Forget about Hallmark cards and chocolate. Just in time for Valentine’s Day, scientists are announcing the results of an astonishing two-decade-long study that explored the connection between insecure infants and relationship problems in young adults. Turns out the kind of baby you were at 12 months can say a lot about the kind of lover you will be at 21.

“If you are more insecure when you are 1, you are more likely to experience more negative emotions in your relationship with your current partner when you are 21,” psychologist Jeffry Simpson at the University of Minnesota said.

People from Sigmund Freud on down have made arguments about the role of early relationships in later life. But Mr. Simpson and his colleagues have shown for the first time, in a paper in the current issue of the Journal of Personality and Social Psychology, an empirical connection between early behavioral patterns and romantic relationships years down the road.

The study closely tracked 78 people over a quarter-century, starting when they were babies. Mothers and infants were brought into a laboratory, and the mothers were asked to leave briefly. The infants became upset, of course, but the psychologists were interested in what happened when the mothers returned. Some infants clung tightly to their mothers and sought comfort. In a little while, they calmed down. But others refused to calm down even after lengthy soothing. And some babies refused to turn to their mothers for comfort at all.

Mr. Simpson said research has shown that secure infants turn to their parents when they are upset: “The kid learns, ‘I can count on my parents to calm me down.’ They learn to turn to others. Whereas insecure kids learn that my parent is either rejecting, or they learn my parent is neglectful. Or ‘I have to protest to get attention.'”

The researchers checked in with the children again when they were in first through third grade. They asked teachers how each child compared in social skills with other children in the class — especially when the child was upset. Did she act out her anger or reach out to others to solve the problem?

The next check came at another developmental milestone, when the kids were teenagers. The psychologists studied how the adolescents reached out to their best friends for support: “Do you rely on your best same-sex friend at 16 to calm you down, or do you distract yourself?” Mr. Simpson asked.

Finally, the researchers studied the people when they were between ages 21 and 23. They asked the volunteers how often they felt happy or sad in their romantic relationships. The volunteers’ romantic partners were asked to describe the relationship as well. Finally, the couples were presented with a conflict and given 30 minutes to try to resolve it. Researchers videotaped the couples as they dealt with the problem and the emotions it produced.

“We find if you are insecure at age 1, that predicts being rated as being less socially competent than your peers during grades one-two-three, which predicts less reliance on your best same-sex friend when you are upset at 16, which then predicts more negative emotion in a romantic relationship at age 21 to 23,” Mr. Simpson said.

Does this mean all insecure infants are doomed to a lifetime of unhappiness? Mr. Simpson argued otherwise. Human destiny is not so circumscribed, he said. What the study showed is how each developmental step influences the next, positively or negatively. While it is certainly best to be started in the right direction, people can always learn the skills needed for successful relationships.

At its core, said Brooke Feeney, a social psychologist at Carnegie Mellon University who published another study in the same journal, research into the factors that predict happiness in our personal lives shows a paradox about relationships — and a timely lesson for Valentine’s Day.

Contrary to the popular American myth that people left to fend for themselves become strong and independent, the psychological research seems to show exactly the opposite is true: It is the people who are confident enough to reach out to others for help — and to whom help is given — who become truly capable of independence.

Like those crying infants in Mr. Simpson’s study who turned to their mothers for support and, once comforted, resumed their explorations of the world, Ms. Feeney found that romantic partners similarly become more independent once their emotional needs are met.

“It is a lot easier for people to take risks and accept challenges when they know someone is available to help them and comfort them if something goes wrong,” Ms. Feeney said. “The most secure individuals are able to turn to other people for support.”