From The Pattern of Evolution
(pp. 4-5; 7)
by
© 1999 by Niles Eldredge.
Used with permission of W.H. Freeman and Company.
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Editor's note: In this eloquent and intriguing book, the renowned Niles Eldredge describes the history of scientific endeavor as the revelation of patterns, whether in the behavior of subatomic particles, the movement of the earth's crust, or the evolution and extinction of species. As patterns are found in both living and nonliving matter, Eldredge seeks the connections between the physical "matter in motion" and the flora and fauna of the earth. As he articulates here, he sees one very powerful connection in an example of the pattern of ecological succession - the gradual reestablishment of the Humacao tropical forest after being devastated by hurricane Hugo - starting with the emergence of the pioneer tree species Cecropia.
Eldredge's research has led him to believe that the fundamental impulse of an organism is simply to live, and that evolution has been a story of "economic" competition - that is, competition for resources. In this he opposes the school represented by Richard Dawkins' "selfish gene" theory, which maintains that evolution is driven by competition among genes and the impulse to reproduce. Eldredge finds that Dawkins' thinking "isolates biological evolution . . . from the physical realm," where he himself sees pattern-based connections between the two.
We join Eldredge just after he has experienced a crisis of faith, as the sight of a Cecropia momentarily convinces him that "Richard was right." However, while acknowledging the tree's reproductive skills, Eldredge, reflecting on the patterns he observes in the once storm-ravaged woods, ultimately finds in Cecropia not refutation, but confirmation, of his views.
Ecological succession does not happen without physical destruction of mature ecosystems. This is true whether we're talking of fires in grasslands and forests, of storm damage to coral reefs, of sandbars slowly traversing a bay and wiping out the invertebrate fauna living in and on the sediment surface or of a hurricane hitting a mature tropical rainforest. For Cecropia to sink its roots in, a clearing has to be made. And there is no way a clearing will appear through the simple lives and deaths of individual organisms. It takes an event, a physical event to trigger succession.
Ecological succession - where pioneer species colonize degraded habitat, eventually to be replaced as other species come to be reestablished - is a process that produces pattern. Hurricane Hugo's effect on El Yunque was an isolated event. But other such events - varying only in their intensity and coverage - produce extremely similar results. Over and over, through the entire tropics of the western hemisphere, the same pioneer species (such as my much-beloved Cecropia), show up first and are in due course followed by an orderly succession that differs only in detail.
Patterns in the natural world are extremely important. As we shall see, they pose both the questions and the answers that scientists formulate as they seek to describe the world: the nature and behaviors of entities such as atoms and continents, or organisms, species and ecosystems, according to one's particular bent and expertise. Science is a search for resonance between mind and natural pattern as we try to answer these questions. You look from the Yokahu Tower at the Cecropia stands on El Yunque and you know some devastating force destroyed large sections of the rainforest not all that long ago just as sure as if you were looking the bits of greenery that began peering through the ash on Mount Saint Helens a few years after its eruption. You might not be able to tell if this force was a tremendous wind causing blowdowns, or a fire (though a practiced eye surely could), but you know something set the ecological clock back to midnight, kicking off the standard reactions of normal succession.
So, too, with large-scale, deep-time patterns in earth and biological history. Patterns in the history of life have been suggesting for at least a half century that there are regularly occurring sets of conditions that seem to control evolutionary activity - dampening it, often for long periods, and triggering often rapid evolution at other times. Like ecological succession, evolution produces, not isolated events, but repeated patterns which hold clues to how the process works - specifically, how the physical world of matter-in-motion impacts the biological realm.
There are two morals here: First, short-term events, like ecological succession, produce well-known characteristic patterns, patterns that reveal the very nature of the process; second, so too do larger scale evolutionary events. And while evolutionary biologists willingly concede that isolated events affect the course of evolution (as when the dinosaurs became extinct when the earth was struck by one or more comets 65 million years ago), they have been slow to acknowledge that these sorts of events - all physically induced - produce repeated large-scale historical patterns that are just as regular, just as law-like, as ecological succession. The second moral - that all such ecological and evolutionary events are triggered by external, physical factors - is especially delicious. It suggests a metatheory (developed in the final chapter) that links such short-term ecological processes as succession with various other intermediate and truly long-term, global ecological and evolutionary patterns.
Finally, seeing that everything from ecological succession, through speciation and the radiation of large clusters of species (for example, "higher taxa," such as the class Mammalia) is triggered by (meaning "won't happen without") physical events (generally destructive) means one other thing: I needn't have worried. Dawkins's "selfish genes" are as incapable of triggering ecological succession as they are of directly causing evolutionary history.
Ten minutes walking in the Humacao woods, replete with more than one Gestalt switch, not to mention a final epiphany, reveals more than just the nature of the evolutionary process, it reveals the very basic way we all think. We encounter pattern; it impacts us, sometimes wholly subliminally; we wrestle with that pattern; and sometimes we end up seeing nature differently than when we began.
Finally, what other evolutionary patterns are there? How do they connect with ecological patterns, both large- and small-scale? And how do patterns in the history of the earth mesh with those in the history of life? What is the connection between the physical realm of matter-in-motion and biological evolution?
What, in the end, drives evolution?
As the answers to these and many other questions unfold, we begin to converge on a coherent theory that links the evolution of life with the physical history of the planet - not as a long series of isolated events, but in regular, repeated, law-like patterns that can be generalized into a coherent theory of physical and organic evolutionary process. Along the way, we also see how process is inferred from pattern - the fundamental ingredient of genuine scientific discovery.
Niles Eldredge is a curator in the Department of Invertebrates at the American Museum of Natural History, where he has been a research paleontologist since 1969. In the 1970s, with Stephen Jay Gould, he articulated the theory of punctuated equilibria, which states that evolution does not proceed at a gradual and steady pace, but rather in periodic short spurts of rapid development (and mass extinctions), between which are long periods of stasis.
Endlinks
Biology Rules - arguments from Niles Eldredge and Stephen Jay Gould against the recent reductionist approach to the study of human nature and culture. From the November 1998 issue of Civilization Online, from the Library of Congress.
Score One for Punk Eek - a Scientific American article from 1996 describing research that supports Eldredge and Gould's theory of punctuated equilibria.
Punctuated Equilibria - a detailed look at Eldredge's and Gould's theory from the Talk.Origins Archive.
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