Coping with CROWDING by Frans B
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POPULATION GROWTH has been thought, since the time of Thomas Malthus, to produce dire consequences such as disease, scarcity and social deviancy. This dark view seemed confirmed by rodent studies. Yet little evi- dence suggests that people are similarly affected: we seem to handle large crowds quite well for the most part. Coping with CROWDING by Frans B. M. de Waal, Filippo Aureli and Peter G. Judge 76 Scientific American May 2000 Coping with Crowding Copyright 2000 Scientific American, Inc. n 1962 this magazine published a seminal But, one could argue, perhaps such a re- paper by experimental psychologist John lation is obscured by variation in national IB. Calhoun entitled “Population Density income level, political organization or some and Social Pathology.” The article opened other variable. Apparently not, at least for dramatically with an observation by the late- income. We divided the nations into three 18th-century English demographer Thomas categories—free-market, former East Block Malthus that human population growth is and Third World—and did the analysis automatically followed by increased vice and again. This time we did find one significant misery. Calhoun went on to note that al- correlation, but it was in the other direc- though we know overpopulation causes dis- tion: it showed more violent crime in the ease and food shortage, we understand virtu- least crowded countries of the former East ally nothing about its behavioral impact. Block. A similar trend existed for free-mar- This reflection had inspired Calhoun to ket nations, among which the U.S. had by conduct a nightmarish experiment. He placed far the highest homicide rate despite its low an expanding rat population in a crammed overall population density. The Nether- room and observed that the rats soon set lands had a population density 13 times as about killing, sexually assaulting and, even- high, but its homicide rate was eight times tually, cannibalizing one another. Much of lower. this activity happened among the occupants Knowing that crime is generally more of a central feeding section. Despite the common in urban areas than it is in the presence of food elsewhere in the room, the countryside, we factored in the proportion rats were irresistibly drawn to the social of each nation’s population that lives in stimulation—even though many of them large cities and controlled for it. But this could not reach the central food dispensers. correction did nothing to bring about a This pathological togetherness, as Calhoun positive correlation between population described it, as well as the attendant chaos density and homicide. Perhaps because of and behavioral deviancy, led him to coin the the overriding effects of history and culture, phrase “behavioral sink.” the link between available space and hu- In no time, popularizers were comparing man aggression—if it exists at all—is decid- politically motivated street riots to rat packs, edly not clear-cut. inner cities to behavioral sinks and urban Even if we look at small-scale human ex- areas to zoos. Warning that society was periments, we find no supporting evidence. heading for either anarchy or dictatorship, Crowding of children and college students, Robert Ardrey, an American science jour- for instance, sometimes produced irritation nalist, remarked in 1970 on the voluntary and mild aggression, but in general, people nature of human crowding: “Just as Cal- seemed adept at avoiding conflict. Andrew S. houn’s rats freely chose to eat in the middle Baum and his co-workers in the psychiatry pens, we freely enter the city.” Calhoun’s department at the Uniformed Services Uni- views soon became a central tenet of the vo- versity found that dormitory residents who luminous literature on aggression. shared facilities with many people spent less In extrapolating from rodents to people, time socializing and kept the doors to their however, these thinkers and writers were rooms closed more often than did students making a gigantic leap of faith. A look at who had more space. Baum concluded that human populations suggests why such a the effects of crowding are not nearly as simple extrapolation is so problematic. overwhelming as originally presumed. Pub- Compare, for instance, per capita murder lished in the 1980s, these and other findings rates with the number of people per square began to undermine, at least in the scientific —as we did, ck kilometer in different nations community, the idea that people and rats re- o using data from the United Nations’s 1996 act in the same ways to being packed to- estst W Demographic Yearbook. If things were gether. In modern society, people commonly straightforward, the two ought to vary in assemble in large masses—during their daily ETERSON tandem. Instead there is no statistically commute to work or during holiday-season BRIAN P meaningful relation. shopping expeditions—and most of the time A persistent and popular view holds that high