. Also, the ways that new living things build themselves (a process called developmental biology) can't always create every kind of part that can be imagined. Second, wheels are sometimes less useful than other ways of moving, like walking, running, or slithering like a snake. For the same reason, some groups of people in the past have given up using wheels completely.