A good theory explains a lot but postulates little.

A good scientific theory is one which is falsifiable, which has not been falsified.

The theory of evolution by cumulative natural selection is the only theory we know of that is in principle capable of explaining the existence of organized complexity

We should not live by Darwinian principles. But Darwin explains how we got here.

[Evolution is] a theory in a special philosophical sense of science, but in terms of ordinary laymen's use of language, it's a fact, ... Evolution is a fact in the same sense that it's a fact that the Earth is round and not flat, [that] the Earth goes round the Sun. Both those are also theories, but they're theories that have never been disproved and never will be disproved.

My main reason for scepticism about the Huxley/Sagan theory is that the human brain is demonstrably eager to see faces in random patterns, as we know from scientific evidence, on top of the numerous legends about faces of Jesus, or the Virgin Mary, or Mother Teresa, being seen on slices of toast, or pizzas, or patches of damp on a wall. This eagerness is enhanced if the pattern departs from randomness in the specific direction of being symmetrical.