Thinking About Aliens Stretches the Imagination

The virtue of thinking about life elsewhere is that it forces us to stretch our imaginations. Can we think of alternative solutions to biological problems already solved in one particular way on Earth? For example, the wheel is a comparatively recent invention on the planet Earth. It seems to have been invented in the ancient Near East less than ten thousand years ago. In fact, the high civilizations of Meso- America, the Aztecs and the Mayas, never employed the wheel, except for children's t...