SUMMARY
In Chapter VII of the Origin of Species, Darwin proposed thatinstincts were behavioraladaptations that had evolved by natural selection andsexual selection. Darwin provided many examples of instinctive behaviors in animals, and suggested how such behaviors could have evolved. In particular, he proposed that animal social behavior was the result of natural selection acting at the level of “families”, rather than individuals.
In his later book, On the Expression of Emotions in Men and Animals, Darwin elaborated on the idea that behaviors are evolutionary adaptations that have evolved by natural and sexual selection. He explained the roles that emotions play in the biology of animals, and extended those explanations to humans. He argued that emotions are essentially biological processes analogous to other physiological adaptations, and that the methods by which they can be studied are similar to those by which any other inherited trait can be scientifically analyzed.
EVOLUTIONARY PSYCHOLOGY 1.1.5
Near the end of the previous chapter, I mentioned that Darwin proposed in the Origin of Species, that “instincts” were behavioral adaptations that had evolved by natural and sexual selection.
In a chapter in the Origin entitled “Instincts,” Darwin explored this idea in the light of his overall theory of evolution by natural selection. In particular, like many of his contemporaries Darwin was fascinated by the behavior of social insects, especially ants and bees. He pointed out that their highly specialized behavior and mode of reproduction posed a serious problem for his theory, a problem that he needed very much to solve.
Darwin on Instincts
In the chapter on instincts, Darwin was very careful to distinguish between the evolution of intelligence and the evolution of instincts. In the Origin, Darwin did not speculate about the evolution of intelligence at all, but rather confined his discussion to the behavior of non-human animals. However, he did make it clear that he believed that there were strong analogies between some of the instinctive behaviors of non-human animals and similar behaviors in humans.
Darwin initially avoided defining “instincts” directly. Instead, he provided multiple examples of the kinds of behaviors he was referring to when he used the term “instinct.” In other words, he used the kind of functional analysis that I described in the previous chapter. We will see this technique being used over and over again, not only in evolutionary biology as a whole, but especially in evolutionary psychology.
The examples of instincts cited by Darwin in the Origin have the following properties:
1. Instincts are not acquired (i.e. learned) via experience.
2. On the contrary, instincts can be performed by individuals who have never learned how to perform them, nor experienced the same set of stimuli before in their lives.
3. In particular, instinctive behaviors can be elicited from animals that have been raised in isolation since birth (or since hatching, as often the animals being tested were birds).
4. Instincts are stereotyped. That is, they are performed in very much the same way every time, both by the same individual at different times and by most of the members of a given species (i.e. they can be referred to as pan-specific behaviors).
5. Furthermore (and in contrast with many human behaviors), instinctive behaviors do not seem to require judgment or reason on the part of the individuals performing them.
6. By implication, this means that instincts are essentially unconscious; that is, they are not the result of conscious deliberation or intentions.
Darwin also took great pains to distinguish between “instincts” and “habits.” He pointed out that habits are stereotyped behaviors that are acquired during an individual’s lifetime, usually by constant repetition. However, Darwin also believed that some habits could be inherited, especially as the result of use and disuse. In that respect, Darwin clearly believed in the possibility that evolution could proceed by the inheritance of acquired characteristics, a theory proposed a half century earlier by the Frenchman, Jean-Baptiste Lamarck. If he were referring to anatomical or physiological characteristics, we would be safe in rejecting Darwin’s assertion that acquired traits such as habits can be inherited. As August Weismann and others showed, acquired anatomical characteristics (such as missing tails in mice, chopped off by the experimenter) cannot be inherited from parents to offspring.
However, some behaviors are learned from other individuals, and not just from parents to offspring. To the extent that a behavior can be learned or modified during an individual’s lifetime that behavior is essentially an acquired trait that can be passed on (i.e. “inherited”). Some behaviors, in other words, follow the rules of Lamarckian evolution. As we will see, there is evidence that we inherit (via Darwinian mechanisms) the tendency to learn certain behaviors (via Lamarckian mechanisms), and that we learn such behaviors surprisingly easily.
