> the natural environment will select for

What do you mean by this?

Natural selection AKA "survival of the fittest" only works over the course of thousands or millions of years. Otherwise, Mars would be pretty much stuck with whatever people it (hypothetically) had. Especially if you're talking about a colony that decides to make itself independent of Earth.

On Earth, we can be selective of who we would (hypothetically) send to Mars. But wouldn't we select loyalists to ourselves? Unless... we make Mars a penal colony. ;-)

Also, "community spirit" can mean obedience to the strict existing hierarchy, for the preservation of the community.