population density inevitably leads to violence. This myth, which is based on rat research, applies neither to us nor to other primates Coping with Crowding Scientific American May 2000 77 Copyright 2000 Scientific American, Inc. 3 MALES Aggression 2 Grooming 1 0 Low Medium High Density 3 FEMALES Incidents per Hour 2 AAL W DE Grooming M. 1 ANS B Aggression FR RHESUS MONKEYS from three different settings show different rates of grooming— that is, of calming one another. The monkeys seem to adapt to crowded conditions by 0 grooming more frequently. Among the males, grooming of each other and of females was Low Medium High more common when they lived in crowded conditions than when they lived in more spa- AN CHRISTIE Y cious quarters. Among female nonkin, aggression was common and increased further with Density BR crowding but was accompanied by increased grooming, which served to reduce conflicts. SOURCE: Peter G. Judge and Frans B. M. de Waal they control their behavior extraordi- population density seemed to increase wide range of species—from macaques narily well. aggression occasionally—but the oppo- to chimpanzees—as well as strict and Calhoun’s model, we must conclude, site was also true. One report, for in- well-defined hierarchies that remained does not generally apply to human be- stance, described intense fighting and stable for decades. This view of an of- havior. Is this because our culture and killing when a group of macaques were ten anxiety-filled existence was con- intelligence make us unique, or is the released into a corral 73 times larger firmed when researchers found high management of crowding part of an than their previous quarters had been. levels of the stress hormone cortisol in older heritage? To answer this question, Then, after two and a half years in the the blood of wild monkeys [see “Stress we turn to the primates. corral, a similar increase in aggression in the Wild,” by Robert M. Sapolsky; occurred when the monkeys were Scientific American, January 1990]. Primates Are Not Rats crowded back into a small pen. As the view of primates became more Whereas the macaque study manipu- complex, and as the rat scenario was rimate research initially appeared to lated population density through envi- weakened by counterexamples, re- Psupport the harrowing scenario that ronmental change, other early research searchers began to wonder whether pri- had been presented for rats. In the did so by adding new monkeys to exist- mates had developed a means to reduce 1960s scientists reported that city- ing groups. Given the xenophobic nature conflict in crowded situations. We saw dwelling monkeys in India were more of monkeys, these tests mainly measured the first hint of this possibility in a study aggressive than were those living in their hostile attitude toward strangers, of the world’s largest zoo colony of chim- forests. Others claimed that monkeys in which is quite different from the effect panzees in Arnhem, the Netherlands. zoos were excessively violent. Those of density. The better controlled the stud- The apes lived on a spacious, forested monkeys were apparently ruled by terri- ies became, the less clear-cut the picture island in the summer but were packed fying bullies who dominated a social hi- turned out to be. Increased population together in a heated building during the erarchy that was considered an artifact density led to increased aggression in winter. Despite a 20-fold reduction in of captivity—in other words, in the only 11 of the 17 best-designed studies space, aggression increased only slightly. wild, peace and egalitarianism pre- of the past few decades. In fact, the effect of crowding was not vailed. Borrowing from the hyperbole In the meantime, the view of wild pri- entirely negative: friendly grooming and of popularizers, one study of crowding mates was changing. They were no greetings, such as kissing and submis- in small captive groups of baboons even longer the purely peaceful, egalitarian sive bowing, increased as well. went so far as to report a “ghetto riot.” creatures people had presumed them to We wondered if this conciliatory be- As research progressed, however, con- be. In the 1970s field-workers began re- havior mitigated tension and proposed flicting evidence accumulated. Higher porting sporadic but lethal violence in a a way to test this possibility. Without ig- 78 Scientific American May 2000 Coping with Crowding Copyright 2000 Scientific American, Inc. noring the fact that crowding increases behavior varied in discernible ways. We one matriline also fiercely support one the potential for conflict, we predicted collected detailed data on 122 individ- another in fights against other matri- that primates employ counterstrategies— ual rhesus monkeys at three different lines. Because of their strict hierarchy including avoiding potential aggressors sites in the U.S.: in relatively cramped and pugnacious temperament, rhesus and offering appeasement or reassuring outdoor pens at the Wisconsin primate seemed to be ideal subjects.