1. Punishment allows the evolution of cooperation (or anything else) in sizable groups;Boyd;Ethology and Sociobiology,1992
2. Darwin, C., 1839. Journal of Researches into the Geology and Natural History of the Various Countries Visited by H.M.S. Beagle, under the Command of Captain FitzRoy, R.N. from 1832 to 1836. Henry Colburn, London.
3. Journal of Researches into the Natural History and Geology of the Countries Visited During the Voyage of H.M.S. Beagle round the World;Darwin,1845
4. The Expression of the Emotions in Man and Animals;Darwin,1872