Trust had to evolve into human behavior as part of an opportunity to gain cooperation based rewards and in turn survival and evolutionary fitness. The absence of trust and conceptual thought processes in human evolutionary history was studied by Joan Strassmann and the U.S. National Academy of Sciences in their book, “In the Light of Evolution : Volume V: Cooperation and Conflict.” Strassmann and the U.S. National Academy of Sciences studied primates that are closely related to humans. They acknowledge:
In other primates, altruism [conceptual problem solving strategies] is strongly biased in favor of kin and reciprocating partners, and it is never extended to strangers… Unlike humans, nonhuman primates show no aversion to inequitable distributions