Is It Only Natural for Us to Be Jealous?

What we've learned about the evolution of a potentially dangerous emotion.

Posted Sep 22, 2014

Psychologist Dr. Christine Harris and her colleague, Caroline Prouvost, recently published the results of a study confirming what many of us already suspected: Dogs get jealous. They demonstrated this by evaluating how dogs responded to their owners petting a fake dog and a jack-o-lantern pail, or reading from a pop-up book complete with melodies. The dogs were least reactive to their owners reading a book out loud; a little less than half wanted their owners to ignore the pail; but a whopping 78% actively attempted to disrupt their owner’s friendly behavior towards a toy puppy by pushing or touching the owner. Some dogs went so far as to get in between the fake puppy and their owner, while others downright snapped at the offending "dog."

(One dog out of 36 seemed to have “issues” and snapped at the book and pail as well. Yikes.)

This is an interesting study for what it tells us about dogs alone, but it has broader implications for what jealousy is all about: Since it appears that we share this trait with other species, does that mean jealousy is natural? If so, what does this mean when considering jealous feelings in our own lives and relationships?

To answer these questions, let’s examine jealousy a bit more closely: Jealousy is frequently considered as a secondary emotion, triggered in response to primary emotion like fear or anger. It's the feeling that someone is trying to take something you have. If you are a French angelfish or a titi monkey, someone might be trying to steal your mate. And how exactly does a male titi monkey display his jealousy? He increases his aggression—first vocally, then physically—in direct proportion to the proximity of an outsider. The closer another male gets to his mate, the more distressed he becomes.

Given that a titi monkey couple forms a tight pair-bond and rely heavily on each other to raise their children, each has a lot to lose if their mate is filched by another. This is not unusual. Frankly, anytime a strong bond is formed with a member of the opposite sex, or same sex, jealous behavior will emerge when an interloper is detected. In that sense, we can think about how jealousy may have evolved to protect our social bonds from trespassers.

In species that don’t form strong romantic attachments, jealousy behavior over mates isn’t as frequent. Squirrel monkeys, for example, don’t really seem to care one way or the other, so jealousy over mates is a non-issue. Food, however, is another matter—jealous behavior over the allocation of material resources is probably the next most-common scenario in which we see jealousy emerge. Sibling rivalry, anyone?

If you think about it, as soon as you have a sibling, your parents’ time, energy, affection, and resources is divided up into smaller and smaller bits. Not to mention, just as in some human families, in many other species there is some version of parents allocating resources differently among the kids. Yes, animal moms and dads can play favorites, too—hence, all the jealousy. In birds, one way parents do this is by allocating hormones differentially during development, the end result being that one chick may be born larger and have a leg up on its siblings. A far more common strategy is for one sibling (usually the larger one) to just get rid of the competition. (This is where we can all breathe a collective sigh of relief that we are human and not pelicans, eagles, or sand sharks.)

Whether it is time, affection, resources, or mates, we can see that, in other animals, jealous behavior is functional and purposeful. This brings up a critical difference between humans and other animals: Other animals respond to actual threats from potential mate thieves and to real differences in the allocation of time, affection, and resources. What we don’t see is jealousy in response to imaginary threats. A titi monkey will not wake up, having dreamed that their partner was unfaithful, and behave aggressively toward an imaginary intruder, or worse, its own mate.

In a sense, one could say that other animals are better at assessing situations and having an accurate view of what is happening around them. Animals are very busy accomplishing a lot of goals: They have to find food, survive, raise offspring, defend their territory, and maintain social relationships. They literally do not have the time to devote to unproductive activities not founded in their immediate reality—not to mention, picking fights unnecessarily is extremely risky. Someone could get injured.

We humans not only have the tendency to become jealous over imagined threats, we also don’t often seem to take into account the “cost” of certain behaviors. Spending your time watching, following, or checking up on a partner takes time away from accomplishing your own goals.

A healthy dose of suspicion seems understandable, whether in humans or mountain baboons. What doesn’t make sense is the all-consuming perception of constant threat. This is costly to one’s self and damaging to one's relationship—a fact which becomes obvious when we recognize that jealousy often emerges as the third-leading motive of non-accidental homicide.

That’s not to say not to say that we should ignore signs that our relationships may be in danger. However, it pays to be a bit more like a titi monkey and evaluate whether something is actually happening or whether it’s just insecurity wreaking havoc—not unlike that one hypersensitive dog who snapped at the pail. Speaking of which, the dogs clearly perceived the toy dog as a real threat, and reacted appropriately: Most of them first "checked" by sniffing the rear end of the toy dog and, after getting a good whiff, only three decided they had nothing to worry about.