A Moment of Science

Why Being in Love is Being On Drugs

Papaveraceae

More than 3000 years before our current era, people knew of this plant, the opium poppy or Papaver somniferum. The Sumerians called it "the joy plant" and cultivated it.

Morphine MoleculeIn 1803, the active principle, an alkaloid, was isolated and named morphine. With the invention of the hypodermic needle in the 1850's it became one of the most important drugs then known, most others being useless or worse.

When it was finally realized that the world had not been created specifically for the benefit of humans — an insight that now seems obvious — the question arose: how and why should morphine have such effects on the human nervous system? In 1973, Solomon Snyder and Candace Pert discovered opiate receptors — the molecules that recognize morphine — in brain tissue. A year later, the brain's own morphine, endorphin, was discovered. We now know of at least ten such molecules, all of them short pieces of protein, or peptides.

Because morphine is known for its pain-killing properties, endorphins were first thought of as "the body's natural pain-killers." But they are much more than that, and also play a part in the function of other neurotransmitters such as dopamine.

Genetically Engineered MouseThree years ago, Francesca D'Amato, a researcher in Rome, studied the behavior of mice genetically engineered to be missing one of the key endorphin receptors known as μ.

Unlike normal mouse pups, those lacking μ are not distressed by being deprived of their mother. They get just as upset about being cold or when threatened by adult male mice. Although suspected from studies using anti-opioids in many other mammals including monkeys, this is clear evidence that the endorphins are important in the establishment of social bonding in mice, and, almost certainly, other mammals.

Other neurotransmitter substances are also thought to play a role in social attachment behavior.

Love does come down to molecules. But, then, so does everything else when it comes to living things. At the same time, none of this affects what it feels like to love others, or to desire to be or to feel loved. That it can feel "magical" is a bonus, a part of the human condition. And it ought to make us think that, just as physical characteristics vary a bit from person to person, what it feels like to be a person may also not be quite the same for everyone.