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In 1916, Frederic Clements, one of the founding fathers of ecology, called a community of creatures such as the beech hardwood forest an emergent superorganism. In his words, a climax formation is a superorganism because it "arises, grows, matures, and dies....comparable in its chief features with the life history of an individual plant." Since a forest could reseed itself on an abandoned Michigan field, Clements portrayed that act as reproduction, a further characteristic of an organism. To any astute observer, a beech-maple forest displays an integrity and identity as much as a crow does. What else but a (super)organism could reproduce itself so reliably, propagating on empty fields and sandy barrens?

Superorganism was a buzz word among biologists in the 1920s. They used it to describe the then novel idea that a collection of agents could act in concert to produce phenomena governed by the collective. Like a slime mold that assembled itself from moldy spots into a thrusting blob, an ecosystem coalesced into a stable superorganization -- a hive or forest. A Georgia pine forest did not act like a pine tree, nor a Texas sagebrush desert like a sagebrush, just as a flock is not a big bird. They were something else, a loose federation of animals and plants united into an emergent superorganism exhibiting distinctive behavior.

A rival of Clements, biologist H. A. Gleason, the other father of modern ecology, thought the superorganism federation was too flabby and too much the product of a human mind looking for patterns. In opposition to Clements, Gleason proposed that the climax community was merely a fortuitous association of organisms that came and went depending on climate and geological conditions. An ecosystem was more like a conference than a community -- indefinite, pluralistic, tolerant, and in constant flux.

The wilds of nature hold evidence for both views. In places the boundary between communities is decisive, much as one expects if ecosystems are superorganisms. Along the rocky coast of the Pacific Northwest, for instance, the demarcation between the high tide seaweed community and the watery edge of the spruce forest is an extreme no-man's-land of barren beach. One can stand on this yard-wide strip of salty desert and sense the two superorganisms on either side, fidgeting in their separate lives. As another example, the border between deciduous forest and wildflower prairie in the midwest is remarkably impermeable.

In search of an answer to the riddle of ecological superorganisms, biologist William Hamilton began modeling ecosystems on computers in the 1970s. He found that in his models (as well as in real life) very few systems were able to self-organize into any kind of lasting coherence. My examples above are a few exceptions in the wild. He found a few others: a sphagnum moss peat bog can repel the invasion of pine trees for thousands of years. Ditto for the tundra steppes. But most ecological communities stumble along into a mongrel mixture of species that offers no outstanding self-protection to the group as a team. Most ecological communities, both simulated and real, can be easily invaded in the longer run.

Gleason was right. The couplings between members of an ecosystem are far more flexible and transient than the couplings between members of an organism. The cybernetic difference between an organism such as a pollywog and an ecosystem such as a fresh-water bog is that an organism is tightly bound, and strict; an ecosystem is loosely bound, and lax.

In the long view, ecologies are temporary networks. Although some links become hardwired and nearly symbiotic, most species are promiscuous in evolutionary time, shacking up with a different partners as the partners themselves evolve.

In this light of evolutionary time, ecology can be seen as one long dress rehearsal. It's an identity workshop for biological forms. Species try out different roles with one another and explore partnerships. Over time, roles and performance are assimilated by an organism's genes. In poetic language, the gene is reluctant to assimilate into its code any interactions and functions directly based upon its neighbors' ways because the neighborhood can shift at any evolutionary moment. It pays to stay flexible, unattached, and uncommitted.

At the same time Clements was right. There is a basin of efficiency that, all things being equal, will draw down a certain mix of parts into a stable harmony. As a metaphor, consider the way rocks make their way to the valley floor. Not all rocks will land at the bottom; a particular rock may get stuck on a small hill somewhere. In the same way, stable intermediate less-than-climax mixtures of species can be found in places on the landscape. For extremely short periods of geological time -- hundreds of thousands of years -- ecosystems form an intimate troupe of players, who brook no interference and need no extras. These associations are far briefer than even the brief life of individual species, which typically flame-out after a million years or two.

Evolution requires a certain connectance among its participants to express its power; and so evolutionary dynamics exert themselves most forcefully in tightly coupled systems. In systems connected loosely, such as ecosystems, economic systems, and cultural systems, a less structured adaptation takes place. We know very little about the general dynamics of loosely coupled systems because this kind of distributed change is messy and infinitely indirect. Howard Pattee, an early cybernetician, defined hierarchical structure as a spectrum of connectance. He said, "To a Platonic mind, everything in the world is connected to everything else -- and perhaps it is. Everything is connected, but some things are more connected than others." Hierarchy for Pattee was the product of differential connectedness within one system. Members that were so loosely connected as to be "flat" would tend to form a separate organizational level distinct from areas where members were tightly connected. The range of connectance created a hierarchy.

In the most general terms, evolution is a tight web and ecology a loose one. Evolutionary change seems a strongly bound process very similar to mathematical computation, or even to thinking. In this way it is "cerebral." Ecological change, on the other hand, seems a weak-minded, circuitous process, centered in bodies shoved against wind, water, gravity, sunlight, and rock. "Community [ecological] attributes are more the product of environment than the product of evolutionary history," writes ecologist Robert Ricklefs. While evolution is governed by the straightforward flow of symbolic information issuing from the gene or computer chips, ecology is governed by the far less abstract, far more untidy complexity embodied by flesh.

Because evolution is such a symbolic process, we now can artificially create it and attempt to govern it. But because ecological change is so body bound, we cannot synthesize it well until we can more easily simulate bodies and richer artificial environments.