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The Roots of Evolutionary Psychology Evolution and Theories of Behaviour: From Darwin to Evolutionary Psychology
Author Paul Kenyon
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Charles Darwin
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Konrad Lorenz

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Niko Tinbergen

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James Watson
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E.O. Wilson
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Early views on evolution
If you look at a school of fish, field of corn or flock of birds, you may be struck by the similarity between members of the same species. One sparrow is pretty much like any other sparrow and a randomly selected individual could be used to illustrate a type or species. This is the way most people viewed plants and animals until Darwin drew attention to subtle individual differences within species. This is most apparent in a species we are very familiar with - humans - we can easily distinguish between thousands of people we meet over a lifetime.
But the same is true of other animals. Farmers recognize individual cows and sheep in their care, and ornithologists are able to distinguish between birds by variation in their plumage.

This picture shows how. Notice that each individual cow has a unique set of markings. Once it is pointed out this is obvious, but what is its significance? Variation extends beyond surface characteristics. Variation can be found throughout animal biology and behaviour. Darwin realized that variation was like 'grit in an oyster' - it provides opportunity for development and change.

Darwin's theory of evolution by natural selection

Darwin's theory of evolution involving natural selection based on variation led to a gradual abandonment of Greek typological (types) thinking which viewed species as static and unchanging.

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This lecture does not discuss evidence that evolution has occurred (e.g. the fossil record, domestication etc.), but if you are interested here is a video of a lecture given by Paul Taylor ("Fossils: Extinction and Evolution") who works in the Natural History Museum in London.

It is agreed by scientists that species that now exist originate from very simple forms of life that existed millions of years ago. There is no scientific evidence to dispute this claim. Darwin successfully demonstrated that evolution has occurred, and he gave us important insights into how evolution occurs.

According to Darwin:

  • organisms show variation in almost every aspect of their biology and behaviour
  • variation is inherited - it is passed down from parents to offspring
  • inherited variation affects survival and reproduction
  • this mechanism is called natural selection

Here is a lecture by Richard Dawkins on natural selection.

Darwin: Cultural and historical multimedia materials
  • origin-fronspiece.jpg (10355 bytes)View the PBS video (if necessary, borrow headphones from technicians office) Evolving Ideas: Who Was Charles Darwin? which "... highlights Charles Darwin's personal struggle to bring to light his theory of evolution through natural selection, which meant going against societal norms of the time. In this brief portrait, students will discover how his upbringing, curiosity, and passion for natural history, his voyage on the Beagle, and his reliance on scientific process led to the publication of his groundbreaking book, On the Origin of Species by Means of Natural Selection." and consider the following points:
    • What was Darwin's job on H.M.S. Beagle?
    • Where did Darwin collect the specimens that gave rise to his theory of evolution? Would such a trip be funded by today's research councils? - Are blind men funded?
    • What scientific technique did Darwin employ?
    • How was the appearance of species explained before Darwin?
    • Why was Darwin reluctant to discuss and publish his theory?
    • What is the message for contemporary psychologists in Darwin's story?
    • What is the significance of the diagram Darwin is shown drawing towards the end of the video?
  • Listen to the PBS audio interview with James Moore in which he discusses Darwin and Victorian Culture and consider the following points:
    • What was the status of 'creationism' in Victorian society and what is its position today?
    • What was the position of 'transmutation' in Victorian society?
    • How was the publication of Darwin's book "The Origin of Species" greeted by the critics?
    • What did the study of geology contribute to Darwin's thoughts about evolution?
  • View the PBS video Darwin and Malthus, and read this brief online description of the impact of Malthus on Darwin's thinking. Consider the following points:
    • Outline the social condition of the poor in Victorian England.
    • What was the influence of Malthus' views on the growth of populations on Darwin's view of natural selection?
    • Compare Darwin's and Malthus' explanations for famine and poverty.
  • View the PBS video Darwin: Reluctant Rebel in which "James Moore explains that Darwin developed his theory of evolution by natural selection at a time when creationism dominated the public thinking. In this clip, Darwin is seen arguing for his theory with creationist thinkers, including the H.M.S. Beagle's Captain FitzRoy, his colleagues, and even with his own wife Emma. Philosopher Daniel Dennett explains that humans naturally want to believe that there is some purpose to the universe, and prefer to think of themselves as "special," rather than just another species in the animal kingdom. "
    Consider the following points:
    • Give two explanations  for the existence of different species of finch  on the Galapagos islands
    • Why were Darwin's views on evolution unorthodox?
    • Are there limits to the topics that should be investigated by scientists today?
    • Why are Darwin's thoughts on evolution dangerous?
    • How did Darwin's views on evolution interfere with his home life?
  • View the PBS video Evolution of the Eye  in which zoologist Dan-Erik Nilsson demonstrates how the complex human eye could have evolved through natural selection acting on small variations. How could Darwin use this research to explain evolution to his wife?
  • View the Scientific American Frontiers video "Evolving Beaks:Darwin’s famous finches exemplify evolution in action, as each generation's average beak size correlates to seed size on the island of Daphne Major."

