I thought Stephen Baxter made an excellent point about the changing nature of science fiction as science has progressed over the past century:
But science fiction has - rarely - been about the prediction of a definite future, more about the anxieties and dreams of the present in which it is written. In H. G. Wells's day the great shock of evolutionary theory was working its way through society, so Wells's 1895 classic The Time Machine is not really a prediction of the year 802,701 AD but an anguished meditation on the implications of Darwinism for humanity. As science has moved on, a whole variety of science-fictional "futures" has been generatedHe notes that today's science fiction is influenced by advances in biotechnology and information technology which have created the possibility of transhumanism, and the looming issue of climate change.
Kim Stanley Robinson similarly points out that science fiction "spring(s) from the realities of the time", but notes that "rapid technological change, volatile global politics and inevitable climate change all combine with contingency to make imagining our real future impossible."
I think that's what makes science fiction interesting to me - there are so many possible futures out there to be explored.
Also see comments by Ursula Le Guin, William Gibson, Margaret Atwood, and Nick Sagan.
Tags:science fiction, biology