It’s about using chemical bribery to make sure we stick around, cooperate and invest in each other, and particularly in the survival-critical relationships we have with our lovers, children and close friends. This is an evolutionary control of which we are hardly aware, and it brings many positive benefits.

The addictive nature of these chemicals, and our visceral need for them, means that love also has a dark side. It can be used as a tool of exploitation, manipulation and abuse. Indeed, in part what may separate human love from the love experienced by other animals is that we can use love to manipulate and control others. Arguably our greatest and most intense life experience can be used against us, sometimes leading us to continue relationships with negative consequences in direct opposition to our survival.

Anna Machin, evolutionary anthropologist, and author of Why We Love: The New Science Behind our Closest Relationships asks her subjects to consider whether love can ever be negative. The vast majority say no for, if love has a darker side, it is not love, and this is an interesting point to contemplate.

But if they do acknowledge the possibility of love having a less sunny side, their go-to example is jealousy.

Jealousy is an emotion and, as with all emotions, it evolved to protect us, to alert us to a potential benefit or threat. It works its magic at three levels: the emotional, the cognitive and the behavioural. Physiology also throws its hat into the ring making you feel nauseous, faint or flushed.

When we feel jealousy, it is generally urging us to do one of three things: to cut off the rival, to prevent our partner’s defection by redoubling our efforts, or to cut our losses and leave the relationship. All have evolved to make sure we balance the costs and benefits of the relationship. Investing time, energy and reproductive effort in the wrong partner is seriously damaging to your reproductive legacy and chances of survival.

The answer very much depends on our gender.

Men and women experience jealousy with the same intensity. However, there is a stark difference when it comes to what causes each to be jealous. One of the pioneers of human mating research is the American evolutionary psychologist David Buss and, in his book The Evolution of Desire (1994), he details numerous experiments that have highlighted this gender difference.

In one study, in which subjects were asked to read different scenarios detailing incidences of sexual and emotional infidelity, 83% of women found the emotional scenario the most jealousy-inducing, whereas only 40% of men found this to be of concern. In contrast, 60% of men found sexual infidelity difficult to deal with, compared with a significantly smaller percentage of women: 17%.

The reason for this difference sits with the different resources that men and women bring to the mating game. Broadly, men bring their resources and protection; women bring their womb. If a woman is sexually unfaithful and becomes pregnant with another man’s child, she has withdrawn the opportunity from her partner to father a child with her for at least nine months. Hence, he is the most concerned about sexual infidelity.

In contrast, women are more concerned about emotional infidelity because this suggests that, if their partner does make a rival pregnant and becomes emotionally involved with her, his partner risks having to share his protection and resources with another, meaning that her children receive less of the pie.

Emotional intelligence sits at the core of healthy relationships. To truly deliver the benefits of the relationship to our partner, we must understand and meet their emotional needs as they must understand and meet ours. But, as with love, this skill has a darker side because to understand someone’s emotional needs presents the possibility that you can use that intelligence to control them. While we may all admit to using this skill for the wrong reasons every now and again – perhaps to get that holiday destination we prefer – for some, it is their go-to mechanism in their relationships.

The most adept proponents of this skill are those who possess the Dark Triad of personality traits: Machiavellianism, psychopathy and narcissism. The first relies on using emotional intelligence to manipulate others, the second to toy with other’s feelings, and the third to denigrate others with the aim of glorifying oneself.

For these people, characterised by exploitative, manipulative and callous personalities, emotional intelligence is the route to a set of mate-retention behaviours that certainly meet their goals but are less than beneficial to those whom they profess to love. Indeed, research has shown that a relationship with such a person leaves you open to a significantly greater risk that your love will be returned with abuse.

Research has shown that having a Dark Triad personality, whether you were a man or a woman, significantly increased the likelihood that ‘“cost-inflicting mate-retention behaviours” were your go-to mechanism when trying to retain your partner. These are behaviours that level an emotional, physical, practical and/or psychological cost on the partner such as physical or emotional abuse, coercive control or controlling access to food or money.

