J. B. S. Haldane

The great evolutionary biologist J. B. S. Haldane was once asked what evidence could destroy his confidence in the theory of evolution. He replied, "Precambrian rabbits." This answer has become popular imagery in debates about evolution, and it's easy to see why. The idea of finding fossilized rabbits in rocks that are older than the dinosaurs is just plain weird. It would seem to suggest that evolution happened much faster than we think it did, or that rabbits evolved from a different ancestor than other mammals. Of course, the chances of finding Precambrian rabbits are extremely slim. Mammals didn't even evolve until hundreds of millions of years after the Precambrian. But Haldane's answer is a reminder that no scientific theory is perfect. There is always the possibility that new evidence will come along and force us to rethink our understanding of the world. So, if you're ever feeling smug about your knowledge of evolution, just remember the Precambrian rabbits. They're a reminder that even the most well-established scientific theories are always open to revision.