Natural Detours

Is natural selection the prime mover behind evolution? Darwin’s great insight into the mechanics of evolution was that a population of creatures always has a lot of variation--more feathers here, less fat there, more urge to kill there--and some of these variations allow the individuals bearing them to thrive and have more offspring than others. After many generations these traits become more common among the population as a whole. If one imagines fitness as a beckoning peak on a given ecological landscape, then natural selection should be a process that moves species steadily uphill.