Wendy Orent in Aeon:
We think of evolution, described by Charles Darwin in 1859, as a slow dance: nature chooses the best-adapted organisms to reproduce, multiply and survive in any given ecosystem. As organisms adapt to changing ecological circumstances over millennia, the varieties best-suited to the environment thrive, allowing species to emerge and evolve. This is the process known as natural selection, or differential reproduction, which simply means that the organisms best-adapted to their particular, immediate circumstances will pass on more genes to the next generation than their less-well-adapted conspecifics (members of the same species).
Permanent change, of the kind we see in the fossil record, takes more time. Just look at the plodding trajectory of the several-hoofed Hyracotherium, a dog-sized forest-dwelling mammal that gradually lost its side toes (four on the front legs and three on the back) as the central one enlarged. It took 55 million years for it to evolve into the large, single-hoofed, grass-feeding horse we know today.
But sometimes evolution happens fast. As the biologists Peter and Rosemary Grant at Princeton University in New Jersey showed in their studies of Galapagos finches, small beaks can change into large beaks in a single generation, depending on climate conditions and the type of food to be found on those harsh islands. The small-beaked birds might die out, while the large-beaked prevail, for a while at least. But those rapid changes aren’t often permanent. Though the Grants might have witnessed the evolution of an entirely new, heavy-bodied finch species, many of the changes they saw in finches’ beaks were reversed, again and again. Changes in vegetation could mean that large beaks become a handicap. This shifting process – small changes over short periods of time – is called ‘microevolution’.
The evolutionary biologists David Lahti of Queens College at the City University of New York and Paul W Ewald of the University of Louisville both argue that there’s nothing exceptional about fast evolution.
More here.