Mechanistic teleology and explanation in neurobiology: understanding the origins of behaviour

Abstract

As every submarine commander knows, the best and almost the only underwater sense organs which are effective at long range utilize the excellent transmission of mechanical waves through water. And yet when the known examples of sense organs which are adapted to the detection of underwater vibrations were recently reviewed by Frings (1964), almost no substantiated examples could be found among marine invertebrates. Even in shallow water, large animals with excellent eyes spend about half of their time in dim moonlight or in the dark, and the range of vision falls off rapidly with depth, so that objects cannot be seen until they are relatively close. However, most invertebrates have eyes which are not well adapted for the detection of the direction and range of a moving prey. On the other hand, vibrations are set up in the water by any animal which propels itself along, as well as by waves at the surface or choppy water at a shore line. Therefore we can expect receptors for vibrations to be distributed ubiquitously through the marine groups, and to be used to detect prey or enemies, or to allow avoidance of environmental sources of vibration. Perhaps one of the reasons why more examples of sense organs of this type are not known is because we ourselves have nothing similar, because the receptors are inconspicuous, and because the responses depending on them are usually not obvious escape reactions. However, in the last two or three years a number of examples have appeared in different phyla so that the general features of invertebrate underwater vibration receptors have now become apparent. Several of these examples have been discovered at St. Andrews.