Unselfish people not liked by fellow group members

When working in small groups, each person plays certain roles. If someone is unselfish, recent research suggests this does not lead to popularity among other group members:

Unselfish workers who are the first to offer to help with projects are among those that co-workers like the least, according to four separate social psychology studies.

In the most recent study, entitled “The Desire to Expel Unselfish Members from the Group,” psychologists found that unselfish colleagues come to be resented because they “raise the bar” for what’s expected of everyone. As a result, workers feel the new standard will make everyone else look bad.

“It doesn’t matter that the overall welfare of the group or the task at hand is better served by someone’s unselfish behavior. What is objectively good, you see as subjectively bad,” said study co-author Craig Parks of Washington State University. The paper was published in the Journal of Personality and Social Psychology.

This is an interesting finding. The article goes on to say that some of the other participants thought the unselfish person had ulterior motives. The unselfishness was unsettling for other participants who sounded like they expected each person to play for themselves rather than think about the greater good.
I wonder if these findings would be any different if the participants were not all undergraduate students. And what would it take for groups to accept the unselfish behavior – repeated offers to help from the unselfish member, time, failure on the part of other members?