(Distributions having fat tails, that is.) Evolution, as usually presented -- e.g., by Darwin himself -- talks about *gradual* changes happening over hundreds/thousands of generations. As Moore's Law shows, even gradual change, if extended to enough generations, can produce dramatic change when viewed with enough historical perspective. Nevertheless, I contend that the most dramatic evolutionary changes occur at *bottlenecks*, where 80-90-95% of the population is wiped out, and the few remaining individuals have one or more features which might not have had any (or perhaps only a very modest) effect under "normal" times, but suddenly become the only thing that matters for survival. Assuming that the rest of the genes of these survivors are more-or-less independently distributed, then normal day-to-day evolution will continue to weed out "bugs" in the rest of these genes which are more common, while the one or two features that provided survival at the bottleneck are now shared by *all* of the remaining population. For example, essentially all humans have 5 fingers on each hand. This is quite bizarre, as under "normal" circumstances, having 3,4, or 6 fingers would seem to provide about the same survival advantage as having exactly 5 fingers. Suppose that there was a population bottleneck where survival depended upon have *at least* 5 fingers, and all of the survivors had 5,6,7,8, etc. fingers. More normal evolutionary pressures might then have eliminated those individuals having more than 5 fingers, but the gene pool as a whole would "remember" vividly the bottleneck event which wiped out everyone having fewer than 5 fingers. Note that these population bottlenecks don't have to happen very often. Indeed, it is estimated that the last great bottleneck for the human race was perhaps 70,000 years ago. Exactly which features enabled survival in that bottleneck isn't known, but whatever it was, this feature was clearly was a *rare* feature that suddenly became crucially important for survival. This means that really understanding evolution is going to exceedingly difficult, as some of the most important events are also the rarest events.