Re: Allan Isaac's suggestion about choice behavior being shared with animals. This discussion takes us back to Adam Smith, and his question about whether dogs trade. For Malthus, the key issue was that humans have foresight, and can therefore anticipate the consequences of actions which have not yet happened in such a way as to make plans that avoid negative consequences (like too many children). Malthus also indicated that human foresight led to the voluntary organization of institutions like private property, marriage, and markets. Darwin's natural selection mechanism for evolutionary adaptation among animals is Malthus' economic agents without foresight. See Sandra Peart and David Levy's recent essay on "Happiness, Progress and the 'Vanity of the Philosopher'" at http://www.econlib.org/library/Columns/y2005/PeartLevymalthus.html. I also have a piece now written on Malthus, which will be available in the next couple weeks. Ross Emmett