The paradox of the visibly irrelevant

Natural History, Dec-Jan, 1997 by Stephen Jay Gould

But a cynic might still hold: Fine, I'll grant you substantial observable evolution in the frenzied little world of bacteria, where enormous populations and new generations every hour allow you to monitor 10,000 episodes of natural selection in a manageable time. But a similar "experiment" would consume thousands of years for multicellular organisms that measure generations in years or decades rather than minutes or hours. So we may still hold that evolution cannot be observed in the big, fat, furry, sexually reproducing organisms that serve as the prototype for "life" in ordinary human consciousness. (A reverse cynic would then reply that bacteria truly dominate life and that vertebrates represent only a late-coming side issue in the full story of evolution, however falsely promoted to centrality by our own parochial focus. But we must leave this deep issue to another time.)

I dedicate this essay to illustrating our cynic's error. For obvious reasons, bacteria may provide our best and most consistent cases, but measurable (and substantial) evolution has also, and often, been documented in vertebrates and other complex multicellular organisms. The classic cases have not exactly been hiding their light under a bushel, so I do wonder why the urban legend of evolution's invisibility persists with such strength. Perhaps the firmest and most elegant examples involve a group of organisms named to commemorate our standard bearer himself -- Darwin's finches of the Galapagos Islands, where my colleagues Peter and Rosemary Grant have spent many years documenting fine-scale evolution in such adaptively important features as size and strength of the bill (a key to the mechanics of feeding) as rapid climatic changes force an alteration of food preferences. This work formed the basis for Jonathan Weiner's excellent and best-selling book, The Beak of the Finch -- so the story has certainly been well and prominently reported in both the technical and popular press.

Nonetheless, new cases of such short-term evolution still maintain enormous and surprising power to attract public attention -- for interesting and instructive, but utterly invalid, reasons as I shall show. Let us consider the three most prominent examples published during the past year. (One derives from my own research and publication, so at least I can't be accused of sour grapes in the debunking that will follow -- although I trust that readers will also grasp the highly Positive twist that I will ultimately impose upon my criticisms.) The coincident geography of all three cases formed no part of my intention for this essay. I did not even know that the editor of Natural History had planned a special issue on the Caribbean. But all three cases -- Trinidadian fishes and Bahamian snails and lizards -- happen to fall within the spatial focus of this issue. As I said, measurable. short-term evolution is not a rare phenomenon at all, urban legends notwithstanding. I shall briefly describe each case, then present my two general critiques of their prominent reporting by the popular press, and finally explain why such cases teach us so little about evolution in the large, yet remain so important for themselves, and at their own equally legitimate scale.