[thras]

Well, a gene can spread in a small group through drift (even if detrimental). If it allows that group to out-compete the next tribe over, it will spread farther.

Of course, no one has ever seen this in action, so it's pretty unlikely that group selection is very important in evolutionary history.

[grandalf]

Not true. A group does not "out compete" another group. Individuals only survive and reproduce or don't survive or don't reproduce.