What is jealousy? If we want to explain jealousy, which is widespread in humans, but also in many animal species, we must refer to some empirical studies that have been conducted by evolutionary psychology. Without this perspective, it would be very difficult to find explanations on a topic like this that has many social, experiential, psychological, relational, and more important implications, although the main one is of course sexual. The protagonists, at the moment when jealousy is raised, must be three (the two partners and a third person), not two, otherwise, it would no longer be jealousy, but mutual envy (Aaron, 1990), a feeling that can still be just as devastating. Jealousy arises then when doubts arise about mutual fidelity and, in case there are no excesses, it becomes functional to the stability of the couple.

Jealousy has always existed, but the tools to bring it into action today have changed, sometimes even institutionalised. At one time, the unfaithful wife was, at best, removed from the family, at worst, publicly stoned to death (the Taliban in Afghanistan applied it until 2001, so in Nigeria and beyond). Today this does not happen anymore, but jealousy can manifest itself through other means, no less violent than those of the past, for example, through the phone or mobile phone or by sending anonymous letters. We are talking about stalking, which can have very serious psychological repercussions on victims, even with suicide, otherwise a murder. When jealousy is triggered by a strong and sometimes unfounded belief in the infidelity of the partner, it can lead to frenzy (Othello syndrome, as the experts call it). This last form of jealousy is mainly found in Italian melodrama. One example for all is Verdi's Othello, taken from a work by William Shakespeare, in which the ensign Jago hates Othello because he promoted Cassio to Captain, not him as he expected, so he wants revenge for it. He does so by telling Othello that he heard Cassio say love sentences to his wife Desdemona. Othello falls to deception, first stabs Desdemona to death, and then, with the same dagger, kills himself. In the works of Verdi, there are many tragic endings of this kind, but also in others where he kills himself for treason, such as Cavalleria Rusticana by Mascagni and I Pagliacci by Leoncavallo. In both works, jealousy is disruptive because hatred for the rival is involved.


Charles Darwin in The Expression of the Emotions in Man and Animals (1872) said that jealousy is a complex state of mind and that the only way to detect it is through the eyes of the person hiding it, the green-eyed monster, based on an expression of Shakespeare. Darwin, basically, wanted to suggest that all emotions, including jealousy, should be considered biological phenomena, or rather, genetic predispositions. In fact, they are perceptual elaborations of physiological activity (arousal) raised by environmental stimuli. In essence, it is a defensive measure of a partner to get out of a threatening situation. In essence, without the slightest form of jealousy, a couple would have no sense of existing, unless there are constraints of another kind, for example, economic dependence.

Jealousy, within certain limits, not in excesses, would have the task of restoring the partners' psychological, emotional, and physiological balance. The nervous centres involved in the realization of homeostatic balance are mainly the hypothalamus, thalamus, hippocampus, and cingulate gyrus, which process information useful for the control of emotions, but also jealousy.

Jealousy, however, is inexpressive. It is not recognized through the facial expressions that are typical of the American psychologist Paul Ekman (1971): that is, anger, disgust, fear, sadness, happiness, and surprise, which are universal and should, therefore, apply to all cultures. Then, contempt, pride, and others were added, but not jealousy. Why is jealousy not considered an emotion? Because, in fact, it is a feeling, rather than real emotion. It is the evaluation of an emotional state, so it is neither immediate nor unconscious, but slow, linear, and conscious.

Evolutionary psychology

Jealousy, both in humans and animals, has the fundamental function of leading partners towards reproductive success. In most cases, two young people get together, love each other to have children sooner or later.

Male jealousy is different from female jealousy. In fact, male jealousy, unleashed by infidelity or presumed infidelity, can manifest itself with the estrangement of the partner from the possibility of having extramarital relations, up to sexual violence, physical and psychological mistreatment which is sometimes more serious than physical. A study conducted by David Buss (2000) shows that, for example, a man's emotional infidelity, for his wife or partner, is much more serious than purely sexual infidelity, whereas the opposite is true for a woman. Women fear their partner falling in love with another woman more than the fact that he has had casual relationships with different women and therefore it is difficult for them to be emotionally involved. However, it is not uncommon for sex to also involve the emotional sphere. According to Buss, it is mainly women, more than men, who get involved in an emotional relationship after the more materially sexual one, although there can always be exceptions.

That this is true can be demonstrated by the fact that in all cultures, from the East to South and North America, passing through Europe, the perception of betrayal takes on the same universal nuances. Man is reluctant to forgive sexual infidelity, especially when the rival is in a prominent social position, i.e. he is richer, more powerful, and endowed with greater economic resources; for the woman, the youth, beauty, and attractiveness of the rival are more important.


Jealousy is adaptive and innate. We find it everywhere, albeit with gender differences. In order to understand why in front of the betrayal the masculine and feminine reactions are different, we can refer not only to the evolutionary psychology, as we have already illustrated with the studies of Buss, but also to those which have been carried out in some animal species, especially in the anthropomorphic monkeys (mainly chimpanzees, but also in macaques, baboons and other species of monkeys). There are basically two reasons for this. The first is that these animals are those closest to us and therefore with psychological, physiological and homeostatic characteristics similar to human ones. In monkeys, males exhibit behaviours that are important for the control of the sexual activities of females, which tend instead to be autonomous and free. The purpose of control is to maintain the relationship. Sometimes, however, it manifests itself with violence, coercion, and oppressive vigilance, as happens in humans, but never with the suppression of the unfaithful partner. The monkeys, almost all of them, are structured as harems and therefore with the control of the sexual activities by an adult male and dominant on his group of females, even if it is true that it does not always succeed well.

We should not be surprised by this because, if we want to, there are similar situations in men too; in many Middle Eastern countries a man can have multiple wives, in the West, it can be overcome only with divorce, which is equal, this is true, but which basically reveals a strong tendency of man to have sexual relations possibly with more women and at the same time (polygyny), exceptionally the opposite happens if not in fraternal polyandria (polyandry) accepted only in some archaic societies and limited to a few areas of the world. In short, jealousy has a fundamental biological function regulating the maintenance of a sexual and sentimental relationship between partners, important is not to overdo it, as animals teach us.

Recommended readings
Aaron, B. 1990. Envy and jealousy. Canadian Journal of Philosophy, 20(4): 487-516.
Buss, D.M. 2000. The dangerous passion: Why jealousy is as necessary as love and sex. Free Press, New York.
Ekman, P. 1971. Universal and cultural differences in facial expressions of Emotion. In: J. Cole (Ed.), Nebraska Symposium on Motivation, 19: 207-282. University of Nebraska Press, Lincoln.