In the 1950s, Harry Harlow conducted some remarkable, if heartbreaking, studies on infant rhesus monkeys at the University of Wisconsin. The neonatal macaques were separated from their mothers shortly after birth and then, in several different experiments, placed in cages with two surrogate “mother-machines” on which they could nurse through a bottle: the first, a structure made of wire-mesh; the second, a doll made of wood, covered with sponge rubber, then “sheathed in tan cotton terry cloth,” and placed in front of a light bulb radiating heat.

The babies, no surprise, spent most of their time clinging to the soft, warm mother. But this was true even when the bottle of milk was offered on the wire doll only: The newborns would drink from the hard structure and then quickly return to their soft mother. When the monkeys were separated into two groups, one with each type of surrogate, the wire-mothered macaques developed skittishly, responding in terror when a new stimulus—a teddy bear drummer—was introduced in the cage. Those “reared” by the cloth mother were nervous at first, but then playfully explored the foreign object. They were even secure and confident enough to challenge the stranger after a while.

“The wire mother,” concluded Harlow, was “biologically adequate but psychologically inept.” One offered at least a facsimile of connection, the other merely nutrition. True sustenance required both.

Explorers across the spectrum of scientific disciplines have probed and poked at every aspect of the mysterious power of connectivity between beings in an effort to understand the link between social bonding and health and well-being.

Researchers have found that frequent hugging from a partner, for instance, lowers blood pressure and heart rate; that physical stroking increases levels of oxytocin, a hormone associated with maternal behavior and one known to even hard-edged scientists as the “cuddle chemical.” Social touch, as a gajillion studies have suggested, is essential for many species in the kingdom of animals—including we awkward, two-legged kind. It’s fundamental to being part of (and protected by) a clan. It’s a sign of kinship, a “stress buffer,” and may reduce pain in cancer patients.

Connection to another being—be it physical, emotional, or merely proximal—is associated with longer survival. Pet owners appear to live longer after being discharged from a cardiac care unit; spouses survive longer after a serious illness when there is a partner caring for them, or waiting for them after a hospitalization.

Touch even has the power to tell both the dying and the living that they are connected, that each remains a part of the human fabric even as the tide of life changes.

I was moved to read this passage from a 2009 JAMA article that described the “self-care” of physicians tending to terminally ill patients.

Said one doctor: “I always try to figure out some way to touch the patient during the visit . . . shake hands, do even a small part of the physical exam. When I check the blood pressure, I hold the patient’s arm in between my side and my arm, which is both an accurate and intimate technique that helps me feel really connected.”

Yes, connection is an essential part of what makes us human beings. It may even be the most essential part.

Happy Valentine’s Day. May you all feel connected today.