Interestingly, however, these individuals did not employ this tactic all the time. There was nuance in their behaviour. Costly behaviours were peppered with rare incidences of gift giving or caretaking, so-called beneficial mate-retention behaviours. Why? Because the unpredictability of their behaviour caused psychological destabilisation in their partner and enabled them to assert further control through a practice we now identify as gaslighting.

It is hard to imagine that, having experienced such a litany of abuse, anyone could believe that love remained within their relationship. But here the power of the lived experience, of allowing everyone to have their ideas about love becomes clearer. Because, while we have many scientific tools to explore love objectively, at the end of the day, there is always an element of our experience of love that is subjective, that another cannot touch. This is no more powerfully evidenced than by the testimony of those who have experienced intimate partner violence.

Love is the focus of so much science, philosophy and literary rumination because we struggle to define it, to predict its next move. Thanks to our biology and the reproductive mandate of evolution, love has long controlled us. But what if we could control love? What if a magic potion existed that could induce us, or another, to fall in love or even wipe away the memories of a failed relationship?

Today we know enough about the chemistry of love for the elixir to be within our grasp. And we don’t have to look very far for our first candidate: synthetic oxytocin, used right now as an induction drug in labour. We know from extensive research in social neuroscience that artificial oxytocin also increases prosociality, trust and cooperation. Oxytocin, as released by the brain when we are attracted to someone, is vital for the first stages of love because it quiets the fear centre of your brain and lowers your inhibitions to forming new relationships.

The other possibility is MDMA or ecstasy, which mimics the neurochemical of long-term love, beta-endorphin. Recreational users of ecstasy report that it makes them feel boundless love for their fellow clubbers and increases their empathy. Researchers in the US have reported encouraging results when MDMA was used in marriage therapy to increase empathy, allowing participants to gain further insight into each other’s needs and find common ground.

Both of these sound like promising candidates but there are still issues to iron out and ethical discussions to have. How effective they are is highly context dependent. Based on their genetics, some people do exactly what is predicted of them. Boundaries are lowered and love sensations abound. But for a significant minority, particularly when it comes to oxytocin, people do exactly the opposite of what we would expect. For some, a dose of oxytocin, while increasing bonds with those they perceive to be in their in-group, increases feelings of ethnocentrism – racism – toward the out-group.

MDMA has other issues. For some people, it simply does not work. But the bigger problem is that the effects endure only while usage continues; anecdotal evidence suggests that, if you stop, the feelings of love and empathy disappear. This raises questions of practicality and ethical issues surrounding power imbalance. If you commenced a relationship while taking MDMA, would you have to continue? What if you were in a relationship with someone who had taken MDMA and you didn’t know? What would happen if they stopped? And could someone be induced to take MDMA against their will?

The ethical conversation around love drugs is complex. On one side are those who argue that taking a love drug is no more controversial than an antidepressant. Both alter your brain chemistry and, given the strong relationship between love and good mental and physical health, surely it is important that we use all the tools at our disposal to help people succeed? But maybe an anecdote from the book Love Is the Drug (2020) by Brian Earp and Julian Savulescu will give you pause. They describe SSRI prescriptions used to suppress the sexual urges of young male yeshiva students, to ensure that they comply with Jewish orthodox religious law – no sex before marriage, and definitely no homosexuality.

Evolution saw fit to give us love to ensure we would continue to form and maintain the cooperative relationships that are our route to personal and, most crucially, genetic survival. It can be the source of euphoric happiness, calm contentment and much-needed security, but this is not its point. Love is merely the sweet treat handed to you by your babysitter to make sure the goal is achieved. Combine the ultimate evolutionary aim of love with our visceral need for it and the quick intelligence of our brains, and you have the recipe for a darker side to emerge. Some of this darker side is adaptive but, for those who experience it, it rarely ends well. At the very least there is pain – physical, psychological, financial – and, at the most, there is death, and the grief of those we leave behind.

Maybe it is time to rewrite the stories we tell ourselves about love because the danger on the horizon is not the dragon that needs to be slain by the knight to save the beautiful princess but the presence of some who mean to use its powers for their gain and our considerable loss. Like all of us, love is a complex beast: only by embracing it in its entirety do we truly understand it, and ourselves. And this means understanding its evolutionary story, the good and the bad.