Public discourse on very long-term planning is riddled with inconsistencies. Mostly we discount the future very heavily — investment decisions are expected to pay off within a decade or two. But when we do look further ahead — in discussions of energy policy, global warming and so forth — we underestimate the possible pace of transformational change. In particular, we need to keep our minds open — or at least ajar — to the possibility that humans themselves could change drastically within a few centuries.
Our medieval forebears in Europe had a cosmic perspective that was a million-fold more constricted than ours. Their entire cosmology — from creation to apocalypse — spanned only a few thousand years. Today, the stupendous time spans of the evolutionary past are part of common culture — except among some creationists and fundamentalists. Moreover, we are mindful of immense future potential. It seems absurd to regard humans as the culmination of the evolutionary tree. Any creatures witnessing the Sun's demise 6 billion years hence won't be human — they could be as different from us as we are from slime mould.
But, despite these hugely stretched conceptual horizons, the timescale on which we can sensibly plan, or make confident forecasts has got shorter rather than longer. Medieval people, despite their constricted cosmology, did not expect drastic changes within a human life; they devotedly added bricks to cathedrals that would take a century to finish. For us, unlike for them, the next century will surely be drastically different from the present. There is a huge disjunction between the every-shortening timescales of historical and technical change, and the near-infinite time spans over which the cosmos itself evolves.
Human-induced changes are occurring with runaway speed. It's hard to predict a mere century from now, because what will happen depends on us — this is the first century where humans can collectively transform, or even ravage, the entire biosphere. Humanity will soon itself be malleable, to an extent that's qualitatively new in the history of our species. New drugs (and perhaps even implants into our brains) could change human character; the cyberworld has potential that is both exhilarating and frightening. We can't confidently guess lifestyles, attitudes, social structures, or population sizes a century hence. Indeed, it's not even clear for how long our descendants would remain distinctively 'human'. Darwin himself noted that "not one living species will transmit its unaltered likeness to a distant futurity". Our own species will surely change and diversify faster than any predecessor —— via human-induced modifications (whether intelligently-controlled or unintended), not by natural selection alone. Just how fast this could happen is disputed by experts, but the post-human era may be only centuries away.
These thoughts might seem irrelevant to practical discussions — and best left to speculative academics and cosmologists. I used to think this. But humans are now, individually and collectively, so greatly empowered by rapidly changing technology that we can, by design, or as unintended consequences — engender global changes that resonate for centuries. And, sometimes at least, policy-makers indeed think far ahead.
The global warming induced by fossil fuels burnt in the next fifty years could trigger gradual sea level rises that continue for a millennium or more. And in assessing sites for radioactive waste disposal, governments impose the requirements that they be secure for ten thousand years.
It's real political progress that these long-term challenges are higher on the international agenda, and that planners seriously worry about what might happen more than a century hence.
But in such planning, we need to be mindful that it may not be people like us who confront the consequences of our actions today. We are custodians of a 'posthuman' future — here on Earth and perhaps beyond — that can't just be left to writers of science fiction.