Table 2. Evidence for heterogeneity in the behavior of the population.

type of player	experiment 1	control	experiment 2
pure cooperators	1	1	6
mostly cooperators	2	2	3
conditional cooperators	125	92	91
mostly defectors	26	36	36
pure defectors	15	38	33

Frequency of the different types of players in the three parts of the experiment. Mostly defectors are people who defected more than 2/3 of the times in any context, mostly cooperators are those who cooperated more than 2/3 of the times in any context, and conditional cooperators follow the strategy described in the main text.