The behavioral sink is a term coined by American behavioral researcher John B. Calhoun, referring to an abrupt population collapse in extremely mild environments. Calhoun conducted a series of experiments with mice and rats which are called mice/rats utopia or paradise, some of which resulted in such population collapses.
Calhoun's explanation for the outcome of his experiments was that overpopulation leads to social hierarchies where there was more demand for social roles than could be reasonably filled. He claimed the ensuing physiological strain this harsh competition for limited social roles put on the mice subjected to these conditions resulted in the emergence of "autistic-like creatures, capable only of the most simple behaviours compatible with physiological survival", eventually leading to the "breakdown of all normal social behavior", with this often resulting in the auto-extinction of the rodent colonies in question.
Behavioral sinks in Calhoun's experiments are thought to have been caused by evolutionary mismatches caused by overpopulation or the relaxation of natural selection in these 'utopian' conditions inevitably leading to the build-up of deleterious mutations among the mice that ultimately had the effect of reducing both group and individual fitness (see social epistasis amplification model).
Description of the experiments[edit | edit source]
In Calhoun's experiments, rodent populations were kept in artificial, small environments with otherwise ideal conditions and unlimited food supply. In one of his experiments which was later once reproduced, the animals abruptly reproduced less and showed unhealthy social behavior after 1.7 years of rapid population growth. This was primarily caused by male animals failing to claim territories of significant size, thus failing to claim dominance status and thus constantly engaging in fights. Some managed to follow the females into their burrows, eschewing the typical courtship rituals rodents engage in (intermittently poking their heads into the female's burrow until she accepts his advances). They often found neglected and dead young lying in the nests, which they frequently cannibalized.
Non-secluded Dropouts[edit | edit source]
Those dubbed "dropouts", who had ceased doing any sort of useful social activity, but remained in the center, engaged in frequent "pointless violence".
Probers[edit | edit source]
Some rodentcels alternatively became hypersexual, and either engaged in homosexual behaviors or incessantly chased female rodents in estrous (dubbed probers by Calhoun), in spite of being defeated and chased away by the dominant rodents.
Beautiful ones[edit | edit source]
Those male and female mice lucky enough to secure long-term non-crowded territory were guarded in "apartments" with small entrances. Aggressive territorial males guarded the entrances to the "apartments". Within these apartments were what Calhoun deemed the "beautiful ones", or those who engaged in only grooming, sleeping, and eating. They lost social functioning, and did not have sex. They also did not care for their young.
Harems[edit | edit source]
The few dominant rodents that remained, monopolized almost all breeding opportunities with the remaining females, maintaining harems by chasing away any lesser male who attempted to approach their territory, apart from a few subordinate males, who never attempted to mount the females in the dominant rodent's harem, and were therefore permitted to approach. In some end pens, where dominant rodents maintained harems, the female rodents often exhibited healthy nurturing behaviors, feeding, nesting and protecting their young from harm. Calhoun stated that this was due to the estrous females in such pens being protected from incessant and unwanted attention from the lower status males, particularly the hypersexual "probers" who obsessively stalked and approached any estrous female they could find, despite being repeatedly defeated and driven away by the dominant rodents. These "brood pens", exhibited the highest infant survival rate.
Gangs[edit | edit source]
Population decline[edit | edit source]
With the lack of territory normally established by males, the females also reproduced less, neglected their offspring and cared for their offspring on their own, partly overtaking male tasks of maintaining territory and demonstrating aggression.
Conclusion[edit | edit source]
The experiments that resulted in such a behavioral sink ended in the extinction of the colony, due to all males and females having become uninterested in reproduction. However, the behavioral sink was not the outcome of all experiments, e.g. when food was supplied in a manner where it could be consumed in a way that did not tend to incite male competition.
Criticism[edit | edit source]
There is dispute about the degree to which the experiment has similarities to pathological behavior in dense human populations, with Calhoun being strongly criticized during his lifetime and afterwards for inferences regarding human social behavior and the effects of overpopulation he drew from his experiments. There were at least two partial replications of the experiments, Kessler (1966) managed to achieve a concurrently high and stable population in his two similar experiments. But there were some similarities in the deviant behavior (such as homosexuality and cannibalism) that was exhibited by the mice in Kessler's experiments, though there was a general continuance of reproductive activity among the mice in both experiments. Hammock (1971) also noted extensive behavioral pathology in his experiment with a difference strain of mice, though there was no population decline or collapse, nor were there any "beautiful ones" (though some mice did engage in excessive grooming behavior) or cases of dominant males forming and maintaining harems. This suggested a innate biological mechanism that auto-regulated population growth among the mice in Hammock's experiment.
Calhoun has also been criticized for failing to take in account any other explanations of the behavioral sink phenomena, such as disease pandemics leading to population decline or dysgenic breeding (such as inbreeding depression) among the mice leading to ultimately fatal mutational load among the mice, causing them to become so mutated and autistic they could no longer reproduce or engage in functional social behavior. It has been suggested the negative social consequences of deleterious mutations multiply in feedback loops (social epistasis amplification).
References[edit | edit source]