From David Abram's The Spell of the Sensuous, this quotation reminds us that
evolution has shaped humans in ways that may not be irnmedi- ately evident.
Forest, Savanna, City: Evolutionary Landscapes and Human Functioning William C. Sullivp
The careful study of perceptual experience unexpectedly began to make evident the hidden centrality of the earth in all human experience. -David Abrarn, The Spell of the Sensuous (1996) From David Abram's The Spell of the Sensuous, this quotation reminds us that evolution has shaped humans in ways that may not be irnmediately evident. Indeed, growing evidence shows that through evolution, the earth shaped not only our perceptions but also our very nature (Pinker 2002). To a striking degree, human nanire includes being strongly attracted to places that include trees and other natural features. What are the consequences of living in places that have no resemblance to the landscapes that supported our evolution? Do humans today experience certain costs by living mostly disconnected from all traces of the natural world? I explore these questions building on my work and that of my colleagues in the Human-Environment Research Laboratory at the University of Illinois. I begin by examining the habitats that supported human evolution and the notion that all animals seek particular habitats that enhance their functioning and reproduction. This examination generates three specific questions about the impact of living in barren urban settings that are answered by a series of recent studies. This chapter concludes by considering the implications for design and management of our current habitats and for human attachments to urban places.
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Human Habitats What were the characteristics of the habitats that supported human evolution? The answer depends on what period of human evolution is under consideration. During the past 10 million years, the earth has undergone extreme, repetitive shifts in climate, plant, and animal life (Potts 1996). The dramatic, repetitive alteration of the surface of the earth grew from an interaction between earth's orbit and geology. Dramatic climate change resulted not only from oscillations in earth's orbit of the sun (ranging in scale from 20,000 to 100,000 years), but also from volcanic outpourings, convulsions in the terrain, and a repetitive freezing and thawing of the polar ice caps. It was in this highly unpredictable environment that human intelligence, language, and creativity emerged. Let us take a closer look at how the surface of Africa changed over rime. Five million years. ago, or roughly 250,000 generations ago, our ancestors lived in an.enormous tropical forest.' It was in this forest that our evolutionary break from chimpanzees occurred and in which our fully upright, bipedal ancestors (Australopithecus afarensis) emerged some 185,000 generations ago. The famous "Lucy" was a member of this group. Roughly 100,000 generations ago, a period of global cooling driven by polar glaciations fragmented the vast tropical forest of Africa into a patchy mosaic of forest interspersed with grassland (Burenhult 1993). The fragmentation of the forest and the introduction of large, grassy areas put pressure on many species to adapt to these new conditions (Megarry 1995). It was out of this landscape that the first members of the genus Homo-Homo habilis-evolved roughly 90,000 generations ago. H.habilis, or handy man, as they are commonly known, retained tree-climbing adaptations such as curved finger bones (Megarry 1995). From H. habilis and a landscape that was more forest than grassland, we jump forward to approximately 45,000 generations ago when H. erectus flourished in east Africa. H erectus faced considerable challenges from another peak of glacial activity brought on by global cooling that resulted in harsh conditions and seasonal variation in climate and thus availability of food (Walker and Shipman 1996). The cooling also broke
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up the tropical landscape into even patchier areas, which by now were dominated by savanna and interspersed with forest. This process of punctuated change in the landscape of our evolution occurred again during another great ice age-beginning about 5,700 generations ago (115,000 years ago), just after the first anatomically modem humans (Homo sapiens) had emerged (Foley 1995; 'Groves 1993). The result of 100,000 years of global cooling was what we now think of as the typical East African savanna--grassland dotted with clumps of trees (Burenhult 1993). Behaviorally modern humans, who emerged from this landscape roughly 2,000 generations ago, lived as nomadic huntergatherers in small bands of a few dozen people. -Inbut the blink of an eye in geological time, the next sigdcant landscape changes occurred. But this time the changes were not due to the repercussions of global climate change; they occurred due to human activity. Around 250 generations ago (5,000 years ago), half the world's population had access to agriculture and thus a more stable, predictable supply of food, fiber, and medicine. Since the dawn of agriculture, the pace of change in the human habitat has accelerated. B e g h i & a mere 11generations ago, the Industrial Revolution brought the advent of large cities and, for much of the world's human population, the beginning of a profound shift away from the intimate, daily contact with other species that had characterized human existence for millennia. This trend has been reinforced recently with the advent of the computer revolution, a transition that began only a generation ago. My point here is obvious: we humans have spent 99 percent of our time on earth living in tremendously close contact with forests, grasslands, and other intact ecosystems. Indeed, until recently, each of our ancestors participated in what can be called from today's perspective a life-long camping trip (Orians 1986). A life-long camping trip stands in stark contrast to the amount of nature that many modern humans experience. With our center cities often devoid of green space or even street trees and new suburban developments that dot the countryside on what was recently corn or bean fields, too many Americans live today without the hint of the savanna or forest. Are there costs to living so far removed from the landscape of our evolution?
