Monday, September 1, 2008

Evolutionary Psychology: A Conceptual History


Humans are curious creatures. Our curiosity is a characteristic we share with other primates and is a primary reason for our evolutionary success. It is also the basis for the natural sciences, including evolutionary psychology: the study of human behavior from an evolutionary perspective. The goal of evolutionary psychology is to understand both what we do and why we do it.

Evolutionary psychology is a synthetic science, uniting the empirical study of human and primate behavior with a theoretical analysis of the evolutionary dynamics by which such behavior has come about. It differs from European psychoanalytic theory, which historically focused on inferring internal motivational states grounded in basic drives such as hunger, fear, and sexuality. It also differs from American behavioral psychology, which focused on behavior without reference to internal motivations or intentions.


People are curious about people. We have always been fascinated by what people do and why we do it. Most people are compulsive “people watchers”, beginning in very early infancy and lasting the rest of our lives. We are endlessly attracted to other people, constantly watching them and trying to figure them out. And not just other people: we carefully observe our own behavior, interpreting and anticipating our own actions as avidly as those of the people around us. This curiosity about each other and ourselves is a trait we share with other social animals, especially primates. As we will see, this exaggerated curiosity is not accidental, nor is it necessarily bad. On the contrary, it is one of the central reasons for our success, as individuals and as a species. Curiosity may have killed the cat, but it has more than once saved the lives of our evolutionary ancestors.

This series is about the reasons why we are so curious about each other, and what we have learned so far as the result of satisfying that curiosity. The subject of the science of evolutionary psychology is us, and its primary goal is to understand what we do and why we do it. Put in formal terms:
Evolutionary psychology is the scientific study of human behavior from an evolutionary perspective.

Evolutionary psychologists observe people very carefully, either directly or by analyzing indirect information such as demographic data. Our work sometimes takes us into the field, observing people in their “natural habitat,” in much the same way that an ornithologist might observe the behavior of an exotic bird. Some evolutionary psychologists also conduct carefully controlled laboratory experiments, although the “laboratory” may be something as simple as a rickety bridge across a gorge on a college campus. In both cases, the intent is to observe people in the same way that animal behaviorists observe members of other species: without biases or preconceptions about what ought to be happening.

Evolutionary psychologists also ask people what they are doing and why they are doing it, although as we will see, such self-reporting is often unreliable. This isn’t necessarily bad; even such unreliability can tell us something interesting about human motivations and our capacity for self-deception.

Evolutionary psychology is a branch of psychology, one of the newest branches of one of the oldest of human disciplines. As the name implies, it has its roots in Charles Darwin’s theory of evolution by natural selection. Darwin’s theory gives us a theoretical perspective that makes it possible to ask questions about human behavior that have not been asked in a systematic way before. It also provides a very practical set of experimental and observational techniques that allows us to make predictions about human behavior in specific contexts.

What evolutionary psychology does not do is recycle old ideas about human nature, except insofar as such ideas may coincidentally be based on the unbiased observation of human behavior. Evolutionary psychology is most emphatically not social Darwinism, neither in its origins nor in its conclusions. Indeed, I hope you will be surprised at some of the concepts that have come from the scientific study of human behavior from an evolutionary perspective.

Two Approaches to Psychology

Again, evolutionary psychology is about what we do and why we do it. Psychologists have historically focused on one of these two subjects, often to the exclusion of the other. That is, psychologists have often either focused on external behavior or its internal motivation:
Behavior is what an organism does,


Motivation is why an organism does it.

Although this division appears simple, it encapsulates a dichotomy that has split psychology into two often hostile camps for over a century. Essentially, this division is between experimental psychologists who believe that only observable phenomena can be studied using scientific methods, and theoretical psychologists who believe that it is not only possible to infer and thereby study internal motivations and mental states – that is, the “mind” – but that such internal states are the “ultimate” causes of observable behavior.

As we will see, this division is often mirrored in evolutionary biology. On one side are the field and laboratory scientists who conduct carefully controlled observations and experiments testing relatively limited hypotheses. On the other are theoreticians who use mathematical and computer models to formulate synthetic theories that are not always amenable to direct empirical testing.

Does this mean that these divisions are therefore unbridgeable? If history is any guide, the answer is “no.” In the Origin of Species, Darwin presented a synthetic theory of evolution, in which field and laboratory observations are used as a foundation for inferring an overarching explanation of the causes and consequences of what Darwin called “descent with modification.” Darwin not only presented mountains of evidence showing that evolution had happened, he also provided a testable explanation of the mechanisms that had caused it, an explanation based solely on naturalistic processes.

Evolutionary psychology, like evolutionary theory in general, aims for a synthetic theory that includes both rigorous and unbiased observations of human behavior (including an examination of the contexts within which behaviors occur) and an explanation of the underlying causes of those behaviors from the perspective of evolutionary biology. As such, it constitutes what may be the first genuinely unified theory of human behavior, one that is both grounded in direct observation, yet applicable to the many of the most abstract levels of human cognition – such things as epistemology, ethics, and even aesthetics.

