The findings are based on data taken from 229 people aged 50 to 68 over 11 years as part of the Chicago Health, Aging and Social Relations.
Early research treated loneliness as a temporary feeling of distress that had no redeeming value or adaptive purpose.
But Dr Stephanie Cacioppo, who also worked on the study, said: "None of that could be further from the truth."
In 2006, the researchers suggested that evolution has shaped the brain to incline humans toward certain emotions, thoughts and behaviour.
And their new findings that loneliness tends to increase self-centeredness fits this evolutionary interpretation.
From an evolutionary-biological viewpoint, people have to be concerned with their own interests, according to the researchers.
But the pressures of modern society are significantly different from those that existed when loneliness evolved in the human species.
Professor Cacioppo said: "Humans evolved to become such a powerful species in large part due to mutual aid and protection and the changes in the brain that proved adaptive in social interactions.
"When we don't have mutual aid and protection, we are more likely to become focused on our own interests and welfare. That is, we become more self-centred."
Loneliness is on the rise
A recent report by Charities Relate and Relationships Scotland surveyed 5,000 people in the UK and found:
• More than one in eight adults, say they do not have a close friend.
• 45 per cent of UK adults felt lonely at least some of the time.
• 18 per cent felt lonely often or all of the time.
• 17 per cent said they either never or rarely felt loved.
• 83 per cent of people in the UK enjoyed good relationships with their friends.
• 18 per cent of people said they had two or three close friends.
In modern society, becoming more self-centred protects lonely people in the short term, but not the long term, because the harmful effects of loneliness build up over time to reduce a person's health and well-being.
Professor Cacioppo said: "This evolutionarily adaptive response may have helped people survive in ancient times, but in contemporary society may well make it harder for people to get out of feelings of loneliness."
Dr Cacioppo added that when humans are at their best, they provide mutual aid and protection.
She said: "It isn't that one individual is sacrificial to the other. It's that together they do more than the sum of the parts.
"Loneliness undercuts that focus and really makes you focus on only your interests at the expense of others."
The researchers hope that their findings could be used to develop better therapies for lonely people, who have been shown to be more susceptible to a variety of physical and mental health problems.
The vicious cycle
Humans evolved as highly social creatures who need groups for survival - as loners would soon die without social support.
So being cut off from others in our ancient past was "not just sad, but dangerous".
As a result, on feeling alone we start to become more focused on ourselves - in an attempt to work out what has gone wrong, researchers said.
But over time this compounds the problem - as being self-centred will trigger loneliness, or make it worse.
