"[Martin Rees] may be right. If we were to go back 5 million years, as intelligent apes, and ask ourselves "What is postbiological life?" I think the answer is it's not a concept that would possibly mean anything. So we've had... 4 billion years of life on earth, and it's come up with an enormous wealth and variation, but it's all organic and... the chances of it coming up with humans? I can't put a number on that. ...I don't think there's an inevitability that life, once it's started will give rise to a human-like intelligence or beyond that. I think there's nothing inevitable about it, and if we just go back a few million years on earth, there was nothing inevitable about it. So I, personally would still look for organic life, but... I'm not sure that would be the easiest thing to find. It may be that it's easier to find, yes, nano aliens or something."