At this point some of you may be wondering what it is exactly that makes the process of captive chimpanzee group formation so difficult, so I thought we could take a step back and look at some of the challenges.
It starts with biology. Free-living chimpanzees live in large communities ranging from just over a dozen to nearly two hundred individuals. The dynamic structure of these communities, a system known as fission-fusion, allows for regular changes in group size and composition in response to factors such as the abundance of food or the presence of females in estrus. This form of social organization enables chimpanzee communities to adapt to variations in resource availability by temporarily splitting into smaller parties while retaining the protection and other benefits of living in a large group.
But while subgroups are free to split off from and later rejoin the community, only certain individuals are generally allowed to leave their community entirely to join another. To do this successfully, it helps to be young and female.
Chimpanzee communities as a whole are understandably protective of what is most important to their survival and reproductive success; namely, access to food and potential mates. Neighboring communities threaten to compete for these scarce resources, which is why chimpanzees often exhibit such fierce territoriality. Groups of males, and in rare cases both males and females, will coordinate patrols of their territorial boundaries and attack, often lethally, lone individuals or small groups from neighboring communities that have wandered too close.
As Anthony mentioned previously, males remain in their natal groups for life and form lifelong bonds with one another. Consequently, there is no biological or cultural mechanism to facilitate the transfer of males from one community to another. Nor is there a straightforward path for adult females to transfer. But as adolescent females reach sexual maturity, they generally leave their natal communities and seek out new one. This instinctual emigration is assumed to be an evolved mechanism to prevent inbreeding within the community and the timing of their departure is anything but arbitrary. While fear of outsiders remains the general rule, males are typically welcoming of young immigrant females, especially ones who arrive with estrus swellings. Resident females are not always as welcoming to the newcomers who, bear in mind, will be eating from the same fruit trees and potentially competing for the attention of resident males, but the newcomers can rely on protection from the resident males as they assimilate into the new community.
So there is a clear pattern, with limited exceptions, across nearly all chimpanzee communities in Africa: There is only one reliable ticket to move between communities, and it is determined by the immutable characteristics of age and sex and to a large extent reliant on the selfish desires of the males who hold power. When we form groups in captivity, we are almost always fighting against millions of years of natural history.
Of course, chimpanzees are not products of instinct alone, but beneath the layers of culture there remain a number of instinctual tendencies that stand out in the captive environment. An example: When captive chimpanzees go to bed at night, they typically make nests just like their wild cousins. These nests may be made out of straw, wood wool, or blankets instead of branches, but they generally share one trait in particular with those of their wild counterparts: they have high sides to hold them in. For wild chimpanzees, the nest serves as a cradle to keep them from plunging dozens of feet to the ground while they slumber. Perhaps it would only make sense for captive chimpanzees to do the same, except that they create the same doughnut-shaped nests even when sleeping in the middle of a concrete floor. In fact, sometimes they sleep directly on the concrete with all of the blankets arranged into a ring around them. It’s a bit of security-seeking encoded in the biology of a species far removed from the environment in which they evolved. Instincts can be attenuated by both learning and the environment but they remain a powerful driving force in our behavior.
To some extent, the nurture side of the nature-nurture influence probably does mitigate some of these xenophobic tendencies. Lab-reared chimpanzees are regularly moved between pairs or small groups throughout their lives, and they do not grow up in a culture that systematically reinforces their biological predispositions towards outsiders as their wild counterparts do. In a way, captive-born chimpanzees are trained to ignore their biology. Sadly, their upbringing presents its own set of problems.
Maintaining peace and order in a chimpanzee community requires strict adherence to certain social norms and conventions. If you watch the video of Burrito and Willy B meeting alone for the first time, you can see the delicate communication required to navigate such a perilous moment. To facilitate the encounter, Willy B covers his top teeth with his upper lip and shows only his lower ones. This signals an intent not to harm – specifically, not to bite – much in the same way that a dog’s bow signals an intent to play. At the same time, he engages in vigorous “breathy panting,” a vocalization that conveys friendliness and interest. He senses Burrito’s fear and as a result he gives Burrito a wide berth. Burrito, for his part, conveys to Willy B that despite his fear he would like to get closer by extending an arm toward him. One misstep by either party and the entire process could unravel into outright aggression, as it did during their group encounter two weeks prior.
And while they overcame the risks of this initial encounter, the challenge of actually living together has, unfortunately, only begun. Sustaining friendships and alliances is difficult and constant work, and studies show that chimpanzees separated from their mothers at an early age and raised by humans exhibit social deficiencies that make group living harder as adults. These chimpanzees fail to develop the knowledge and skills required to navigate the complex and often subtle rules of chimpanzee social life. As a result, they are more likely to have to live in small groups or in some cases, alone.
Despite all of this, most chimpanzees in sanctuaries, zoos, and laboratories can and do live in groups. As they should, because the benefits of a large social network are immeasurable. But we need to keep in mind what we are asking of them: to plunge ahead, ill-equipped and unprepared, and with almost no control at all, into a process that goes against their very instincts. This is one of the many sad realities of captivity for chimpanzees.
So despite our setback with the group of ten, I am, at the moment, hopeful. Burrito and Willy B have been living together since Wednesday, grooming regularly and playing with one another on occasion. These two guys overcame their fears and are experiencing the initial whispers of a bond that should have been their birthright as male chimpanzees. Whether it will be sustained over time, and amidst the turbulent influence of other group members, remains to be seen. But it’s a promising start.
