FINANCIAL-MARKETS AS ADAPTIVE SYSTEMS

We show, by studying in detail the market prices of options on liquid markets, that the market has empirically corrected the simple, but ina dequate Black-Scholes formula to account for two important statistical features of asset fluctuations: ''fat tails'' and correlations in the scale of fluctuations. These aspects, although not included in the pr icing models, are very precisely reflected in the price fixed by the m arket as a whole. Financial markets thus behave as rather efficient ad aptive systems.