- "Many people think that because we have only one example of evolution, evolution on Earth, that we can't argue from it what kinds of things we're going to find on other planets. But actually that's not true, because on Earth, during the history of life on Earth, some things have happened very many times. There are very many creatures that have invented flight; the insects, the birds, the bats; all flying, they all are very different flyers, and they don't all descend from one animal that invented flight. They all invented flight independently, just as fur on the bumblebee and fur on the mouse, to keep them warm, is another invention. If we ran evolution again on this planet, such things would happen again; we wouldn't get birds, and we wouldn't get bats, doing the flying; but we'd get other creatures doing the flying, and we'd get other creatures with the fur."
- ― Jack Cohen
Convergent evolution besides being a major mechanism of evolution itself, is one of the major methologies of speculative evolution. When we see that eyes or hair have evolved several times on Earth, it becomes very plausible that they would continue being independently discovered further on in Earth history or during evolution on an alien world. Better than that even, we can examine the similarities and differences amongst these semi-independent occurrences, and get a better idea of what the general space of possibilities looks like.