Noisy Genes

oise is often perceived as being undesirable and unpredictable. The experimental physicist spends a lot of time trying to lower the noise floor of the experimental setup to a level that enables the detection of tiny signals. Although noise is therefore often a source of frustration, noise can be controlled and damped by using, for example, clever electronics, mechanical dampers, or shielded rooms. In biology, however, noise is intrinsic to living systems and cannot be controlled by the experimen-talist. Living systems are inherentlynoisy, and are optimized to function in the presence of fluctuations. In this context, evolution plays the role of the experimentalist in trying to control the noise. During evolution biological cells have been fine tuned and optimized to function in noisy environments, but it's not clear what the biological function of noise is. Does noise increase or decrease the fitness of a cell? Some organisms can exploit fluctuations to introduce diversity into a population, as occurs with certain viruses. In contrast, stability against fluctuations is essential for controlling cell differentiation , as in a developing embryo.