Using Evolution By Natural Selection as an Integrative Theme in Psychology Courses

Many who teach the introductory course bemoan the enormous breadth and diversity of our field. How, we ask, can we present psychology in an organized fashion, not as just a hodgepodge of facts and theories? One answer: Use evolution by natural selection as an integrative theme. No other concept can tie all of psychology together as meaningfully. Here are some thoughts about how to use the evolutionary theme in an introductory or more advanced psychology course.

Early in the course, explain clearly the concept of evolution by natural selection and its relevance to all of psychology

Many students hold misconceptions about evolution that can interfere with their ability to apply the concept as the course progresses. Some conceive of evolutionary “fitness” in terms that go beyond the survival and reproduction of genes. Some believe that species can be arranged on an evolutionary ladder, that “lower” species are on their way to becoming humans, or that evolution is guided to meet future conditions or higher moral purposes.

One way to help students overcome such misconceptions is to elaborate on examples of evolution that have been observed and documented in our time, such as the evolution of beak thickness in finches on the Galapagos Archipelago, which has been studied for many years by Peter and Rosemary Grant (Grant, 1991). Over prolonged years of draught the finches evolved thicker beaks, which could crack the harder seeds available, and over years of heavy rain & the same species evolved thinner beaks, efficient for eating the softer seeds the rains produced. What was fit in one situation was not fit in the other. In no case did the species anticipate a change in climate by evolving characteristics to meet it in advance, and we know of no mechanism by which that could happen.

Ask “why” questions throughout the course and categorize answers as proximate or ultimate explanations.

The relevance of evolution to all of psychology can be made clear by pointing out that psychology is the study of behavior and that all behavior is produced by biological mechanisms built through natural selection. The mechanisms of sensation, perception, motivation, emotion, learning, memory, reasoning, and language are products of natural selection, as are all of the mechanisms that make us cultural animals, underlie our social behavior, and allow us to develop personalities. This fact allows us to take a functionalist perspective in every realm of psychology. The psychological processes, traits, and tendencies that characterize our species as a whole came about because they promoted the survival and reproduction of our ancestors’ genes.

For every universal human characteristic introduced in a course, we can ask a “why” question. Why does our visual system exaggerate the physical contrasts in patterns of light? Why do people everywhere sleep about 8 hours of every 24, usually at night? Why do children everywhere, when they have a chance, play in certain predictable ways? Why does essentially everyone have the capacity to feel depressed, given certain conditions, or anxious, given others? By asking such questions and discussing students’ tentative answers, we can help students understand the distinction between proximal causation (the immediate inducers of behavior) and ultimate causation (the evolutionary advantage served by the behavior-producing mechanism). Such questions often lead to lively debate in which students conclude that the two kinds of explanations are compatible with one another and serve different purposes.

Use functionalist, evolutionary accounts as frameworks for organizing behavioral facts, and use the facts to test the accounts.

Suppose, in response to the question of why humans sleep about 8 hours per night, your students suggest more than one plausible evolutionary answer. The sleep pattern might have evolved as a mechanism to restore tissues that wear out from the activities of the day (restoration theory); to keep individuals quiet and hidden at night, when they are most vulnerable to predators and other dangers (protection theory); to conserve energy during that part of each 24- hour day when individuals can do little else to promote their survival (energy conservation theory); or for a combination of these.

With functional theories on the blackboard, the facts that you might want to present about sleep assume additional meaning. They are not simply curiosities but are data for testing theories. The fact that some people (with abnormally low sleep drives) sleep much less than 8 hours per night without tissue damage is evidence against the restoration theory. Across species, differences in the amount and timing of sleep correlate with such factors as vulnerability to predation and amount of time that members must spend feeding, supporting the protection and energy conservation theories. Our knowledge of the physiological regulation of sleep-that sleep is controlled by a circadian clock linked to the day-night pattern of light and dark, and not by any known correlate of tissue damage—provides further evidence for the protection and energy conservation theories and against the restoration theory.

When facts are presented to support or refute a theory, students learn more than facts: they learn how psychologists use facts; they  test theories. The lesson is more compelling if students have developed the theories themselves, and in my experience, students become quite ingenious at developing plausible functional theories after a little practice.

Use Evolutionary accounts to help students overcome the pathology bias.

Many students equate psychology with the study of psychopathology, and, in fact, psychology courses do often emphasize pathology at the expense of function. For instance, introductory presentations of social psychology typically focus on the harmful consequences of conformity, obedience, and concern for approval. Similarly, students often learn about the so-called negative emotions (such as anger, jealousy, fear, and shame) primarily as pathologies. But if these are universal human tendencies, they almost certainly served life-promoting functions to our ancestors. To overcome the pathology bias, we and our students can contemplate the potential evolutionary value of such tendencies before attending to the harmful consequences they sometimes have.

