iol 3: e225. 160. Brandt H, H Ohtsuki, Y Iwasa, K Sigmund (2007). A survey of indirect reciprocity. In Mathematics for Ecology and Evolution, eds. Y Takeuchi, Y Iwasa, K Sato. Berlin: Springer, 21-50. 161. Burnham TC (2007). High-testosterone men reject low ultimatum game offers. Proc R Soc B 274: 2327-