The Evolution Of Behavior

JOURNAL OF THE EXPERIMENTAL ANALYSIS OF BEHAVIOR

1984, 41, 217-221

NUMBER

2 (MARCH)

THE EVOLUTION OF BEHAVIOR B. F. SKINNER
HARVARD UNIVERSITY

Evolutionary theorists not only point to the I suggested that well established geological survival value of the present structure and changes could have supplied some of the necesfunction of an organism, they try to recon- sary sequences ofcontingencies. It would not struct earlier stages which should also have be hard to teach a fish to jump from a lower had survival value. An example of current level to a higher one. One could reinforce interest is the flight of birds. Feathers may have swimming across an underwater barrier, slowly evolved first as thermal insulation, but what raise the barrier until it reached the surface, aboutwings? Were they adaptations of fore- and then raise it so that it became the wall of limbs which first helped animals run faster or a second tank. As the levels of water slowly septhat helped tree animals leap from branch to arated, the fish would jump with greater and branch or from branch to ground? (Even when greater force. Something of the same sort, over a feature first evolved because ofconsequences a very different time span, may have happened quite different from those which explain its if the shallow, graveled bottom of a river in current survival value, a plausible early his- which salmon breed moved upstream as the tory is still needed.) Among the features to be river changed and as rapids and falls interexplained in this way is behavior. The current vened between thegraveled bottom and the survival value of reflexes and the released ocean. A different geological change has been sugpatterns of behavior studied by ethologists may be clear, but can we construct plausible gested (Carr, 1967) to explain the behavior of sequences through which they could have the turtles that feed along the coast of Brazil but swim more than a thousand miles to evolved, with survivalvalue at every stage? The first behavior was presumably simple Ascension Island where they breed. Apparently movement-like that of the amoeba reaching they once swam to nearer islands which have out into new territory and hence increasing its disappeared. As a third example, I cited the chances of finding materials necessary for its behavior of the Atlantic eel, which travels survival. A plausiblesecond step was sensing, from either American or European rivers to as the result of which movement could take the a breeding ground near the Sargasso Sea. These organism away from harmful stimuli and long journeys are taken only once, and it is closer to useful materials. The assignment of quite unlikely that they could have occurred different organs to sensing and moving should first in theirpresent form as variations. Before have led to the evolution of connecting struc- North America and Europe separated, howtures, and eventually to tropisms and reflexes. ever, the distances must have been very short. The released behavior patterns studied by The present behavior could have evolved as ethologists also presumably evolved through each generation went at most a few centimeters increasinglycomplex stages. It is unlikely that farther than the preceding. Like most evolutionary theories, these are many current instances occurred first in their present state as variations which were then speculations, but they appeal to known geoselected by survival. In my paper "The Shap- logical changes that could have provided the ing of Phylogenic Behavior" (Skinner, 1975), conditions under whichcomplex innate behavior was shaped. So far as I know, ethologists This paper was read at the First European Meeting have not given much attention to plausible on the Experimental Analysis of Behavior, Liege, Bel- histories of this sort. Some, indeed, have quesgium, August 1983. Reprints may be obtained from tioned whether reproduction with variation B. F. Skinner, Department of Psychology and...