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… - Richard Dawkins

What, after all, is so special about genes? The answer is that they are replicators. The laws of physics are supposed to be true all over the accessible universe. Are there any principles of biology which are likely to have similar universal validity? When astronauts voyage to distant planets and look for life, they can expect to find creatures too strange and unearthly for us to imagine. But is there anything which must be true of all life, wherever it is found, and whatever the basis of its chemistry? If forms of life exist whose chemistry is based on silicon rather than carbon, or ammonia rather than water, if creatures are discovered which boil to death at -100 degrees centigrade, if a form of life is found which is not based on chemistry at all, but on electronic reverberating circuits, will there still be any general principle which is true of all life? Obviously I do not know but, if I had to bet, I would put my money on one fundamental principle. This is the law that all life evolves by the differential survival of replicating entities. The gene, the DNA molecule, happens to be the replicating entity which prevails on our own planet. There may be others. If there are, provided certain conditions are met, they will almost inevitably tend to become the basis for an evolutionary process.

We are not arrogant, not hubristic, to celebrate the sheer bulk and detail of what we know through science. We are simply telling the honest and irrefutable truth. Also honest is the frank admission of how much we don’t yet know – how much more work remains to be done. That is the very antithesis of hubristic arrogance. Science combines a massive contribution, in volume and detail, of what we do know with humility in proclaiming what we don’t. Religion, by embarrassing contrast, has contributed literally zero to what we know, combined with huge hubristic confidence in the alleged facts it has simply made up.

Next time somebody tells you something that sounds important, think to yourself: 'Is this the kind of thing that people probably know because of evidence? Or is it the kind of thing that people only believe because of tradition, authority or revelation?' And, next time somebody tells you that something is true, why not say to them: 'What kind of evidence is there for that?' And if they can't give you a good answer, I hope you'll think very carefully before you believe a word they say.