"Complex as it is, much of the vast network of cellular functions has been successfully dissected, on a microscopic scale, by the use of mutants in which one element is altered at a time. A similar approach may be fruitful in tackling the complex structures and events underlying behavior, using behavioral mutations to indicate modifications of the nervous system. Drosophila offers the same advantages to such a study as it did to classical genetics, namely, large numbers and short generation time, to which now may be added an enormous store of accumulated knowledge concerning the organism. Containing about 105 neurons, the fly's nervous system is roughly halfway, on a logarithmic scale, between a single neuron and the human brain, and the fly is possessed of a rich repertoire of behavior."