In a relatively primitive society, animals as well as humans will have to compete for food, territory, mating objects, and even wars between herds and tribes. So with lab rats living in a carefree place, what will ‘rat paradise’ be like?
Human society is increasingly developing, competing resources are not simply water, shelter or food but also minerals, oil, … and the scale of war also follows the historical flow. which is getting bigger and more dangerous. Furthermore, competing resources are intangible aspects, such as education, medical care, and work. The unequal distribution of these resources is often the focus of society in peacetime.
Everyone longs for a “paradise” free from disease, war, and oppression, although this paradise may not exist, but with the development of science, technology and society, we are getting closer. to heaven in the eyes of the ancients. We will also be curious about the future of human society. There are countless works trying to construct an impossibly beautiful perspective for exploring such issues, most of which of course have pessimistic results. In 1798, the British demographer and economist – Malthus showed in his thesis “Principle of Population” that the population increased exponentially but food production increased linearly. If things continued like this, it would reach a point where the population could no longer grow. The hidden content of this theory is that population growth does not necessarily bring prosperity, but can cause socioeconomic stagnation, hence the so-called “Malthusian trap”. After the end of World War II, the world gradually returned to prosperity, the United States ushered in a period of population explosion with a series of babies after the war, and with it, pessimistic views began to emerge. . Some people think that “overpopulation” can lead to a crisis, which in the short term will deplete resources for survival. This mentality of the majority of the population was immediately drawn to Malthus’ ideals. However, the success of the Green Revolution made Malthus’s model no longer valid, as food production spiked. However, the fear surrounding population explosion and its consequences still lingers here and there. Accordingly, a series of experiments demonstrating the effects of population explosion emerged. But a series of animal experiments seem to have yielded surprising results. Human estimates of resources for survival may still be too optimistic, but the real crisis coming from the population itself will seem obvious. The most prominent of which is the experiment of John B. Calhoun, an American expert specializing in the study of ethology and human behavior. 
John B. Calhoun and the Norwegian Rats. Calhoun was particularly interested in studying birds during his early years, and one of his studies was published in the journals of the Tennessee Bird Society at the age of 15. After that, Calhoun studied from bachelor’s degree to doctorate, and his research direction also gradually turned to animal behavior. Since his doctoral thesis was to study the 24-hour rhythm of the Norwegian rat, Calhoun’s work after graduation was also closely related to this rat. In 1947, Calhoun, then working at Johns Hopkins University, asked a neighbor to buy a piece of land less than 1,000 square meters to use as a laboratory. Then he decided to build an “artificial rat paradise” so that his rodents could live carefree. In the end, Calhoun named the place “Rat City”. 
With this amount of land, the area of the mouse city is not small, it is estimated that it can accommodate 5,000 rats, Calhoun also provides adequate food and water for his mouse subjects, while minimizing the maximum. the impact of disease and predators. Rats are only allowed to operate within the “city”. However, the development of the mouse city was not as smooth as imagined, even a bit bizarre. Calhoun initially included five pregnant female mice, but the reproductive rates of mice in this range were not as high as he had imagined. The number of rats in the study area never exceeded 200, and it stabilized at about 150, much smaller than the number of rats this “artificial paradise” could accommodate. Live rats cluster together in groups, and feed only at specific spots. This may have been the first experiment that brought Calhoun’s attention to population density. Five years after the failure of the rat city project, Calhoun joined the US National Department of Mental Health (NIMH) and was in a better position to design experiments on mice. At that time, Calhoun had a small team working with him, they improved the experimental environment on the mice as well as specially designed the breeding area so that the “artificial paradise” could work better. . The farming area is now only about 4.5 m long, 3 m wide, divided into 4 areas separated by electric fences, each area is equipped with unlimited food and water sources, there is also a multi-storey “apartment” that rats can enter in a spiral. The 4 areas separated by the grid are actually not completely isolated from each other, they are connected in pairs by 3 small bridges. Specifically, these four regions can be considered as four quadrants in the Cartesian coordinate system, where only a direct bridge exists that causes the path to move between the beginning – area 1 and the end – area 4 creating into a U shape. Calhoun designed a special feeding system, where solid food is kept behind nets and the collection process is not easy. 
In the first litter, but the residents here are reasonably arranged with a total of 32 mice, the number of males and females is equal and they are all adult rats that have reached reproductive age. According to the plan, the mice in the habitat would breed quickly, and the number would exceed the 40 limit for a short time, but Calhoun wouldn’t stop the experiment immediately. He would let the rats spawn to 80 and watch them. At first, the female rats were evenly distributed in the four regions, but when the fights between the males ended, the stronger males took over more females. Due to the design of four areas and three connecting bridges, a large number of low-status male rats will be concentrated in areas two and three, while the first and fourth areas become “swarms” of mice Males have higher status. At the bridge, the rats built their own barriers that prevented individuals from walking freely. Weak mice went to cages 2 and 3 to feed and could not return, only a small number of male rats remained in cages 1 and 4. 
At this point, the strange thing happened, the low-status male rat living in areas 1 and 4 – despite living among the females – had no desire to mate with the opposite sex. Instead they approached higher-status male rats, but the high-status males didn’t deny it either. The number of mice in the barn for 2-3 days is dense due to the continuous appearance of new litters of mice that “go and do not return”. At the same time, the rats’ eating behavior changed as they became accustomed to Calhoun’s feeding device. They refuse to eat alone, and only engage in net scavenging activities when and only in the presence of their own. The pressure from the population, from feeding (despite the abundance of food) creates a pattern that Calhoun calls a “behavioural sink”, roughly translated as “behavior alienation”; Rats begin to develop harmful behaviors. Under the influence of behavioral alienation, female rats have increased social interaction and decreased ability to care for offspring – and because young rats rely heavily on their mothers, herd numbers are at risk of decline. Whenever female mice move their nests, they often leave behind a large number of young mice. And yet, at the time of estrus, because female rats live in closed cages, they cannot escape from the males, and the brutal mating behavior in the cage affects the young even more. At one point, the mortality rate in the rat cage reached 96%. In dominant males, behavioral corruption causes them to become hysterical, frequently attacking their cagemates and even their young. 
In the vulnerable group of mice, Calhoun found traits that could separate mice into three distinct groups: The first type is called “pansexual”, they do not participate in competitions for social status, but will try to mate with any rat possible regardless of gender. or age. Not many individuals refuse this behavior. The latter, which Calhoun calls a “somnambulist”, is slow-moving, barely interacts with other rats, does not participate in social activities, and very few other individuals interact with them. ., but they are extremely fond of taking care of their appearance and are never violent. The third category, the group that most surprised Calhoun was named the “probes”. These are hyperactive individuals, constantly looking for opportunities to mate with rats of both sexes. Even if they were attacked by higher-status male rats, they would still frantically pursue females in heat. Once they reached the slums and found the young left behind, the fugitives found another source of nourishment. Continue: The end of the gruesome experiment, and the premise of the next one.
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