Why We Love: The Nature and Chemistry of Romantic Love

The book's starting point is simple and uncomfortable: passion is not just a pretty emotion, it is a basic drive of the body, similar to hunger or thirst. Hunger pushes you to look for food. Thirst pushes you to look for water. Romantic love, according to the research, pushes a person to seek one specific partner, and only that one, with an urgency that doesn't really obey reason.

This explains why you can lose your appetite, your sleep, and your focus at work because of a single person. It's not being dramatic or lacking willpower: it's a motivational system in the brain switched on, competing with every other priority of the day, including the bill that's due tomorrow.

Think of the coworker who trades his lunch break for three laps around the block just to walk past the desk of the person he likes. From the outside it looks like teenage silliness. On the inside, it's the same kind of circuit that makes someone run after a plate of food after a whole day without eating.

The central idea of the book is to divide what we generically call love into three distinct brain systems, which evolved at different times and serve different functions: sex drive, romantic attraction, and long-term attachment. Each has its own chemistry, its own goal, and can, in theory, work alone, without the other two.

Sex drive looks for partners in general, almost without choosing a face. Romantic attraction picks one specific person and makes the brain focus on them as if the rest of the world had moved to the background. Attachment is what holds two people together after the initial phase of enchantment passes, ensuring long-term partnership.

That's why you can feel desire for someone on the bus, be in love with another person, and at the same time keep a strong attachment to the one who already shares a home and the electric bill with you. The three systems don't always line up in the same direction, and that's where a good part of people's emotional confusion lives.

Sex drive is the most basic of the three systems, linked mainly to hormones like testosterone, present in both men and women. Its function, in the book's evolutionary reading, is simple: push a person to look for sexual partners in general, without requiring a bond or exclusivity.

Unlike what the culture sometimes suggests, desire by itself doesn't create attachment or promise fidelity. It can switch on and off quickly, leaving no major emotional trace, which confuses many people who expect that feeling physical attraction already means being in love.

In practice, that's why you can find someone attractive in the bank line in the morning and, by afternoon, not even remember the person's face. Desire works on a different time scale, and the book takes care to separate this quick spark from the more overwhelming experience that comes in the next system.