Overcrowding was a big concern for 20th-century prophets of population doom. In 1962, National Institute of Mental Health researcher John Calhoun published an influential article, "Population Density and Social Pathology," in Scientific American. Calhoun had conducted experiments in which he monitored overcrowded rats. As population density increased, female rats became less able to carry pregnancies to full term—and they so neglected the pups that were born that most died. Calhoun also documented increasing behavioral disturbances among the male rats, ranging "from sexual deviation to cannibalism and from frenetic overactivity to a pathological withdrawal." All of these pathologies amounted to a "behavioral sink" in which infant mortality ran as high as 96 percent and populations sank toward extinction.
Calhoun's work was cited both by professional researchers and by overpopulation popularizers. American Public Health Association President Larry Gordon, for example, asserted in 1982 that "too many members of the human species are already being destroyed by violence in overpopulated areas in the same manner as suggested by laboratory research utilizing other animals." Explicitly referencing Calhoun's behavioral sink in his 1968 book, The Pump House Gang, hipster journalist Tom Wolfe riffed: "Overcrowding gets the adrenalin going, and the adrenalin gets them hyped up. And here they are, hyped up, turning bilious, nephritic, queer, autistic, sadistic, barren, batty, sloppy, hot-in-the-pants, chancred-on-the-flankers, leering, puling, numb…"
But now, in stark contrast to these visions of chaos and collapse, new research suggests that increased population density isn't a disaster at all. Indeed, it's channeling human efforts and aspirations in productive directions.