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Abstract

The analysis of biological systems has in many cases revealed almost unbelievable degrees of adaptation, sophistication and efficiency. In the case of sense organs, the ultimate limits to evolution often seem to be imposed by physical constraints rather than by properties of the biological substrate. For example, chemoreceptors respond to individual molecules, mechanoreceptors are sensitive to displacements in the order of 10−8 cm (i.e. the diameter of a hydrogen atom) at the receptive site, and photoreceptors signal the absorption of individual quanta of light. Consequently, when analysing a highly developed sense organ we expect a priori to find a system that is optimized with respect to its structural and functional parameters. However, our knowledge of the mechanisms of Darwinian evolution tells us that in general further improvement could still be possible.