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Where does diversity come from? In 1983, microbiologist Julian Adams discovered a clue when he brewed up a soup of cloned E. coli bacteria. He purified the broth until he had a perfectly homogenized pool of identical creatures. He put this soup of clones into a specially constructed chemostat that provided a uniform environment for them -- every E. coli bug had the same temperature and nutrient bath. Then he let the soup of identical bugs replicate and ferment. At the end of 400 generations, the E. coli bacteria had bred new strains of itself with slightly different genes. Out of a starting point in a constant featureless environment, life spontaneously diversified.

A surprised Adams dissected the genes of the variants (they weren't new species) to find out what happened. One of the original bugs had undergone a mutation that caused it to excrete acetate, an organic chemical. A second bug experienced a mutation that allowed it to make use of the acetate excreted from the first. Suddenly a symbiotic codependence of acetate maker and acetate eater had emerged from the uniformity, and the pool diverged into an ecology.

Although uniformity can yield diversity, variance does better. If the Earth were as smooth as a shiny ball bearing -- a perfect spherical chemostat spread evenly with uniform climate and homogeneous soils -- then the diversity of ecological communities on it would be far reduced from what it is now. In a constant environment, all variation and all diversity must be driven by internal forces. The only constraints on life would be other coevolutionary life.

If evolution had its way, with no interference from geographical and geological dynamics -- that is, without the clumsiness of a body -- then mindlike evolution would feed upon itself and breed heavily recursive relationships. On a globe without mountains or storms or unexpected droughts, evolution would wind life into a ever-tightening web of coevolution, a smooth world stuffed with parasites, parasites upon parasites (hyperparasites), mimics, and symbionts, all caught up in accelerating codependence. But each species would be so tightly coupled with the others that it would be difficult to distinguish where the identity of one began and the other left off. Eventually evolution on a ball-bearing planet would mold everything into a single, massive, ultradistributed planetwide superorganism.

Creatures born in the rugged environments of arctic climes must deal with the unpredictable variations that nature is always throwing at them. Freezing at night, baking during the day, ice storms after spring thaw, all create a rugged habitat. Habitats in the tropics and in the very deep sea are relatively "smooth" because of their constant temperature, rainfall, lightfall, and nutrients. Thus the smoothness of tropical or benthic environments allows species there to relinquish the need to adapt in physiological ways and allows them room to adapt in purely biological ways. In these steady habitats we should expect to see many instances of weird symbiotic and parasitic relationships -- parasites preying upon parasites, males living inside of females, and creatures mimicking and mirroring other creatures -- and that's what we do find.

Without a rugged environment life can only play off itself. It will still produce variation and novelty. But far more diversity can be manufactured in natural and artificial worlds by setting creatures in a rugged and vastly differentiated environment.

This lesson has not been lost on the wannabe gods trying to create lifelike behavior in computer worlds. When self-replicating and self-mutating computer viruses are loosed into a computer memory uniformly distributed with processing resources, the computer viruses quickly evolve a host of wildly recursive varieties including parasites, hyperparasites, and hyper-hyperparasites. David Ackley, one computer life researcher, told me, "I finally figured out that the way to get wonderfully lifelike behavior is not to try to make a really complex creature, but to make a wonderfully rich environment for a simple creature."