Using findings from 23 studies focused on what psychologists refer to as “inequity aversion,” researchers analyzed data from over 60,000 observations of 18 different animal species. This research is considered the “largest empirical investigation of non-human inequity aversion so far,” in which the team reexamined data analyses and introduced a new metric to enhance the fairness concept.
A question that has intrigued thinkers for centuries is: Are humans the only ones who seek fairness and feel frustration when others receive what we desire?
In recent times, evolutionary psychologists have proposed that humans may not be as unique as we think. Various animals, including corvids and capuchin monkeys, appear to exhibit feelings akin to jealousy, especially when they are denied a preferred treat. Many believe this serves as evidence that we share this aversion to unfairness with other species.
However, recent findings from researchers at the University of California, Berkeley suggest that humans may actually be distinct in this regard.
The team, analyzing 23 studies on “inequity aversion,” explored over 60,000 observations across 18 animal species. They claim this to be the “largest empirical investigation of non-human inequity aversion conducted to date,” incorporating a new analytical approach that broadens the understanding of fairness.
“This data does not support the idea that animals experience jealousy,” explained Oded Ritov, a fourth-year Ph.D. student in UC Berkeley’s Psychology Department. “If any effect exists, it is rather weak and likely appears only in specific situations.”
“However, it’s not comparable to the deep-seated sense of fairness that we observe in humans.”
The findings were published on November 27 in the journal Proceedings of the Royal Society B.
As the principal author of the paper, Ritov examines how human behaviors have developed, the extent to which they are inherent to our advanced brains, and what is shaped through intricate cultural experiences. He also studies non-human animals to gain insights into what makes our species unique.
Our inherent sense of fairness in resource distribution likely played a crucial role in our ability to create shelters, share food, and form complex societies. It’s important to recognize that humans have varied interpretations of fairness. However, at the core is a psychological phenomenon known as “inequity aversion,” which embodies a reluctance toward unequal resource distribution and beliefs about how things should be shared.
The concept of inequity aversion is familiar to many, especially parents and siblings of young children. If one child receives a better gift than another, the response often involves emotional outbursts. It’s not solely about the child lacking a toy; it’s also about someone else receiving something desirable, indicating aversion to inequality.
The extent to which this understanding of fairness differs for non-human animals has long been debated.
A significant study by primatologist Frans de Waal, which included a widely-shared video of a capuchin monkey reacting negatively when denied a grape, illustrated that certain animals may possess a grasp of inequity aversion similar to that of human children. The scenario showed that while both monkeys were content with cucumber slices, the one receiving a grape expressed discontent with the unequal treatment by refusing to eat its cucumber and protesting loudly.
De Waal and colleagues argued that such responses support the view that humans are not alone in their sense of justice. Similar findings have been reported in studies involving corvids, dogs, and mice, indicating a form of inequity aversion in these species as well.
However, Ritov cautions that this interpretation might be “simple, and possibly anthropomorphic.” Yet, it’s not the only explanation.
He pointed out that many of these studies face issues stemming from a replication crisis that has affected psychology and other fields. While findings can be intriguing, they often rely on small sample sizes and are not easily replicated, which clouds their broader impact in science.
“We believed it would be beneficial to consolidate as much data as possible regarding this question and identify potential patterns within a larger dataset,” Ritov stated.
The results from the updated analyses with a new variable suggest that the observed reactions among animals may not truly reflect jealousy. Instead, they seemed disappointed based on prior expectations of receiving a grape, as indicated by previous research behaviors. Subsequent experiments similarly provoked discontent in monkeys even when grapes were visible in an empty cage where no other monkeys were present.
“We believe these rejections represent a form of social protest,” Ritov remarked. “However, it appears the animals are not protesting due to a relative lack compared to another but rather are expressing dissatisfaction that they are not treated as well as they could be by humans.”
Perhaps the animals’ reactions have less to do with inequity aversion and more with unmet expectations—a sentiment both humans and non-humans can undoubtedly relate to.
