One of the prominent areas of anthropology, primatology, studies nonhuman primates, their behavior, and social capabilities to provide valuable details about human evolution. Next, one of the primary traits that could characterize most apes, especially chimpanzees, is aggression among the male species. However, while aggression presents a significant component of social structure and gender differences among nonhuman primates, its role and influence in human evolution remain implicit. This essay will explore various manifestations of aggression among chimpanzees and bonobos, analyze and compare their causes, and determine whether aggression presents a significant component of human evolution.
One of the most developed representatives of the great apes’ group, also known as humans’ closes living relatives, the chimpanzees, are known for their intelligence. Chimps are rarely associated with aggressive behavior as they “lack the weapons” typically associated with violence, such as claws and string canines (Stanford, 2018). However, despite their high level of development, chimps also exhibit a very high amount of aggression to the point of lethal outcomes, even for the members of their own community. In fact, only a few animals besides humans are capable of such violent behavior. However, according to Preis and Jacob (2019), many chimps learned several strategies for avoiding aggressive behavior, such as cooperation and conflict management, because of the natural fear of injury. While most of the time, chimpanzees live in peace, several reasons could cause aggressive interactions.
The prominent reason for aggressive interaction among chimps is dominance relationships. Chimps are highly protective of their territories as territory size is closely connected to food resources. Food availability also presents one of the components of higher social status among chimps. According to Preis et al. (2019), a higher dominance level or social status is associated with many fitness benefits, such as better health, longevity of life, and even faster healing processes. The dominance and subordination ranks are reflected in levels of glucocorticoid hormones used to assess Hypothalamus-Pituitary-Adrenal (HPA) axis activity. The research conducted by Preis et al. (2019) suggests that urinary glucocorticoid levels are positively correlated with aggression rates, meaning that elevated aggression influences glucocorticoid levels. Another study by Preis and Jacob (2019) defined that status competition causes psychosocial stress on all-male species, even during periods of low rates of aggression, which was discovered through the analysis of urinary cortisol levels. Therefore, male chimps are stressed more during periods of high competition, while aggression arises mainly during periods of low competition because of social instability caused by food availability or mating.
Furthermore, considering that aggression in male chimpanzees is an outcome of adaptive strategy provides important context about human evolution. According to Stanford (2018), while violent behavior among chimps is considered immoral because of their connection with humans, in reality, aggression among chimpanzees’ is an amoral tool for obtaining more resources by eliminating competitors. Moreover, it was determined by Preis et al. (2019) that in cases with high risks of escalation, some chimps prefer avoiding aggression. Avoiding aggression and introducing different forms of behavior to show their competitiveness proves that chimps are capable of using adaptive strategies and elements of conflict management.
On the other hand, aggression is less common among bonobos, who are also considered close human relatives. Besides sharing physical differences with chimpanzees, bonobos have different social structure patterns, which influences conflict-resolving methods in bonobos. While bonobos, like chimpanzees, are also protective of their territory, bonobos have more complex inter-group relationships where they often meet to interact, which relates them to humans (Tokuyama et al., 2019). Even though bonobos tend to express aggression only to attack out-group individuals, they have never been seen killing other bonobos, compared to the level of aggression in chimps.
Moreover, there are considerable gender differences between female chimps and bonobos, as female bonobos have significantly higher social status. While there could be competition among male bonobos for social ranking, according to Tokuyama et al. (2019), mating is more influenced by the female mating partner’s choice and the social status of the male bonobo’s mother. Such a rational approach to mating differs from chimps, who frequently show aggression towards females. In turn, female chimps rarely show aggression towards male chimps, which is one factor that influences the overall level of aggression in chimps. According to King (2021), aggression in chimpanzees is shaped at a young age. Young chimpanzees become more aggressive when young chimps spend with protective mothers and time with aggressive males (King, 2021). A similar tendency is found in humans: suggesting that aggressive behavior is more acceptable for boys results in men being more physically aggressive. Therefore, the continuous dynamic of male chimps showing more aggression than female chimps reaffirms aggressive interactions among males.
Next, another significant environmental difference between bonobos that influenced their social structure and conditional gender equality is food availability. Higher social status and physical strength among chimpanzees suggest more available food resources. In addition, access to more food resources guarantees increased reproductive capabilities and success. On the other hand, Bonobos are less influenced by food availability as, according to Tokuyama et al. (2019), they exist in areas with an abundance of food resources with low seasonality. Therefore, the physical strength of bonobos plays a minor role as food is available in quantitates sufficient for several groups of bonobos, which results in relative equality of female and male bonobos. Moreover, as bonobo mothers often participate in competitions alongside their sons, female bonobos are not disregarded like chimpanzee females.
Lastly, there are two types of aggression defined in human evolution: proactive and reactive. Reactive aggression presents a reaction to provocation, while proactive aggression does not need provocation and focuses on constructing a plan in which the victim will have minimal opportunities to fight back (Wrangham, 2019a). In general, humans are believed to be more like chimps, as they exhibit a proactive type of reaction, but humans also tend to be less reactive than chimps, making them more like bonobos. It could be that a reduced level of reactive aggression in humans occurred through human evolution and self-domestication.
Comparing and analyzing the sources of aggression among chimpanzees and bonobos revealed that environmental factors, such as food availability, determined key differences of social structure and aggression patterns in chimps and bonobos. Therefore, from the point of human evolution, aggression patterns in people could be connected to environmental factors and the availability of recourses. People historically tend to show more intense proactive aggression in fighting and starting wars for resources. This essay analyzed why proactive aggression in chimps and humans has similar reasons and provided an outlook on what human evolution would look like if there were plenty of resources available for the humankind.