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H. De Cruz (2006) Why are some numerical concepts more successful than others? An evolutionary perspective on the history of number concepts. Evolution and Human Behavior 27:306–23.
M. H. Fischer (2003) Cognitive representation of negative numbers. Psychological Science 14:278–82.
J. S. Lipton & E. S. Spelke (2006) Preschool children master the logic of number word meanings. Cognition 98:B57–B66.
S. Nichols (2002) On the genealogy of norms: a case for the role of emotion in cultural evolution. Philosophy of Science 69:234–55.
J. Vlassis (2004) Making sense of the minus sign or becoming flexible in “negativity”. Learning and Instruction 14:469–84.