Darwin and Animal Behavior

For many thousands of years, at different times and in different parts of the world, humans have studied their fellow creatures in an attempt to obtain a better understanding of their behavior. Toward the end of the eighteenth century, an increasing amount of observational – and occasionally experimental – research on behavior took place in Western Europe. Nonetheless, the foundations of the contemporary science of behavior were mainly provided by the evolutionary theories and the ensuing debates of the nineteenth century. Of these, the key event was, of course, the publication in 1859 of Charles Darwin’s ‘On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life’ (henceforth referred to as ‘The Origin’). From his youth, Darwin continued to maintain a keen interest in behavior. An early hobby was collecting beetles, and it is clear that he was intrigued as much by how they and other insects behaved as by their bodily structures. For decades, he maintained notebooks on behavior, read widely on the subject, and exchanged letters full of questions about the behavior of a wide variety of species, with correspondents throughout the world. Darwin’s concern with behavior becomes evident in ‘The Origin’ when he discusses what he saw as four major difficulties with his theory. The third of these was that of answering the question: ‘‘Can instincts be acquired and modified through natural selection?,’’ and in Chapter 7, he gives his reasons for believing that behavior was as much subject to natural selection as a bodily characteristic. He starts by acknowledging that some forms of instinctive behavior may derive from habits acquired by a previous generation, as Lamarck had argued 50 years earlier. But the core argument of the chapter is that ‘‘it can clearly be shown that the most wonderful instincts with which we are acquainted, namely, those of the hive-bee and of many ants, could not possibly have been thus acquired.’’ Spelt out with many examples, his simple but conclusive point is that in a number of insect species various innate behaviors are displayed only by sterile individuals. This means that ‘‘a working ant . . . could never have transmitted successively acquired modifications of structure or instinct to its progeny.’’ He then proceeds to the ‘‘climax of the difficulty; namely, the fact that the neuters of several ants differ, not only from the fertile females and males, but from each other, sometimes to an almost incredible degree.’’ Citing both his own measurements and data from others showing variation in the size and