We tend to get a distorted view of history as a long, boring past during which nothing much happened, and then a very short period of rapidly accelerating change leading up to the present. In reality, however, the Sun isn’t yet even halfway through its life cycle.
Despite that, people who predict things “a million years from now” are considered to be talking about the unimaginably distant future, but a million years is only a few dozen clock ticks of cosmological time. We as humanity are responsible for the future of not just the next few thousand years (the timescale on which civilization has so far existed) but for “spans of time six or more orders of magnitude greater than that.”
Over the truly long term, our posthuman descendants will become — not just second-generation intelligences — but thousand-generation or million-generation intelligences. He quoted Darwin on how no species can pass its likeness into the distant future unaltered; in a billion years of biological evolution, we’ve gone from bugs to humans, and technological evolution is a lot faster than biological. Our distant descendants will be not just strange, but completely alien to us.
During this century, we not only have unprecedented opportunity, but unprecedented responsibility. If the new technologies we build have a high chance of causing civilization-wide catastrophe (and Rees thinks they do) for the first time in history, then we are, all of us, are responsible for actively preventing that from happening, not just trying to predict it or understand it. The key thing here is the commitment to taking action to alter the future instead of just trying to predict it.