Specialist and Generalist Strategies in Sensory Evolution

Sensors are the conduits through which biological organisms gain information about their surroundings. Organisms use sensory systems to ascertain external conditions, such that appropriate action can be matched to perceived conditions in a manner that enhances prospects for survival and reproduction. In the perception-coordinationaction loops that flow between organism and environment, sensory systems embody the causal linkages that connect states of an organism’s external world with its own internal, informational states. Sensors thus play a crucial role in determining what kinds of information an organism can have regarding its environment. They determine its perceptual categorical primitives. Like all other parts and functionalities of the body, sensory systems evolve. As with other body systems, evolution of structures and functions are guided by external demands posed by the environment. The possibilities that natural selection can favor or reject are in turn limited by structural and developmental constraints. As with the evolution of other systems, selective pressures in sensory evolution can favor the evolution of systems that subserve sensory functions of more general-purpose kinds or more specialized ones. An analogy can be drawn with the evolution of an animal’s gut—whether the gut permits its owner to digest and utilize many highly diverse food sources, or whether it is specialized to process a narrower range of particular food sources in a more efficient manner. In the sensory realm, a sensory system can be narrowly selective for detecting particular stimuli, or it can be capable of detecting and recognizing a wide range of possible forms. Here we take the sensory system to include not only the end-organs of sensation, which transduce physical energy into neural activity patterns, but also the neural codes and computations that subserve neural information processing. Taken together these subserve the functional capabilities of the system: what it can detect, discriminate, and recognize. The themes of generalist vs. specialist adaptive strategies, of course, run through evolutionary theory, but relatively less has been said of how these issues play out in sensory evolution. Their discussion most often appears under the rubrics of the evolution of behavior, ethology, ecological theories of perception, comparative psychology