As a scientist, I find that only one vision of the city really gets my hackles up-the notion that a city is somehow “unnatural.” a blemish on the face of nature.</p>
<p>The argument goes like this: Cities remove human beings from their natural place in the world. They are a manifestation of the urge to conquer nature rather than to live in harmony with it. Therefore, we should abandon both our cities and our technologies and return to an earlier, happier state of existence, one that presumably would include many fewer human beings than now inhabit our planet.</p>
<p>There is an important hidden assumption behind this attitude, one that needs to be brought out and examined if only because it is so widely held today. This is the assumption that nature, left to itself. will had a state of equilibrium (a “balance of nature”) and that the correct role for humanity is to find a way to fit into that balance. lf you think this way, you are likely to feel that all of human history since the Industrial (if not the Agricultural)Revolution represents a wrong turning-a blind alley something like the failed Soviet experiment in central planning. Cities, and particularly the explosive postwar growth of suburbs (“urban sprawl”) are agencies that destroy the balance of nature, and hence are evil presences on the planet.</p>
<p>What bothers me about this point of view is that it implies that human beings, in some deep sense, are not part of nature. “Nature,” to
[line 28] many environmental thinkers, is what happens when there are no people around. As soon as we show up and start building towns and cities, “nature” stops and something infinitely less worthwhile starts. lt seems to me that we should begin our discussion of cities by recognizing that they aren’t unnatural, any more than beaver dams or anthills are unnatural. Beavers, ants, and human beings are all part of the web of life that exists on our planet. As part of their survival strategy, they alter their environments and build shelters. There is nothing “unnatural” about this.</p>
<p>Nor is there anything unnatural about downtown areas. Yes, in the town the soil has been almost completely covered by concrete, buildings, and asphalt: often there is no grass or undisturbed soil to be seen anywhere. But this isn’t really unnatural. There are plenty of places in nature where there is no soil at all -think of cliffsides in the mountains or along the ocean. From our point of view, the building of Manhattan simply amounted to the exchange of a forest for a cliffside ecosystem</p>
<p>Look at the energy sources of the downtown ecosystem. There is, of course, sunlight to provide warmth. ln addition, there is a large amount of human-made detritus that can serve as food for animals: hamburger buns, apple cores, and partially filled soft drink containers. All of these can and do serve as food sources. Indeed, urban yellow jackets seem to find sugar-rich soft drink cans an excellent source of “nectar” for their honey–just notice them swarming around waste containers during the summer.</p>
<p>A glimpse of downtown, in fact, illustrates that the city can be thought of as a natural system on at least three different levels. At the most obvious level, although we don’t normally think in these terms, a city is an ecosystem, much as a salt marsh or a forest is. A city operates in pretty much the same way as any other ecosystem, with its own peculiar collection of flora and fauna. This way of looking at cities has recently received the ultimate academic, accolade-the creation of a subfield of science, called"urban ecology," devoted to understanding it.</p>
<p>At a somewhat deeper level, a natural ecosystem like a forest is a powerful metaphor to aid in understanding how cities work. Both systems grow and evolve, and both require a larger environment to supply them with materials and to act as a receptacle for waste. Both require energy` from outside sources to keep them functioning, and both have a life cycle-birth, maturity, and death.</p>
<p>Finally, our cities are like every other natural system in that, at bottom, they operate according to a few well-defined laws of nature. There is, for example, a limit to how high a tree cart grow, set by several factors including the kinds of forces that exist between atoms in wood. There is also a limit to how high a wood (or stone or steel) building can be built-a limit that is influenced by thosesame interatomic forces.
So let me state this explicitly: A city is a natural system, and we can study in the same way we study other natural systems and how they got to be the way they are.