K-Selection means that the environment is stable and filled to near capacity with a particular species. Sounds ideal and that it might true for all of us.
Suckers always sacrifice themselves for another conspecific.
Suckers do OK with other Suckers, they do badly with Cheaters. These exchanges are not trivial because being nice to someone else always exacts a cost in your own chances to reproduce while increasing their own. Behavior is speculated to have been highly public and subject to immediate, personal consequences. Jewish Law developed in a time when agriculture made population increases possible and for Cheaters to thrive. The 10 Commandments became necessary to reinstate T4T even among relative strangers.