they got data by inducing monkey fights.

""" We were interested in whether we could induce the monkey society we were studying to change from its status quo of many small fights and a few large ones to having many large fights. We observed that fights in this monkey group range in size from two to 30 or so individuals, with small fights common and large fights very rare. By simulating the society using data we had collected on fight-joining decisions, we found that we could measure the number of monkeys whose propensity to join fights would have to increase to move the system closer to the critical point.