Many of the explanatory concepts developed by evolutionary psychologists have come from relatively simple observations of people in partially or fully controlled environments – the same kinds of observations made by social psychologists and sociologists, although from a somewhat different perspective. Other concepts have come from answers to questions posed during interviews or on questionnaires. Still others have come from analysis of census data or demographic data collected for other purposes.

Some explanatory concepts in evolutionary psychology are derived from general evolutionary theory – that is, from the formal theories of evolutionary biology, abstracted from specific cases. For example, much of what evolutionary biologists have learned about sexual behavior and mating has come from observations that were stimulated by theoretical analyses of the effects of differing amounts of parental investment in offspring. As has often been the case, such abstract theories have suggested empirical tests, which have yielded many interesting (and often surprising) observations and inferences, which have in turn suggested new theoretical analyses.

Finally, some explanatory concepts in evolutionary psychology have come from studies of other non-human animals. This strikes some people (and especially some social scientists and humanists) as odd and perhaps leading to invalid conclusions. After all, people are very different from other animals in many respects. While this is true, it ignores a central concept of the natural sciences:

Similar causes produce similar effects.

In other words, comparative studies of the behavior of other animals in particular contexts can provide remarkable insight into the causes of such behavior. If such causes and contexts also apply to human behavior, then we may infer that similar causes and contexts can indeed be correlated with similar effects.

What does this allow us to do? When it works, it allows us to predict the future. This is the underlying goal of all scientific investigation: to understand enough about the causes of natural phenomena to be able to predict – that is anticipate – their effects. And, of course, to satisfy our curiosity…because that is why we are so curious in the first place. Curiosity, like so many other human (and primate) behavioral traits, has adaptive value. Or, as restated in the parlance of evolutionary biology:
Individuals who are curious about the behaviors and motivations of others survive and reproduce more often than those who are less curious.

A Brief Conceptual History of Psychology

Psychology as a science is relatively new, compared with many of the other sciences. However, trying to figure out the patterns of human behavior and the reasons for those behaviors predates the origins of civilization:

• There are records from Egyptian papyri that indicate that almost four thousand years ago people were thinking about the causes of such psychological conditions as clinical depression.

• The Dead Sea Scrolls, dating to about 100 years B.C.E., include a description of two different temperaments in humans, an early attempt to find a pattern in the motivations of human behavior.

• In China, psychological tests have been part of civil service examinations for centuries.

The term “psychology” was first used in its modern sense in 1590 by the German philosopher Rudolph Goclenius, who based it on the Greek word psyche, meaning “soul” or “spirit.” From this viewpoint, “psychology” means “knowledge or understanding of the human soul or spirit.” European philosophers and theologians had speculated for millennia on the existence and properties of the “soul”, but in 1672 Thomas Willis asserted that the “soul” is a function of the human brain, rather than the heart or some immaterial entity.

Psychology as a science can be dated to 1879, when Wilhelm Wundt founded a laboratory in Leipzig, Germany to study human behavior and mental states. In 1890, the American educator and psychologist William James published the first edition of his textbook, Principles of Psychology. In it, James (like Wundt) asserted that human behavior could be analyzed using the methods of the other sciences, and that this is possible because human psychology is a natural phenomenon, rather than something supernatural like “souls”. Inspired at least in part by James’s work, American psychologists founded the American Psychological Association in 1892, basing its practices and philosophy on the experimental approach pioneered by Wundt and James.

However, the experimental approach favored by many American psychologists was soon overshadowed by the work of Sigmund Freud, an Austrian physician originally trained in medical neurology. Freud began his professional career using hypnotism to attempt to treat patients with psychological ailments, but moved on to propose a comprehensive theory to explain the underlying causes of human behaviors.

Freud’s theory of psychoanalysis was based on a unifying idea: that almost all of human behavior was ultimately motivated by unconscious “drives,” such as hunger, thirst, fear, and especially sexuality. Since in Freud’s theories, such drives are unconscious and exist within the “mind” of the individual, they cannot be observed directly at all. Instead, their existence can only be inferred, based on the behavior of the individual whose actions they are supposedly motivating. Furthermore, Freud and many of his followers did not generally attempt to determine if his theories about drives and their implications were supported by observable evidence.

During the 20th century, Freud’s theories about the causes of human behaviors dominated the science of psychology in Europe, but in America a very different tradition developed. Called “behaviorism,” the founders of this tradition rejected Freud’s theories about motivation and unconscious mind, and focused instead on behaviors: what animals (including people) do, rather than speculating on why they do it. Behaviorists such as Edward Thorndike, John B. Watson, and especially B. F. Skinner argued that a purely empirical science of behavior could be developed that could be used to predict (and even to shape) animal and human behavior, without speculating about motivations.

However, after a half century of experimental psychology focused almost exclusively on behavior it became increasingly obvious that a full understanding of animal, and especially human behavior required a “theory of mind” – that is, required some theoretical model of how the nervous system produced behaviors, and why specific behaviors were correlated with specific contexts.

This revolution in psychology took hold in four places: in linguistics, in computer sciences, in neurobiology, and in the study of animal behavior from an evolutionary perspective.

