THE SPORT OF ROWING ward change for the better, a steady, inevita- ble improvement from the primitive to the more and more advanced. But just as scientists studying the origin of species have learned, evolution in the world of nature is much more nuanced and complicated. It is rarely steady, and pro- gress is rarely inevitable. And, as in all of science, unanswered questions will always remain. Punctuated Equilibrium which evolutionary change occurred only very slowly. He illustrated his concept of punctuated equilibrium not as a ladder but as an invert- ed cone20 model, narrow with little variation and few species at the bottom, and then slowly widening and diversifying almost imperceptibly over time . . . until some cata- strophic global event eliminated most of the diversity by wiping out all but the very har- diest survivors. A new equilibrium would then establish itself around whatever was left. Slow diversification would begin anew, and another inverted cone structure would eventually develop. Each catastrophic event would form a revolutionary boundary, one Age ending abruptly with a massive global extinction, and the next Age developing with an entirely dif- ferent cast of major characters. Indeed, the fossil record is Punctuated Equilibrium After each global extinction, the few survivors quickly evolve to fill the voids. The late Stephen J. Gould, a teacher at Harvard University, posited a distinctive view of evolution in his book, Wonderful Life. Rather than thinking of the Earth’s evolutionary past as the classic ladder of progress,19 moving ever onward and up- ward, from simple to sophisticated, much like the cliché monkey-to-man illustration at the beginning of this chapter, Gould pro- posed the concept of punctuated equilibri- um. By this he meant that the history of life has been made up of a series of long spans of relative stability and equilibrium, called “Ages” or “Periods” by scientists, during 19 Gould, p. 37 punctuated by many revolutionary boundaries, preceded and followed by long periods of relative stasis. Revolutionary boundaries have a common thread: the world acquires a new set of challenges for some reason, and not every species can make the cut. Something suddenly increases the competition, leading to survival of only those best suited for or best able to adapt to the new challenges. For example, after an enormous meteor strike in Central America abruptly changed world climate around sixty-five million years ago, primitive mammals survived and adapted, but most dinosaurs didn’t. That marked the end of the Cretaceous Period. More recently, Neanderthal man lived successfully in Europe for twenty-five thou- sand years. That is five times the length of 20 Ibid, p. 39 15
