“We have some concept of how on Earth life has evolved and how some simple beginnings led to creatures like ourselves with at least a certain level of intelligence. There seems to be a gradual increase in intelligence, and human beings at some stage surpassed other creatures, but we have no idea how inevitable that was. The four billion years of Darwinian evolution are now part of common culture. But most people, nonetheless, tend to think that human beings are in some sense the culmination. There’s no particular reason to think that intelligence couldn’t develop further. Astronomers know that our Sun is less than halfway through its life. It will be six billion years before the Sun flares up, engulfing the inner planets, vaporizing any life that remains on Earth. But any life that remains at that time will be life won’t be humans. It will be life at least as different from us as we are from bacteria. Because there is much time for future evolution on Earth and beyond before the Sun dies, as there has been to get from the simplest organisms to us.”

— Sir Martin Rees, What We Still Don’t Know: “Are We Real?” (Channel 4 series, 2004)