Saturday, April 5, 2008

Black Swans

"Black Swans", as unlikely or unexpected economic events, are currently in the news. This usage was popularized by Nassim Nicholas Taleb. It was based on the old European belief that all swans were white, which was contradicted by the discovery of black swans in Australia. But as I discussed earlier genus and species are human-defined categories. There is no logical contradiction inherent in a black swan, and probabilities related to finding one are really probabilities of finding individuals (animal instances) fitting into ill-defined categories.

Note the first black swan was discovered in 1697, over 150 years before publication of Darwin's On the Origin of Species (1859) and over 250 years before Watson and Crick's A Structure for Deoxyribose Nucleic Acid (DNA) (1953). So seventeenth century notions of species would not include modern concepts of evolutionary descent or DNA similarity. Instead they were based on ideas of fixed categories inherited from Aristotle.

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