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I view the species Homo sapiens with a gimlet eye, as I think I have already made clear. This is in spite of the fact that I harbor an immense fondness for some few individual specimens of that species. It seems clear to me, based upon the information currently available, that the species Homo sapiens is the most voracious and rapacious species that has ever trod the face of this little planet. Homo sapiens not only display an intra-species viciousness, but also direct their viciousness at other species inhabiting the planet. There is good evidence that there have been other periods of great extinctions in the past. The great extinction of species currently underway, however, is for the first time directly attributable to the conduct of one of those same species--the supposedly self-aware one--Homo sapiens.
How is one to make sense of this? For my part whenever I encounter some further example of the cruelty of our species, particularly the thoughtless, untoward behavior of some of our species toward others of our own species, I have tended to invoke the nostrum that there are “too many rats in the cage.” The human population of the planet is after all hurtling toward 9 billion, an unimaginable number. While there remain vast stretches of inhospitable, formidable landscapes on the planet that are sparsely inhabited, specimens of our species tend to huddle thickly together in relatively small, friendlier areas.
After some years of casually tossing off that explanation “too many rats in the cage,” I determined to look further into the science underlying it. I am an Enlightenment kind of guy after all. That brought me around to the work of ethologist John B. Calhoun, the man who actually put the rats, and sometimes mice, in those cages and watched and reported. I fully recognize the pitfalls of extrapolating from the behavior of rats and mice to explanations of human behavior, but one can hardly help oneself. The manner in which Professor Calhoun wrote up his observations does not discourage that either. Perhaps he is to be criticized for that.
I found that Professor Calhoun conducted a whole series of such experiments, each of different design, some involving rats and some involving mice. For our purposes here, I shall give a brief description of two general types, the rat thing and the mouse thing, as well as the results as I understand them.
His early experiments in the late 1950’s involved domesticated Norway rats. He constructed a large cage in a barn with three or four “rooms” between which the rats could travel freely. Unlimited food and water. No predators. No disease. A rat “utopia.” He initially stocked the cage with a number of rats for which there was ample space. First, he noticed that even though there was ample food and water in all of the “rooms,” the rats tended to crowd together in one of the rooms where they ate together leaving the other “rooms” largely unoccupied. (This might perhaps explain why all of our great restaurants are in urban areas and require reservations.) Thus, overpopulation developed in one room while the other rooms were mainly empty.
Then, as the population increased, as populations will, he noticed changes in the little rat society. The female rats began having difficulty carrying their pregnancies to term. There was increased maternal mortality among those who did. The mothers who survived giving birth paid little or no attention to their motherly duties. As for the males, they become hyperactive, extremely aggressive, cannibalistic, and pathologically withdrawn. They also displayed “sexually deviation,” in Professor Calhoun’s words, a subject that I shall leave untouched here for good reason, one rat's "sexual deviation" being another rat's delight, I say. There was a societal breakdown as a result of what the good professor called “behavioral sink,” which then led to the extinction of the rat population.
Briefly, the mice experiments in the 1960’s can be described this way. In this case Professor Calhoun introduced four pairs of mice into a nine foot square pen complete with nesting boxes, food, and water. The only limiting factor on their reproduction was that space, but a space with nesting boxes sufficient to accommodate 3,840 mice. Initially, the population increased apace reaching 620, but then the population increase started to slow. The mouse society began to break down with the mice displaying the same aberrant behavior to that of those Norway rats. A female mouse successfully gave birth on day 600, which was the last successful birth in the colony. The population at that point stood at 2,200 mice. The society had totally broken down at that point what with the aberrant behavior, however, and the colony began its descent into extinction.
As I was contemplating the implication of all that, I encountered a newspaper column by a writer whom I admire, Leonard Pitts, Jr. It occurred to me that if it is fair to extrapolate from rodent behavior to human behavior, then it is equally fair to extrapolate from human behavior to rodent behavior. It is entirely possible that Professor Calhoun simply happened to put rats and mice in those cages that did not like each other.