A co-worker who has a gracious, giving spirit (and, hence, is unselfish) is infinitely to be preferred to one embodies the opposite traits. That is the person who will be there when times get tough and sacrifice is required. It is the person who will not dart out the door, or dodge responsibility, when something has gone wrong and people have to step up to take responsibility. It is the person who will respect you as a co-worker, who will take a personal interest in knowing that you are well, who will sympathize when you share a problem, who will support you through your trials - I am not talking here about one who is a close friend but rather of the traits exemplified by one who has a loving, kind spirit that is ever alert to show concern for the welfare of others and who is willing to sacrifice for the good of larger aims besides immediate self-interest.
That is what I think of when I think of working with "unselfish colleagues." A genuinely unselfish person is an admirable person by any measure and will usually be humble to boot, not focusing on outward show and phony braggadocio that tends to the sort of self-advancement that is the exact opposite of unselfish.
Such people are known to all of us and are universally admired, or pretty nearly so. And the character traits that underlie the core of such a person cannot be identified or isolated in a superficial study of a few college students playing an artificial game or two.
Common sense will always trump "science" in our understanding of areas such as this and will allow us to sense intuitively what we really don't need people in white lab coats to tell us.