Players in repeated prisoner's dilemma games are likely than those in a one-trial game to cooperate because

i believe the answer is:   psychological  experiment

in this experiment, wilhelm wundt became the first person that implement scientific method in analyzing the pyschological phenomenon.

due to this result, wilhelm wundt also able to make psychology to be acknowledged as a separate scientific field from biology.

answer; they both highlight the power of the situation in determining behavior;

answer; a splinter party;