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Forest, Savanna, City
Habitat Selection To begin to address this question, it is helpful to consider the scholarship on habitat 'selection. Biologists have shown that all organisms capable of moving on their own will seek specific habitats. Although seagulls can fly, they do not fly everywhere. Rather; they search for particular enviro~tentalconditions that support their functioning. The same is true of dolphins, bees, and every other animal. Biologists call this general phenomenon habitat selection-the process by which animals find settings that support a significant pan of their life cycle, if not their entire life. Because habitat selection powerfully influences survival and reproductive success, the mechanisms involved in choosing a habitat have been under strong selection pressure for millennia (Orians 1986). According to the basic biological argument uqderlying habitat selection theory, natural selection has favored individuals who were motivkted ia explore and settle in environments likely to afford the necessities of life and to avoid environments with poorer resources or that pose higher risks (Orians 1980, 1986; Orians and Heerwagen 1992). The brain mechanisms involved in habitat selection were shaped by natural selection because individuals who -sought out supportive environments produced, on the average, more progeny than did individuals who were indifferent to such concerns. There is compelling evidence that it is not simply their reproductive success that suffers when animals occupy unfit habitats. When cats, for instance, are placed in unfit habitats, they become antisocial and a great deal more aggressive. They stop playing, and there is continuous hissing, growling, and fighting (Leyhausen 1965). For rats, the social impacts of being in an unfit habitat are even more pronounced. Wilson catalogues the consequences as including "hypertension, . .cannibalism, and atypical and nonfunctional nest construction, with infant mortality rising to 96%" (1975:255). Thus, the evidence suggests that unfit habitats lead to unhealthy patterns of behavior and functioning in which social and psychological breakdowns occur. This analysis leads us to our main question: If humans are adapted to the savanna, forest, and a close connection to the natural world, do we show social and psychological impacts or even breakdowns when we live
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with very little nature? Several studies conducted by the scientists at the Human-Environment Research Lab shed light on this question. Our research measured various dimensions of social and psychological func- + tioning, while holding constant the broad cultural impact on daily life. Our studies do not intend to deny the importance of culture in shapingb urban life; the learned patterns of social interaction and meaning with regard to nature are important. We seek to explore, however; whether patterns can be seen within one cultural context when contact with the surrounding natural world is varied. The Neighborhoods When we set out to study the effect of green neighborhood landscapes on individuals and communities, we faced a major challenge: selecting neighborhoods that would allow us to make comparisons between individuals with more or less contact with green landscapes (Sullivan and Kuo 2000). Ideally, we wanted neighborhoods that met four criteria. First, the neighborhoods must have variation in the amount of green cover-from places that were full of plants to places that were barren. Second, besides the amount of vegetation, other environmental and cultural features should be held constant within the neighborhood. Third, residents should be randomly assigned to the areas that had more or less green cover. And finally, the residents should have no influence over the maintenance of the vegetation near their home. We found two public housing developments in Chicago that met these criteria: Robert Taylor Homes and Ida B. Wells. Each development has pockets of trees and grass and expanses of barren territory (figure 10.1). Each is strikingly consistent in its architecture and because of their neighborhood scale, residents reported no building-wide or neighborhoodwide patterns of cultural variation. At the time of our studies, Robert Taylor Homes consisted of 28 identical 16-story apartment buildings laid out in a single file line along a 3-mile corridor. Each building at Robert Taylor Homes is bordered on the west by an interstate highway and railroad tracks and on the east by a six-lane municipal thoroughfare and wide sidewalk. Ida B. Wells included 124 low-rise (two- to four-story) . apartment buildings laid out on a typical grid pattern2 Because of its
