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The evolutionary and chemical reasons for intimacy

By skye c. cleary 6-7 minutes

In her new book, Why We Love: The new science behind our closest relationships, the evolutionary anthropologist Anna Machin argues that love is “a highly complex, multifactorial thing”. To make sense of it requires what she calls an “expansionist” approach. To this end snippets from anonymized interviews are placed throughout the book, and each of the ten chapters covers a different reason for love, including “Attachment”, “Motivation” and “Control”. Moreover, Machin borrows “ideas and techniques from other human-focused disciplines” to seek out evidence and answers “at all levels of explanation”. Her goal is “360° understanding”. Naturally, it is not achieved; apart from fleeting reference to theory of mind, for example, a discussion of philosophy is missing. But Why We Love does provide a wide-ranging overview of its subject and succeeds in making heavy science intelligible.

Machin begins with “Survival”. Evolutionary theory proposes that humans are hard-wired to breed and that our value is based on our perceived ability to reproduce successfully: “The human mating game is based upon a competitive market akin to the stock market, but rather than our worth being expressed in pounds, euros or dollars, it is expressed in mate value”. Machin writes that even people who love each other, but don’t want to or can’t have children, are still looking for mates who would make good parents, even if they aren’t cognizant of it.

Another reason we love is because of addiction. Our brain chemistry incentivizes us biologically to be intimate with others. A neurochemical cocktail of oxytocin, dopamine and serotonin in our brains motivates us to approach potential mates and attempt to copulate – or at least co-operate to perpetuate the species. According to Machin, “At its most basic level, love is biological bribery. It is a set of neurochemicals which motivate you to, and reward you for, commencing relationships with those in your life who you need to cooperate with – friends, family, lovers, the wider community – and then work to maintain them”.

There’s nothing new about these evolutionary and biological theories of love, but in discussing them Machin introduces readers to a new player in the context of love: the brain chemical beta-endorphin. Beta-endorphin – one of the main types of human endorphins – seems to dominate in long-term relationships once honeymoon-phase hormones such as oxytocin and dopamine have subsided. While it’s already known that beta-endorphin is a natural pain-killer that gives us a high after intense exercise, Machin suggests that it is also “the glue of long-term human relationships” because it reduces stress while stimulating attachment and empathy, all of which is important for maintaining close relationships over time.

But endorphins also have a dark side: they make us euphoric, and euphoria is addictive. Chanting, singing and dancing also release beta-endorphins, and when we act synchronously in groups, these chemicals skyrocket. Beta-endorphins, the author argues, may explain why congregations and political rallies are so popular. Because endorphins can overrule critical thinking, they may also explain why some people grant blind allegiance to political and religious leaders.

Machin’s definition of love is admirably broad. We learn, for example, how neurochemistry and attachment theory reveal the possibility that dogs and humans share a reciprocal love similar to love between humans. An American study from 2016 of fifteen pet dogs trained to lie still in an fMRI scanner found that three seconds of verbal praise from their guardians activated the dogs’ brains more than their favourite food.

Similarly, Machin acknowledges that we are capable of loving even when not dealing with tangible beings. Another reason we love, she suggests in a chapter called “Sacred”, is metaphysical. When Christian devotees perceive their spiritual relationship to be intimate and interpersonal, she writes, “It would appear that the relationship between Christians and God is an attachment, has the neural hallmarks of love and recruits the same areas of the brain as when we take part in social interaction with our friends, family and lovers”. This is also true when people interact with celebrities over social media. This mechanism might serve an important social purpose, Machin suggests, because “Celebrities can be havens of safety and security and provide support or advice during difficult times, particularly where this might be lacking in the real world”.

The book is not without its contradictions and overgeneralizations. “What is love?” Machin muses in her conclusion, before answering: “Everything”. Elsewhere the reader is informed that “We will never totally know what love is”. Although her main foci are the evolutionary and chemical, broadly unsentimental reasons for love, Anna Machin also proposes that love is immeasurably subjective, and that humans are complex individuals who seem to be able to overrule their instincts. However, exactly which aspects of our being are beholden to our biology and which are ruled by force of will remains unclear. Nevertheless, Why We Love raises lots of questions worth thinking about, especially when it comes to where we might be neglecting love of our friends, our favourite band and our pets.

Skye C. Cleary is the author of How to Be You: Simone de Beauvoir and the art of authentic living, which was published in July, and Existentialism and Romantic Love, 2015, and the co-editor of How to Live a Good Life, 2020

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