 Cooperative outcomes can thus be explained without resorting to the concept of social identity. A social identity explanation appears to be more appropriate in the context of a relatively stable environment, where individuals have had time to make emotional investments (or at least can expect repeated future interactions within the same group). In artificial lab settings, where there are no expectations of future interactions, the concept of social identity seems less persuasive as an explanation of the observed rates of cooperation. On the other hand, we note that social identity does appear to play a role in experimental settings in which participants are divided into separate groups. (In that case, it has been shown that participants categorize the situation as “we versus them”, activating in-group loyalty and trust, and an equal degree of mistrust toward the out-group; Kramer &amp; Brewer 1984; Bornstein &amp; Ben-Yossef 1994.)