The rise in human population continues to exert enormous strain on earth’s ecosystems and finite resources. Scientific American recently devoted an issue to one solution among many needed to solve this worrisome situation. The cover reads, “We have seen a brighter future, and it is urban.” People living in dense urban environments “typically have smaller energy footprints, require less infrastructure and consume less of the world’s resources per capita.” But, what is the cost? There are always tradeoffs. Alla Katsnelson, from Scientific American, notes that city dwellers suffer “higher rates of mental illnesses, including anxiety disorders and schizophrenia” than their rural counterparts. All the factors underlying this difference are not known or well understood, but some of the possible causes appear to stem from the fact that urban environments are nothing like the ancestral environments from which our sensory systems evolved. As our hunter-gather ancestors learned during the Agriculture Revolution, our biology does not take kindly to rapid upheavals in cultural evolution. In a way, their experience somewhat parallels the one we face today. Put simply, the Industrial Revolution and the subsequent urbanization has been to our sensory systems what the agriculture revolution was to our digestive system.
Around 10,000 years ago groups of hunter-gathers began primitive farming. This shift almost single-handedly changed the course of human history, but our digestive system did not make it easy. Farming “produces 10 to 100 times more calories per acre than foraging.” In lieu of this fact, “from 10,000 BC to AD 1, the world population increased approximately a hundredfold.” Of course, similar to today, the quantity of food rarely related to its quality. Early farmers began eating foods foreign, in type and/or amount, to their hunter-gather ancestors. The first farmers ate less fresh meat and more plants but with less variety. “The carbohydrate fraction of their diet almost tripled, while the amount of protein tanked. Protein quality decreased as well, since plant foods contained an undesirable mix of amino acids, the chemical building blocks of which proteins are made.” The limited set of harvested plants and scarcity of fresh meat caused vitamin shortages rarely experienced by hunter-gathers. These shortages contributed to diseases such as beri-beri, pellagra, rickets, and scurvy. The average height of humans who adopted farming dropped by almost five inches, and the poor diet can partly explain the increase in infant mortality among early farmers.
Obviously, farming did impart many advantages. If not we would still be hunter-gathers. The sheer quantity of people, regardless of health, created a qualitative advantage all its own. Jared Diamond writes, “a larger area or population means more potential inventors, more competing societies, more innovations available to adopt—and more pressure to adopt and retain innovations, because societies failing to do will be eliminated by competing societies.”
Similarly, the Industrial Revolution fundamentally changed our way of life. Prior to the Industrial Revolution we spent the majority of our lives outdoors. Our forefathers were more likely to be farmers than any other profession, which meant they needed an intimate knowledge of the natural environment including weather, pests, animal lifecycles, and soil. The great migration to the city during the Industrial Revolution ended all of that.  Today we spend “upward of 95 percent of our time sealed away from anything remotely like” the ancestral environments our sensory systems were forged in. Our sensory diet now contains large portions of contemporary materials such as concrete, glass, steel, and plastics. Beyond the chemicals these materials emit, which have been implicated in Sick Building Syndrome, these materials might not have the sensory signatures we need for healthy development. Perhaps this is partly why urbanites exhibit higher rates of mental illness.
For instance, Professor Roger Ulrich found that patients recovering from a cholecystectomy fared far better if they were assigned to a room with a view of nature (trees) than one that looked out on a brick wall. Likewise, a study of two architecturally identical 16-story Chicago public housing buildings showed that the residents living in the building surrounded by vegetation more effectively coped with stress, better managed conflicts, and had higher cognitive functioning than those living in the vegetatively challenged building.  More recently, a survey of 11,000 people found that those who lived within 1 km of green space reported lower levels of stress than those that lived farther away. Also, those who were more likely to actually visit a green space were the least likely to report stress. Although this study only used interviews and questionnaires to gather data, other studies measuring physiological changes suggest these findings are more than just perceived levels of stress. For example, a study recorded the performance, blood pressure, and emotional state of people who had either walked in an urban setting or a natural setting. Those walking in the natural settings experienced an increase in positive affect, decrease in anger, performed better on an attentional test, and exhibited lower diastolic blood pressure indicating less stress. These studies most likely do not tell the whole story behind the differences in mental illness, but they do suggest that the current urban environment does not provide the right type and/or amount of stimulation we need for healthy mental development (for other likely causes see note).