As an example, consider young children’s bedtime protest, which in our culture is often discussed in pathological terms as evidence of spoiling. Why do young children resist going to bed? Some student may suggest that the resistance is not so much to going to bed as to going to bed alone in the dark. Children talk about fear of the dark and fear of monsters hiding in the closet. In hunter-gatherer days, being alone in the dark was undoubtedly dangerous to a child (the monsters were real), and ‘children who protested this condition and drew adult attention were more likely to survive. Such an analysis is supported by cross-cultural data. Present-day hunter-gatherers believe that putting a child to bed alone is an act of child abuse, and in cultures where children sleep with a parent or grandparent bedtime protest is absent (Konner, 1982).

Ask students to critique classic psychological theories from an evolutionary perspective.

All of the grand theories in psychology, even those that place greatest weight on the role of environment or culture in shaping behavior, are implicitly theories of human nature. As such, they should be at least compatible with the theory of evolution by natural selection. We can ask students (as a written assignment or in small-group discussion): Are a theory ‘s basic premises compatible with evolution by natural selection? How might each premise be understood as promoting survival and reproduction? How might the theory be modified to make it more compatible with evolutionary theory, yet consistent with the facts used to develop the theory?

At a minimum, such exercises lead students to identify and think about the basic premises of each theory, and at best they lead to reasoned arguments involving evidence and suggestions for further research.

Describe the limitations of evolutionary, functionalist accounts.

The evolutionary perspective, like any other broad perspective in psychology, has limitations. Functional, evolutionary accounts of specific human tendencies are easy to develop as theories but not always easy to test with facts. Some universal human traits may be side effects of our behavioral machinery rather than directly selected adaptations. Depending on conditions, our learning mechanisms can produce behaviors that are irrelevant to or even contrary to survival and reproduction. These and other limitations- all made famous through the writings of Steven Jay Gould–can be hinted at early in the course and then clarified in the exercises and discussions described above, as the course progresses. Evolutionary theory is not a royal road to understanding in psychology, but it is the best general guide we have.

Use the evolutionary perspective to explain the entwinement of nature and nurture.

At one time psychology tended to treat instincts and learned actions as separate behavioral categories, but today- largely due to the influence of the evolutionary perspective- most psychologists realize that learning and instinct are inseparable. Evolution has not endowed us with one or two all-purpose learning mechanisms, nor with many rigid, unmodifiable behavior patterns. Rather, evolution has endowed us with many behavioral biases, or tendencies, each of which may have its own mechanism of modifiability (learning) built into it. The laws by which we learn about food, about the movements of objects in three-dimensional space, about other people’s minds, and about the grammar of our native language are all apparently different from one another. The behaviors and mental activities through which we explore, assess, and thereby learn in each domain of our world are themselves instincts.

From an evolutionary perspective we can ask why different learning mechanisms have different characteristics, and we should expect to obtain answers in terms of their survival and reproductive value. The same mechanism that is well designed to help us learn whether a potential food is healthful or poisonous, based on the aftereffect of eating it, is not well designed to help us learn whether a new word should be treated as a verb or a noun. The evolutionary perspective provides us and our students with a powerful tool for understanding and thinking about all processes of learning.

When humans are compared to other species, discuss the evolutionary rationale for the comparison.

Knowledge of evolution helps students understand and appreciate psychological research with non-human animals. From an evolutionary perspective, two kinds of similarities can exist across species. Homologies are similarities due to common ancestry, and analogies are similarities due to convergent evolution. Homologies necessarily involve common underlying mechanisms, but analogies do not. Psychologists who wish to learn about mechanisms of human behavior by studying other animals usually focus on characteristics that are homologous to those in humans.

Analogies are of less value in the study of mechanisms, but they provide clues about ultimate function. Species that are analogous in some characteristic can be compared to see what other characteristics they share or what environmental pressures they face in common, to test theories about the value of that characteristic.

In his Nobel lecture, Konrad Lorenz (1974) contended that his main contribution was to clarify the distinction between homologies and analogies in behavior and to show the different values of studying each. I have found that sharing Lorenz’s insight with students helps them overcome their confusion as to how and what psychologists can learn about humans through studying other species.

Use the evolutionary perspective to foster critical thinking.

All of the just -described applications of evolutionary theory involve critical thinking. They all ask students to generate evolutionarily plausible answers to “why” questions.

A Final Word of Advice

If you haven’t previously employed the evolutionary perspective in your course, start gradually. Make students aware of the perspective and apply it in ways with which you feel most comfortable. If it works, go a little further next time you teach the course. Don’t use the perspective in ways that seem artificial or strained to you; in that case they will certainly seem so to students. This approach has worked well for me, and I believe it will improve the academic survival of both you and your students.