As you saw in Section 5-5, most early behaviorists assumed that inherited biological differences are not important for the development of behavior. Instead, they assumed that the development of virtually all animal and human behavior is due to learning. Generalizing from this assumption, early behaviorists asserted that behavioral differences among species are the result of environmental differences, not inherited biological differences.

In addition, early behaviorists assumed that associative learning generally works in the same way regardless of the species. That is, if the behaviors of various species differ mostly because of environmental differences that lead to differences in what is learned, then it really doesn't matter which species researchers use to study learning. This assumption allowed early behaviorists to study any animal species of their choosing, most often rats (see Beach, 1950), and then claim to have discovered general principles of learning — principles true for all species.

Beginning around 1960, these assumptions began to be seriously questioned primarily by psychologists studying learning in species other than rats. It became apparent to these psychologists that species differed in what and how they learned (see, for example, Breland & Breland, 1961). It should be obvious to those of you who own dogs and cats that these two species learn different things and learn them in different ways. Dogs, for instance, can learn to do some things (depending on the breed) simply when rewarded with praise ("that's a good girl!"), whereas cats don’t seem to respond to praise at all. Martin Seligman (1970, 1971) argued that each species learns some associations more easily than others and proposed a theory to explain this (see below). He called this idea biological preparedness, which may be defined as an innate (inborn) tendency to learn certain kinds of associations relatively easily. For example, rats easily learn mazes, whereas humans generally are not good maze learners; and tend to easily get lost in mazes that rats probably would find easy to learn.

The notion of biological preparedness leads to an obvious question: what causes a species to be biologically prepared to learn some associations more easily than others? It seems plausible that the members of each species have innate tendencies to learn associations that were important for their evolutionary ancestors to learn in order to survive longer and, hence, to reproduce more (see the discussion of evolution and evolutionary biology in Section 8). The fact that virtually all rats are good maze learners, for example, may be linked to the fact that they evolved from (and are) burrowing creatures: it probably is important for burrowing creatures to easily learn to navigate maze-like burrows. Most humans are not good maze learners, perhaps because neither we nor our evolutionary ancestors needed to navigate maze-like pathways in order to survive.

A possible example of the evolution of biological preparedness in humans is the development of phobias through learning. We easily learn to fears objects or situations that probably were dangerous for our evolutionary ancestors. For example, young children easily learn animal phobias. In fact, the tendency to do so emerges at an age, about three years, during which children have become highly mobile — a characteristic that often results in their periodically ending up some distance from adults, who, because of the distance, would have a difficult time protecting if a dangerous situation arose, such as the sudden appearance of a carnivorous animal. Our ancient hominid (human-like primate) ancestors often lived in arid environments — environments in which other, perhaps unfriendly, hominids and dangerous animals could easily see them from far away: there were few trees or other tall objects to obstruct vision. This would have proved a dangerous combination for children who had wandered too far away from adult caretakers.

In such environments, these children would have been very vulnerable to attacks. Children who easily learned to fear animals with which they had had a negative experience in the past would have survived longer, on average: they would have been more likely to avoid places in which these animals congregated and also more likely to quickly run towards adults when seeing or hearing these animals. If the ability to easily learn animal phobias was associated with biological heredity, then this ability would tend to get passed on to future generations. Eventually, all other things being equal, the ability to easily learn to fear animals would become virtually universal in hominids, including modern humans. The fact that many animal phobias disappear after about ten years of age also is consistent with this theory: by this age, humans are much better at knowing where danger may lurk as well as at defending themselves from attacks.

The Classical Conditioning of Taste Aversion

Another example of biological preparedness is taste aversion, which is a type of classical conditioning in which an individual learns to avoid the taste of something when it has been paired with sensations of nausea. Kendra Van Wagner (undated) provided an excellent example:

I once had an acquaintance who told a very vivid story about eating a chicken enchilada while on vacation. Hours after eating the enchilada, she became violently ill. For years after that, she was unable to bring herself to eat a chicken enchilada and even felt queasy when she smelled foods that reminded her of that particular dish. This was despite the fact that she knew that her illness was not connected to eating that particular item. In reality, she had picked up a nasty stomach virus from one of her traveling companions who had been ill just days before the trip.

What's interesting about this example is that the person knew that the enchilada did not make her sick, yet her body reacted as if it had. This shows that classical conditioning can have strong involuntary (automatic) effects on behavior.

In order to better see what's going on with taste aversion, let's look at a fictional example. Let's say that you ate some tainted sausages and, several hours later, developed food poisoning. It is likely that you will avoid eating sausage in the future, perhaps for years, as in the enchilada example. Figure 1 outlines the classical conditioning of taste aversion using this example.

Figure 1. The classical conditioning of taste aversion

John Garcia and his colleagues studied taste aversion in rats for several decades (Garcia, Ervin, and Koelling, 1966; Garcia, Kimeldorf, and Koelling, 1955). During the early 1950s, they studied the effects of radiation on rats: the recent development and proliferation of nuclear weapons made this an important research topic for many scientists. In their research, Garcia and his colleagues used a strong dose of X-rays to irradiate the rats — a procedure that induced “radiation sickness,” which leads to vomiting and nausea (along with other symptoms) after several hours. They always irradiated the rats in a cage containing a plastic water bottle, whereas the cage in which the rats lived contained a glass water bottle. They noticed that, after the rats had been irradiated, most of them would never again drink from the plastic water bottle even though they had drunk from it before. Furthermore, although the rats seemed to avoid the water in the plastic water bottle, they continued to drink from the glass water bottle in their “home” cages.

What do you think caused this change in behavior? The rats were drinking from a water bottle that gave a “plastic taste” to the water. While in the cage with the plastic water bottle, they were subjected to large doses of X-rays. Several hours later, they became “sick to their stomachs” and began to vomit. When placed in this cage in the future, the rats refused to drink from the plastic water bottle. One could infer that the rats no longer liked the taste of the water and that, perhaps, they even felt something like disgust when they tasted the water. Such an emotional response could lead to a refusal to drink from the plastic water bottle. Thus, the easiest way to make sense of this change in behavior is to suppose that the rats had been classically conditioned to experience a negative emotional response (something like our emotion of disgust, perhaps) when tasting the water in the plastic water bottle (see Figure 2).

Figure 2. An example of Garcia's studies of taste aversion

In taste-aversion conditioning, the animal learns to avoid a particular taste because it is paired with sensations of nausea. According to Garcia, humans and other mammals have evolved the ability to learn associations between tastes and sensations of nausea because this ability is biologically adaptive: it leads to increased survival and reproduction. If this learning ability is linked to heredity, then the ability will get passed down to future generations until it becomes virtually universal in the species.

Study Questions for Section 5-12

1. What assumptions of early behaviorists led them to believe that they could discover general principles of learning — principles true for most or all species — by studying rats?
2. How would you define "biological preparedness" in your own words?
3. How is biological preparedness thought to be related to evolution?
4. What are some reasons in support of the idea that humans may be biologically prepared to develop certain types of phobias through classical conditioning?
5. How would you define "taste aversion" in your own words?
6. What is an example of the learning of a taste aversion in your own life?
7. In the development of taste aversion, an individual is learning an association between which two events?
8. How did John Garcia and his colleagues first discover taste aversion in rats?
9. In what way is the learning of taste aversions adaptive for animals (that is, how might it increase survival and reproduction)?

Go to Quiz 5-12 questions

Go to Readings Section 5-13

NOTE: IN FUTURE, INCLUDE DISCUSSION OF ARTICLE BY DAVEY, 1995, AND OTHER CRITIQUES OF BIOLOGICAL PREPAREDNESS