So, it is possible to be environmentally friendly, but not human friendly. Professor Stephen Kellert believes a prime example of this is the LEED Platinum Donald Bren School of Environmental Science and Management building at UC Santa Barbara. In his book Building for Life, Kellert writes “this [85,000-square-foot building] is among the nation’s best examples of low environmental impact architecture, having succeeded in reducing various adverse effects on the natural environment,” but “Much of the building lacks a positive connection to the natural environment and remains aesthetically impoverished.” It completely ignores our evolutionary past, and what constitutes healthy and needed stimulation. If all buildings were built to this standard the environment would be better for it, but our mental well-being might unnecessarily suffer.
There is reason, however, to be optimistic. If the Agricultural Revolution is an appropriate analogy to draw on then we might imagine a future where the differences in mental illness have faded away. The first farmers eventually overcame their nutritional deficiencies by cultivating a wider range of crops, adopting new methods of food preparation, and in a few fortuitous cases undergoing biological evolution, i.e. lactose tolerance beyond the age of four. They suffered tremendously during the transition, but that doesn’t have to be our story. We are unlike the first crop charmers in one distinct and sizable way; we have the advantage of knowing why they became so unhealthy. We have the opportunity to learn from our past and build a material culture based on science. Collaborating with the fields of biology and anthropology, architects now have the ability to develop healthy material pallets that capitalize on contemporary materials’ strengths without causing the needless suffering the early farmers faced with an unbalanced diet.
If you enjoyed this article check out more by Christopher N. Henry here.
 Bettencourt, Luis M.A. and Geoffrey B. West. “Bigger Cities do More with Less,” Scientific American. September 2011, p 52-53.
 Katsnelson, Alla. “The Stress of Crowds,” Scientific American. September 2011, p. 18.
Also see, Peen J, Schoevers RA, Beekman AT, Dekker J. “The current status of urban-rural difference psychiatric disorders,” ACTA Psychiatrica Scandinavica 2010, 121 p. 84-93.
Lederbogen, Florian; Peter Kirsch, Leila Haddad, Fabian Streit, Heike Tost, Philipp Schuch, Stefan Wust, Jens C. Pruessner, Marcella Rietschel, Michael Deuschle and Andreas Meyer-Lindenberg. “City living and urban upbringing affect neural social stress processing in humans,” Nature 2011 474 p. 498-501.
Kringlen, Einar; Sven Torgersen, Victoria Cramer. “Mental illness in a rural area. A Norwegian psychiatric epidemiological study,” Social Psychiatry and Psychiatric Epidemiology. 2006, 41 p. 713-719.
 Cochran, Gregory; Henry Harpending. The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. Basic Books, New York 2009 p. 67-84.
Different groups of hunter-gathers and early farmers had different diets with different proportions so this explanation makes this complex subject fairly simplistic. For starters see:
Perry, George H.; Nathaniel J. Dominy, Katrina G. Claw, Arthur S. Lee, Heike Fiegler, Richard Redon, John Werner, Fernando A. Villanea, Joanna L. Mountain, Rajeev Misra, Nigel P. Carter, Charles Lee, and Anne C. Stone. “Diet and the evolution of human amylase gene copy number variation,” Nature Genetics. V. 39(10) 2007 p. 1256-1260.
Kolber, Elizabeth. “Flesh of Your Flesh” The New Yorker, November 9, 2009.
Marlowe, Frank W. “Hunter-Gathers and Human Evolution,” Evolutionary Anthropology. 14 2005 p. 54-67.
Diamond, Jared. Guns, Germs, and Steel: The Fates of Human Societies. New York, Norton 2005.
 Diamond, Jared. Guns, Germs, and Steel: The Fates of Human Societies. New York, Norton 2005, p. 407.