• In linguistics, Noam Chomsky developed a theory of “natural language” which had at its base the idea that human language has a universal “deep structure,” and that the capacity to learn language is therefore innate: all humans are born with the capacity to learn language, without having to be taught.

• In computer sciences, the development of information processing programs required a computational architecture that included something like a “mind;” that is, a central processor that integrated inputs (“sensations”) with outputs (“behaviors”).

• In neurobiology, investigations of the structure and function of the sensory, nervous, and motor systems of animals (including humans) pointed to a “functional architecture” that both facilitated behavior and constrained it within patterns set by the cellular architecture of the nervous system.

• In the study of animal behavior, empirical studies of how animals learned showed that the “pure” behaviorism of the American school did not explain why different species of animals (and indeed, different sexes and individuals within a species) exhibited different behaviors in specific contexts.

Two new disciplines within the science of psychology have grown out of these four traditions: cognitive psychology and evolutionary psychology. Both of these new disciplines are grounded in the use of the scientific method: they depend upon observations of behavior to infer theories of motivation, and reject introspection as a way of determining why an organism does what it does. And, unlike behaviorism, both disciplines also explicitly infer the existence of internal mental states.

Ultimately, I believe that the disciplines of cognitive psychology and evolutionary psychology will eventually merge into a synthetic discipline in which behavior and motivation are both explained with reference to the underlying architecture of the nervous system, within which the mind resides, and which is ultimately shaped by the evolutionary history of our nervous systems. This series is a first look at this evolving synthesis, and at the evidence upon which it is based.

Essential Reading:

Buss, D. (2004) Evolutionary Psychology: The New Science of the Mind,, chapter 1: “The Scientific Movements Leading to Evolutionary Psychology.”

Supplemental Reading:

Barkow, J., Cosmides, L., & Tooby, J. (1992) The Adapted Mind: Evolutionary Psychology and the Generation of Culture, chapter 1: “The Psychological Foundations of culture.”

Cosmides, L., & Tooby, J. (online) “Evolutionary Psychology: A Primer.”

Questions to Consider:

1. Why might curiosity have been adaptive to our evolutionary ancestors?

2. Before beginning this series, what part (if any) do you think evolution has played in human psychology?


As always, comments, criticisms, and suggestions are warmly welcomed!



DiscoveredJoys said...

I am looking forward to your later blog posts because they are interesting and useful to me. I am writing a book (in fiction format) which explores the interactions between wisdom, happiness, meaning of life and our evolutionary roots.

I guess you can easily infer that I believe that our evolutionary past has a direct bearing on our psychological present. In addition it is not too much of a just-so-story to expect that the ability to detect and analyse the behaviour of other agents, particularly those in our social group, would be an adaptive behaviour.

I recommend "Philosophy in the flesh" by Lakoff and Johnson as an interesting challenge to analytical philosophy, since it is based on the major findings of cognitive science:
1) The mind is inherently embodied
2) Thought is mostly unconscious
3) Abstract concepts are largely metaphorical

Although I think their approach is too philosophical, nevertheless it explains a great deal of our behaviour using only biological (embodied) processes - no soul or trancendental essence involved.

I rather suspect we would have markedly different minds (if we had minds at all) if our species was made up of solitary carnivores, or of herd herbivores.

If only we had a similar work addressing how the embodied mind works when surrounded by a troop of similar primate omnivores with a longish evolutionary history...

Clint said...

Regarding determinism in Psychology/Social Sciences, my article “Determinism and the Antiquated Deontology of the Social Sciences” might be of interest:

It basically argues that the common gut-level reaction in the psychology/social sciences to anything deemed “deterministic” is overly simplistic and out of touch with the last half century of important developments concerning free will and ethics in philosophy.

Clint said...

Oops - the long URL did not fit above, so here is a shorter URL link:

Gretchen said...

You wrote that theoretical psychologists believe that internal motivations and mental states are the "ultimate" causes of observable behavior.

I believe it is true that human perception and motivation are a function of human behavior. Only until a human can objectively study their own perceptions and motivations versus "what is" will man evolve to another level.

It seems we are struggling to determine our "ultimate" beginnings as did our evolutionary ancestors. Their curiosity led to the creation of various gods and religion. Psychology has tried to study this phenomenon - Thomas Willis being one who considered the soul as "a function of the human brain." One important question arises to which many would like an answer: Is there a soul or is it just the mind at work?

teresa said...

Hello, I am a medical doc who loves evolutionary Biology and a number of other things. I've read some of your posts with interest. In fact I was a big fan of S.J. Gould and in 1992 or thereabouts, I heard him lecture at Cornell!

I love 50's and 60's pop culture, and one of my hobbies is collecting vintage Barbie dolls from that era. I have a blog in which I wrote an essay relating Barbie's evolution to biology (neoteny) a la Gould's
"Homage to Mickey Mouse". I wonder if anyone might be interested in reading it? (Barbie fans themselves tend to be highly visual creatures, and do not like to read excessively.)

The link is

Thanks, and my compliments to this site,
Teresa Brandt