Working with colleagues in The Netherlands, the scholars found about 50 percent of identical twins and 25 percent of fraternal twins shared similar characteristics of loneliness. Research on twins is a powerful method to study the impact of heredity because twins raised together share many of the same environmental influences as well as similar genes, thus making it easier to determine the role of genetics in development.
"An interesting implication of this research is that feelings of loneliness may reflect an innate emotional response to stimulus conditions over which an individual may have little or no control," the research team writes in the article, "Genetic and Environmental Contributors to Loneliness in Adults: The Netherlands Twin Register Study" published in the current issue of the journal Behavior Genetics. Psychologists had previously thought loneliness was primarily caused by shyness, poor social skills, or inability to form strong attachments with other people.
Scholars are becoming increasingly interested in the role loneliness plays in health. Other work by John Cacioppo, the Tiffany & Margaret Blake Distinguished Service Professor in Psychology at the University of Chicago and a member of the research team, shows that loneliness is a risk factor for heart disease. Loneliness is also at the base of a number of emotional conditions, such as self-esteem, mood, anxiety, anger and sociability.
A caring environment can help lonely people overcome their feelings, but the research also shows that in some cases, the impact of heredity is stronger, said Cacioppo, who was joined in the study by Louise Hawkley, a Senior Research Scientist in Psychology at the University.
The lead author of the article was Dorret Boomsma, a Professor of Biolgoical Psychology at the Free University in Amsterdam. Boomsma is one of the world's most prominent researchers on twins and heredity. Other researchers with the project are Gonneke Willemsen of the Free University and Conor Dolan of the University of Amsterdam.
The study was based on data from 8,387 twins in The Netherlands, who have been surveyed regularly since 1991. Smaller, earlier studies done with children suggested that the tendency toward loneliness could be inherited. The Dutch-U.S. study is the first to be done on adults and shows that heredity persists in playing a role in loneliness as people age.
As part of the study, the twins were asked to rate to what extent certain descriptions applied to them, such as "Others don't like me," "I lose friends very quickly," "I feel lonely," and "Nobody loves me."
People noted a wide variety of responses to the descriptions, with 35 percent of the men and 50 percent of the women reporting moderate to extreme feelings of loneliness.
The researchers write that loneliness may have developed early in human evolution as a response by hunter-gathers facing conditions of undernourishment who may have decided not to share their food with their families. By surviving a famine, those early ancestors would be able to propagate during periods of plenty, the researchers theorized. In developing loneliness as an adaptation to survival, these early humans also developed dispositions toward anxiety, hostility, negativity and social avoidance, they said.
The research was funded by the Netherlands Organization for Scientific Research and the U.S. National Institute of Aging.
"The genetics of social behavior is an intriguing and expanding area of research," says Jeffrey W. Elias, cognitive aging specialist at the National Institute on Aging (NIA). "This study suggests there may be a genetic component to loneliness, such that people with a predisposition to loneliness may process social interaction and information differently. This is important to know as we investigate the effects of behavior and emotion on health and longevity."