Aristotle would probably flunk a college ecology class. With tutoring he might overcome the language gap, and even learn how to file his homework by computer. But he'd be doomed to failure for his firm belief in a balance of nature.
Most ecologists do not like the idea -- still popular more than two millennia after it gained acceptance -- that nature is in balance. Mention the concept and some researchers get downright dyspeptic. A Wheaton College professor named John Kricher has even written a book, "The Balance of Nature: Ecology's Enduring Myth." "Historically, the notion of a balance of nature is part observational, part metaphysical, and not scientific in any way," he argues, leaving no chance for disagreement: "Any notion of a balance of nature is surely naïve, given the reality of present climate change and its collective effect on global ecosystems."
Why are ecologists such as Kricher so touchy about whether nature is in balance? In a word: Creationism. While Aristotle was by no means a Christian fundamentalist, fundamentalism (and indeed all Christianity) owes much to him for laying the intellectual framework for teleology with his so-called Great Chain of Being. The balance of nature was born out of the conviction that every creature had a proper place in the world, a permanent role embodying the purpose for which it was created. Kricher provides an example of this worldview in the ancient observation that predators have lower fecundity than prey, a divine ordering ensuring that the former have enough to eat without eradicating the latter. It's a clever explanation, fatally flawed scientifically by the lack of proof for a divine ordering.
Instead we have evolution, inarguably one of the most powerful theories ever advanced. Evolution needs no creator, for the creative act is built into the system, which applies natural selection to random genetic mutation. While the Great Chain of Being is perfectly conceived and eternally lasting, constant change is the creative engine of evolution, and progressive compromise is its product. "One obvious argument against the existence of a balance of nature, at least as such a balance implies purpose and teleology, is the reality of just plain luck," Kricher writes. "If evolution-altering events are stochastic in nature, then patterns of extinction and speciation … may have little to do with anything other than 'dumb luck.' This reality does not reduce the importance of natural selection. Indeed, natural selection is stimulated in such situations, as it is in such situations that new species evolve." We are indebted to imbalances for the environmental pressures that led to everything from multicellular organisms to human intelligence.
All of this is known by most people with a high school education, and (at least outside the Creationist community) it's as uncontroversial as the Earth's revolution around the sun. The question is whether the dismissal of intelligent design rules out the possibility of balance in nature. This issue is far from trivial, for precisely the reasons Kricher cites: the reality of present climate change and the necessity to do something about its collective effect on global ecosystems. In his rambling way, Kricher makes a fine case for precisely the position he proposes to overturn. As he acknowledges, "the balance of nature is esthetically satisfying, a fact that is largely responsible for its continued vigor through the ages." He also recognizes that "environmental ethics must embrace emotive connections." If the idea of nature in balance is broadly appealing to us, should that view not be encouraged as our collective environmental irresponsibility threatens the future of the planet?
Current ecological data, much of it cited by Kricher in the tedious manner of an Ecology 101 lecture, scientifically supports the notion of balance in nature at least as strongly as it refutes the idea. For instance, consider research on the sea otter, which Kricher describes at great length, only rather obviously to conclude that "humans can unwittingly induce major alterations in ecosystem food webs."
In fact, the research illustrates much more than that. Between 1990 and 1997, in the western Aleutian Islands, the otter population plummeted by 90 percent because orcas began feeding on them. Previously orcas subsisted on fish-eating harbor seals and sea lions, but human over-fishing in the region led to a drop in seal and sea lion populations, forcing orcas to broaden their diet. Since the otters preyed on sea urchins, fewer otters meant more urchins, a rapidly expanding population that decimated the undersea kelp forests on which they fed. The loss of kelp in turn further disturbed the fish in the area, which relied on kelp for shelter, exacerbating the seal and sea lion famine, impelling orcas to eat more otters. The effect was so dramatic because otters were a "keystone" species in the region, meaning that the stability of the food web depended disproportionately on their well-being. Which is to say that a steady otter population helped to maintain the balance of nature.
Crucially, all of this was specific to the western Aleutian Islands in the late 20th century. Otters are not always a keystone species, and there's nothing universal or immutable about this particular island ecosystem. Indeed, the western Aleutians may have changed so dramatically because of the otter crisis that otters may no longer play a significant environmental role. Another entirely different balance may have been attained since the study was conducted in 1998, a balance which will inevitably be overturned in its own right. In other words, the point is not about otters but about food webs, which are significant because -- often in ways too complex to be described -- they represent natural balances. They're inherently dynamic, but mechanisms such as cascades and feedback loops balance the energy flow to a far greater extent than could be expected by purely random arrangement.
Anybody with a basic understanding of ecology knows this, yet the importance of it is no more to be dismissed than the importance of change. A model of the natural world in successive states of balance is as valid as a model of the natural world in successive fits of imbalance. A model is a man-made thing, and its value is pragmatically determined. Looking at the natural world from the perspective of imbalance may be more useful for describing the creative work of evolution, but viewing the natural world from the perspective of balance is often better for purposes of figuring out how ecosystems -- from marshes to rainforests -- operate in a given place and time, and how least to disturb them. The model of nature in balance is also likely to be more effective for purposes of persuading people that global warming is real, and perilous from a human perspective, and even that it can be moderated by habitat conservation or decreasing fuel consumption.
At the deepest level, life thrives in a balance between natural imbalance and balance. Kricher himself describes this in writing about the importance of natural disturbances to an ecosystem, from cold snaps to meteor strikes. "What ecologists have learned is that intermediate disturbance levels seem to result in maximum biodiversity. Too little disturbance and the competition among species will eliminate some species and reduce the diversity. Too much disturbance and few species will be able to tolerate the frequency of perturbations." Through the agency of global warming, human environmental irresponsibility is exponentially increasing disturbance levels, upsetting the balance between balance and imbalance.
Thinking about nature in terms of balance does not mean placing our future in the hands of a Creator, but rather considering our behavior in terms of the model pragmatically needed now. There is an aesthetic side to it -- just as there was an aesthetic side to the work of John Muir -- but the aesthetics is not replacing good science, merely allying good science with forceful emotion. If we envision nature in terms of balance, we're more likely to balance the carbon budget. And we may even survive as a species long enough to enjoy the balance of nature, as Aristotle once did, for its own intrinsic beauty.