1. Ackley, D., Littman, M.: Interactions between learning and evolution. In: Langton, C., Taylor, C., Farmer, D., Rasmussen, S. (eds.) Proceedings of the Second Conference on Artificial Life. Addison-Wesley, California (1991)
2. Ashby, W.R.: Design for a Brain: The Origin of Adaptive Behaviour. Chapman & Hall, London (1965)
3. Baldwin, J.M.: A new factor in evolution. The American Naturalist 30, 441–451, 536–553 (1896)
4. Batali, J., Grundy, W.N.: Modelling the evolution of motivation. Evolutionary Computation 4(3), 235–270 (1996)
5. Cañamero, D.: A hormonal model of emotions for behavior control. In: VUB AIMemo 97U06, Free University of Brussels, Belgium. Presented as poster at the Fourth European Conference on Artificial Life. ECAL 1997, Brighton, UK, July 28-3 (1997)