Cut to the chase: Can sex help start a relationship?

A budding relationship or just a one-night stand? The difference may not be immediately obvious, least of all to those directly involved.

But can sexual desire actually help turn a new acquaintance into a romantic partner?

Research by psychologists at the University of Rochester and Israel’s Interdisciplinary Center Herzliya suggests that sexual desire does more than attract potential partners to each other. It can also encourage nonsexual behaviors—such as showing interest, offering help, and responding with care—that lay the groundwork for emotional connection.

In four studies, researchers examined how sexual desire relates to behaviors that foster romantic connection—and whether activating sexual desire can encourage those behaviors. Their findings, published in the Journal of Social and Personal Relationships, suggest that desire may help initiate the behaviors that support romantic attachment.

“Sex may set the stage for deepening the emotional connection between strangers,” says the study’s lead author Gurit Birnbaum, a social psychologist and associate professor of psychology at IDC Herzliya. “This holds true for both men and women. Sex motivates human beings to connect, regardless of gender.”

The study was limited to heterosexual participants. According to Birnbaum, some believe that men are more likely than women to initiate relationships when sexually aroused. But when researchers focus on subtler relationship-initiating behaviors, such as providing help, that difference disappears: Both men and women try to connect with potential partners when sexually aroused.

“Although sexual urges and emotional attachments are distinct feelings, evolutionary and social processes likely have rendered humans particularly prone to becoming romantically attached to partners to whom they are sexually attracted,” says coauthor Harry Reis, a professor of psychology and Dean’s Professor in Arts, Sciences & Engineering at the University of Rochester.

How attraction shapes behavior

In the first two studies, researchers examined whether sexual desire for a new acquaintance was associated with nonverbal behaviors that signal romantic interest. These included synchronized movements, physical proximity, and other signs of engagement.

Participants, all single and heterosexual, were recruited at a university in central Israel.

• Study 1: Moving in sync. Thirty-six women and 22 men lip-synched to prerecorded music alongside an attractive stranger who was working with the researchers. Participants who reported greater sexual desire also displayed more behaviors associated with romantic interest, including synchronized movements and physical closeness.
• Study 2: Dancing together. Thirty-eight women and 42 men slow-danced with an attractive stranger. Participants who perceived their dance partners as more desirable showed greater synchronization, which was associated with more interest in future interactions.

The next two studies went a step further, testing whether activating sexual desire could actually encourage behaviors that help initiate relationships.

• Study 3: Showing care. Eighty-four participants were briefly exposed to either an erotic image or a neutral image before discussing personal dilemmas with another participant. Those exposed to the erotic image displayed greater responsiveness and caring toward their potential partner.
• Study 4: Offering help. One hundred participants watched either an erotic movie scene or neutral rainforest footage before completing a verbal reasoning task with an attractive stranger. Those who watched the erotic scene were quicker to offer help, spent more time helping, and were perceived as more helpful.

Together, the findings suggest that sexual desire is associated with behaviors that bring potential partners closer—and that sexual activation can directly encourage some of those behaviors.

Why desire fosters connection

What explains the connection between sexual desire and behaviors that promote emotional bonding?

Human sexual behavior evolved to ensure reproduction. But reproduction itself does not require an enduring attachment between partners.

The prolonged dependence of human children, however, may have encouraged the evolution of mechanisms that help sexual partners form lasting bonds and jointly care for their offspring, says Birnbaum, whose collaboration with Reis spans 20 years, dating back to her postdoctoral days at the University of Rochester.

“Throughout human history, parents’ bonding greatly increased the children’s survival chances,” she says.

Previous neuroimaging research has also found that some of the same brain regions—including the caudate, insula, and putamen—are activated during experiences of sexual desire and romantic love. The researchers suggest that this overlap may help explain how sexual activation can influence behaviors that promote emotional connection.

The findings do not establish that sexual desire necessarily leads to a lasting romantic relationship. Instead, they suggest that desire can encourage the warmth, responsiveness, and willingness to help that may allow an attachment bond to develop.

“Sexual desire may play a causally important role in the development of relationships,” says Birnbaum. “It’s the magnetism that holds partners together long enough for an attachment bond to form.”

The research was supported by the Binational Science Foundation.