Love is difficult to define, yet it is an almost ubiquitous part of the human experience. It is closely intertwined with trust, attachment, and intimacy, and yet is none of these things alone. When we talk about love, we often mean romantic pair bonding, but love also underpins our relationships with close friends and family members.

The evolutionary basis for love is deceptively complex. At first glance, it makes sense for positive feelings to be associated with behaviours that promote the survival and reproduction of a species. Of course, falling in love feels good: for most of evolutionary history, it was a crucial step towards passing on one’s genes to the next generation.

“Of course, falling in love feels good: historically it’s been a crucial step towards passing on one’s genes to the next generation”

But love extends beyond reproduction. It includes long-term attachment and commitment, which are not strictly necessary for producing offspring. Evidence from non-monogamous species shows that individuals can reproduce successfully without forming deep emotional bonds. Instead, romantic, platonic, and familial love appear to serve a more subtle function: building stable connections between individuals for mutual support. These selective social attachments rely on remarkably similar neural and hormonal mechanisms. This may seem surprising given how differently we categorise friends, family, and romantic partners, but it becomes obvious when we consider the shared role these bonds play in social species like humans. In the short term, however, romantic love remains biologically more intense – and socially more charged – than other forms of attachment.

Falling in love starts with stress. Forming any new connection, romantic or otherwise, can involve anxiety and uncertainty, acting as a biological signal that tells us we need support from others. While love tends to reduce anxiety in the long term, the early stages of romance can be stressful in themselves. Cortisol release and activation of the sympathetic nervous system trigger the sweating, racing heart, and nausea that many associate with being around a crush. This heightened state of alertness may help us cope with neophobia – the fear of new things – when navigating unfamiliar situations. In this sense, the positive stress of falling in love pushes us out of our comfort zones, encouraging the formation of new behaviours that may prove beneficial in the long term.

“That goes some way towards explaining why people in love make spectacularly questionable decisions”

Countless metaphors liken love to a drug, and biologically speaking, the comparison is not far off. Love is chemically rewarding: it induces a flood of signalling molecules that tell the brain to keep seeking out a particular person. In the early stages, this process is governed largely by the limbic system. Dopamine activates reward pathways, noradrenaline contributes to the euphoric ‘high’ of infatuation, and reduced activity in the frontal cortex lowers inhibition and critical judgement (which goes some way towards explaining why people in love make spectacularly questionable decisions). These systems also interact with other brain regions; for example, the hippocampus plays a role in memory formation, making us feel positively about familiar people (which may justify why many of us keep making the same mistakes with our exes).

Infatuation, however, is not permanent. Following our initial attraction comes the longer phase of attachment, shaped largely by the hormones oxytocin and vasopressin. Oxytocin dampens sympathetic nervous system activity, reducing cortisol release and calming the racing heart associated with early attraction. It is closely linked to feelings of trust, safety, and emotional security. Vasopressin, meanwhile, is associated with protective behaviours and can contribute to jealousy and territoriality. Together, these hormones help stabilise relationships by reducing anxiety and stress, lowering aggression, and reinforcing social bonds that persist beyond the initial rush of attraction.

Love, therefore, has a complicated relationship with stress. Low levels of acute stress, such as those experienced when forming new connections, can be beneficial, motivating us to seek out and maintain meaningful relationships. Chronic stress, however, tells a very different story. When positive social bonds are absent, prolonged activation of the stress response can become harmful rather than helpful. The answer is not to rush into romantic relationships to avoid loneliness, but to invest in strong networks of friends and family. By cultivating communities that offer stability and support, we can reap the benefits of the safest, most enduring forms of love–and perhaps feel a little less alone along the way.