Student or Learner
Doesn't it have to be only "must have selected" without "for"? I don't know what "select for" means.
43)Animals that develop a competitive advantage against other species through cooperation survive much better if they are constantly ①within sight of one another. Baboons, for instance, who need help from peers to protect themselves against the leopards and hyenas, have a ②decent chance of reaching maturity if they leave their troop. The same conditions must have selected for sticking together as a ③positive survival trait among our ancestors. Of course, as human adaptation began to rely increasingly on culture, additional reasons for togetherness became important. For instance, the more people grew to depend for survival on knowledge instead of instinct, the more they ④benefited from sharing their learning mutually. A ⑤solitary individual under such conditions became an idiot, which in Greek originally meant a “private person” ─ someone who is unable to learn from others.
It's part of the language of evolutionary biology. Natural selection "selects for" some traits but not others. Some traits are selected for.