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Male Monkeys Show Neural and Hormonal Correlates of Jealousy

Research shows it's okay to say they feel jealousy when expected to do so.

A recent essay published in Frontiers in Ecology and Evolution by Nicole Maninger and her colleagues, "Imaging, Behavior and Endocrine Analysis of 'Jealousy' in a Monogamous Primate," caught my eye for two reasons. The first was the use of quotation marks around the word "jealousy" in the title and throughout the paper, and the second was the subjects of the research themselves, namely jealousy and the neural and hormonal correlates of this emotion. The entire essay is available online so here are a few snippets to whet your appetite for more.

Many animals appear to display jealousy but it has only been systematically studied in a few nonhuman animals. In an essay called "Dogs Know When They've Been Dissed, and Don't Like It a Bit," I reported on a very interesting study of jealousy in dogs that used the same methods that are used to study jealousy in young prelinguistic humans. All in all, the results of this study showed that dogs displayed jealousy (snapping, getting between their human and the object) when their humans showed affection to the stuffed dog, but not when they showed affection to nonsocial objects.

The new study in titi monkeys went a step further than other studies of jealousy by analyzing neural and hormonal changes in situations when male Coppery titi monkeys (Callicebus cuprous) were expected to show jealousy. These monkeys, who are socially monogamous and form strong pair bonds, display a preference for their mates and will guard them and don't like being separated from them. The researchers exposed eight captive-born male monkeys to two situations when they saw either their female partner next to a strange male, called the jealousy condition, or a strange female next to a strange male, called the control condition. They then used MRI and PET scanning to assess what was happening in the monkeys' brain and also analyzed hormonal changes. All of the details concerning behavioral and other measures are included in the online essay.1

As a result of their extremely detailed analyses, the researchers report:

After seeing his female pair mate next to a stranger male, male titi monkeys showed increased FDG [[18F]-fluorodeoxyglucose] uptake in the right lateral septum (LS), left posterior cingulate cortex (PCC) and left anterior cingulate (AC), and decreased uptake in the right medial amygdala (MeA) compared to the control condition. Our subjects also had higher plasma testosterone and cortisol concentrations and spent more time lip smacking in the jealousy condition compared to the control condition. In the jealousy condition, the amount of time looking at the pair mate next to a stranger male was associated with higher plasma cortisol concentrations. These neural and physiological changes may underpin the emotion of jealousy, which can act in a monogamous species to preserve the long-term integrity of the pair.

They also found lateralized effects of jealousy that also are seen in humans when displaying jealousy or in other situations of social exclusion.

All in all, this detailed study shows that it's okay to say these monkeys feel jealousy when they're expected to do so.

Why put scare quotes around the word "jealousy"? Different from doesn't mean less than

In concluding, the researchers write, "We also cannot say definitively that the subjects in our experiment experienced the emotion of 'jealousy.' Similarly, with humans we would need verbal confirmation that participants experienced this emotion." While some people are skeptical of using words such as jealousy, guilt, or embarrassment when they're talking about the emotional lives of nonhumans based on behavioral or observational data, they usually are convinced when neural and hormonal data also are provided, as these researchers have done.

These people prefer to put quotation marks (scare quotes) around words such as jealousy, guilt, love, grief, and sadness, for example, as these researchers have done when they talk about the emotional lives of other animals. This move suggests that perhaps they're not real—as if only we have true emotions but other animals don't—or because they're not like our own. Some skeptics also like to say they're "sort of" like ours but not as deep or as rich.

In the study of dogs I mentioned above, the same methods were used that are used to study jealousy in prelinguistic youngsters about whom inferences also have to be made about what they're feeling, and it's freely assumed that these youngsters are feeling jealousy even if they cannot confirm this verbally.

There's simply no reason to use scare quotes when talking or writing about animal emotions or to assume that their emotions aren't as real or as deep for them as our emotions are for us. Different from doesn't mean less than.

There's no doubt that many animals experience rich and deep emotions. Ample comparative data show that it's not a matter of if emotions have evolved in animals but why they have evolved as they have. We must never forget that our emotions are the gifts of our ancestors, our nonhuman animal kin. We have feelings and so too do other animals.

We also must not forget that it's important to use what we know on behalf of other animals with whom we interact, use, and abuse. Unfortunately, a "knowledge translation gap" still exists and what we know is not used on their behalf in far too many situations. Basically, the knowledge translation gap refers to the practice of ignoring tons of science showing that other animals are sentient beings and going ahead and causing intentional harm in human-oriented arenas. On the broad scale, it means that what we now know about animal cognition and emotion has not yet been translated into an evolution in human attitudes and practices (for more discussion please see "Animals Need More Freedom, Not Bigger Cages").

We need to keep the door open on the cognitive, emotional, and moral capacities of other animals. Numerous "surprises" are constantly being discovered. However, they're really not surprises when we realize how little we actually know about the cognitive and emotional capacities of a wide variety of nonhumans. Sometimes I feel it's surprising when other animals do not display certain behavior patterns or emotions, and I want to know more about the details of the studies that were conducted.

What makes the field of cognitive ethology—the study of animal minds—so exciting is that there is so much fascinating research to be done. Many studies open the door not only for more research on jealousy but also on other emotions such as guilt, shame, envy, and embarrassment, for example, for all of which there are many good stories and data from both citizen scientists and renowned researchers.

Please stay tuned for more on the fascinating cognitive, emotional, and moral lives of other animals.

1The researchers note, "All experimental procedures were approved by the Animal Care and Use Committee of the University of California, Davis, and complied with National Institutes of Health ethical guidelines as set forth in the Guide for Lab Animal Care."