 Baker, Nick. “Human Nature” in Environmental Diversity in Architecture. Edited by Koen Steemers, and Mary Ann Steane. New York, Spon Press, 2004 p. 48.
 Orr, David and Robert Michael Pyle. “The Extinction of Natural Experience in the Built Environment.” In Biophilic Design, edited by Stephen R. Kellert, Judith H. Heerwagen, and Martin L. Mador, Hoboken, New Jersey, John Wiley & Sons, 2008 p. 214.
For amount of time spent indoors see Klepeis, Neil E., William C. Nelson, Wayne R. Ott, John P. Robinson, Andy M. Tsang, Paul Switzer, Joseph V. Behar, Stephen C. Hern, and William H. Engelmann. “The National Human Activity Pattern Survey (NHAPS): a resource for assessing exposure to pollutants,” Journal of Exposure Analysis and Environmental Epidemiology 2001 Volume 11, p 231-252.
 For Symptoms of Sick Building Syndrome see, Godish, Thad. Sick Buildings: Definition, Diagnosis and Mitigation. London, Lewis Publishers, 1994 p. 2.
 Ulrich, Roger. “Biophilic Theory and Research for Healthcare Design.” In Biophilic Design, edited by Stephen R. Kellert, Judith H. Heerwagen, and Martin L. Mador,. Hoboken, New Jersey, John Wiley & Sons, 2008 p. 94.
 Taylor, Faber, Frances Kuo, and William Sullivan, “Growing up in the inner city: Green spaces as places to grow,” 24.
 Stigsdotter, Urika K., Ola Ekholm, Jasper Schipperijn, Mette Toftager, Finn Kamper-Jorgensen & Thomas B. Randrup. “Health promoting outdoor environments – Associations between green space, and health, health-related quality of life and stress based on a Danish national representative survey,” Scandinavian Journal of Public Health. 2010; 38: 411-417.
 Hartig, Terry, Gary W. Evans, Larry D. Jamner, Deborah S. Davis, Tommy Gärling. “Tracking restoration in natural and urban field settings,” Journal of Environmental Psychology 23, 109-123, (2003).
 The idea that sensory differences between the urban and rural environments cause the differences mental illnesses is only one among many possible hypothesizes. A decent summary of other possible causes can be found at http://www.patient.co.uk/doctor/Poverty-and-Mental-Health.htm
- Studies have shown higher risk of mental disorder among persons living in urban versus rural areas.Epidemiological research has documented that associations between particular features of the urban environment, such as concentrated disadvantage, residential segregation and social norms, contribute to the risk of mental illness. Some studies have suggested a link between urban environmental factors and a higher risk of mental illness, particularly schizophrenia.
- As ever, there is the question as to whether this is causation (urbanity causing psychosis) rather than selection (high-risk individuals move into urban areas, often as part of the social drift accompanied by onset of illness). Some consider the effect of the urban environment to be conditional on genetic risk (a gene-environment interaction).
- There are important within-city variations in the incidence of schizophrenia associated with different neighbourhood social characteristics. For example, the incidence of non-affective psychoses varies widely across South East London and this is not adequately explained by looking at individual-level risks. The cause of these neighbourhood variations is unknown but may be a reflection of social fragmentation.”
The website provides a few sources if you would like to explore the veracity of these claims. With these in mind, it is highly unlikely that sensory differences are the only source of mental anguish. Consequently, we also do not know how large of a role sensory differences play. It easily could be a minor.
 Kellert, Stephen R. Building for Life: Desiging and Understanding the Human-Nature Connection. Washington DC: Island Press 2005 p. 98-100.
 Cochran, Gregory, Henry Harpending. The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. Basic Books, New York 2009. For lactose tolerance see, Ingram, Catherine J.E., Charlotte A. Mulcare, Yuval Itan, Mark G. Thomas, Dallas M. Swallow. “Lactose digestion and the evolutionary genetics of lactase persistence,” Human Genetics. 2009,124 p. 579-591.