Muscle alone is not enough.

Irritability, the property of response to the forces in the environment , is present in even the more primitive living cells. If a weak electric shock or touch is applied to an amoeba, it will immediately respond with a movement exemplified by a flow of its protoplasm. It will also respond to temperature, oxygen, pH, and various other environmental stimuli. Yet this primitive single-cell organism has no observable specialized "sensory" system. It is "all sensor". This state of affairs has become incredibly refined as we move up in the evolutionary scale. Nevertheless a fundamental principle has remained the same : there is an enormous ratio of sensory input capability relative to motor output capability. For humans, it probably is not feasible to estimate with any precision, but it is compellingly evident that the sensory side is many-fold greater than the motor side, perhaps even in ratios of billions or trillions to one. The philosophical question is : what is the function that nature has achieved by providing such a rich sensory capability, and what is its role in relation to patterns of behavior? I would like to speculate a bit on this matter, particularly on how sensory feedback relates to re-habilitative engineering. Experimentally, it has been demonstrated many times that various sensory responses are coordinated into a whole that provides a multi-dimensional "solid" image of the environment. This image permits all the processes of survival to take place by focusing needs and coordinating them with environmental resources, the global expectation being optimal fulfillment for the living system. Loss of one sense, or even of more than one sense, in higher living forms does not necessarily destroy this environmental imacre_ thnnoh