2023 Volume 37 Issue 2 Pages 235-247
Textbooks on behavior analysis and the psychology of learning conventionally refer to experiments on vertebrate animals such as humans, monkeys, dogs, cats, rats, and pigeons when explaining the basics of respondent and operant conditioning. However, conditioning occurs not only in vertebrates but also in invertebrates. In arthropods, annelids, mollusks, and flatworms, conditioning is easily confirmed. Even in echinoderms, conditioning seems to be possible, at least in starfish. No reports of unicellular organisms, sponges, or cnidarians reliably demonstrate conditioning. There is a theory that the ability to learn through conditioning arose during the Cambrian Period, the beginning of the Paleozoic Era, and that this was one of the triggers of the Cambrian Explosion. But, animals that inhabited the Precambrian Ediacaran period may also have been capable of learning through conditioning. The conditioning ability found in various animal species may have been acquired independently during the evolutionary process, but I suggest that it was inherited from a common ancestor species until today. In this case, the conditioning ability has been inherited for about 600 million years (555 million years to be exact).