When Darwin published "The Origin of Species by Means of Natural Selection" in 1859 it was generally believed that offspring represented a 'blending' or mixing of characteristics possessed by their parents. Natural selection would not support the evolution of beneficial variations if parental characteristics were mixed in this way because variation would be halved in every generation.

mendel.jpg (5147 bytes)We now know from Mendel's work published in 1865 that heredity is particulate - parents pass on particles or packages of information ( genes) to their offspring. For example,  children inherit the eye color of a single parent. Children of a brown-eyed father and blue-eyed mother do not end up with an intermediate eye color. Darwin was not aware of Mendel's discoveries and he was troubled by how variation could be inherited.

mutation.jpg (12164 bytes)Mutation is an important source of genetic variation. Half the genes in our body come from our mother, half from our father. Mutation is an error that arises when genetic information is copied during the formation of sperm and eggs. Thus mutations may pass into the next generation. If the variation produced by the mutation enables the bearer to be more successful at surviving and reproducing, it will tend to spread through the population in succeeding generations.

View this PBS (2001) video 'A Mutation Story' which "...tells the story of a genetic mutation affecting the population of West Africa. Although helpful in preventing malaria, this mutation can also lead to sickle cell anemia. Sickle cell specialist Dr. Ronald Nagel stresses the genetic diversity required for the survival of a species."

Role of sexual selection

Darwin was struck by the fact that some animals seem to have characteristics that pose a serious threat to their survival. For example peacocks have elaborate plumage that would appear to make them conspicuous to predators and seriously hamper their ability to take flight. In a second book (The Descent of Man and Selection in Relation to Sex) published in 1871 Darwin suggested that such traits have reproductive advantages. Females may be more likely to mate with such males.

Thus two mechanisms were thought to contribute to evolution:

  • natural selection and
  • sexual selection

Impact of Darwin's theory on social and political life

Darwin's ideas were - and continue to be - controversial because they can be applied to humans as well as other animals.

This story is told of two victorian ladies in conversation. One says: 'Have you heard that Mr Darwin says we are all descended from an ape?' The other replies: 'Oh, my dear - that surely cannot be true! . . . But, if it should be true, let us pray that at least it will not become generally known!'

Social Darwinism was championed by the British philosopher Herbert Spencer who coined the phrase 'survival of the fittest' which implies that only the ruthless will survive.

spencer.jpg (4246 bytes)Boakes (1984) gives this summary of his views:

".. progress in society was to be achieved by a 'genuine liberalism' which maximized individual liberty and minimized interference from the State; vaccination, and care for the infirm or insane, only served to promote the regression of the human race; economic and social differences between races, sexes or classes were part of the natural order, a necessary part of evolution."

The British prime minister Margaret Thatcher seems to echo this philosophy when she declared that 'there is no such thing as society'

indian2.jpg (9402 bytes)Spencer's views were particularly popular in America after the Civil War where industrialists interpreted fitness as the generation of wealth, and military campaigns against Sioux and Comanche Indians could be justified in terms of the survival of one group of people at the expense of another.

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Boakes (1984) uses the term 'Psychological Darwinism' to describe the belief that there are significant psychological differences between groups of people due to differences in brain structure (neophrenology). Around the early years of the 20th Century British, German and American scientists who held similar views on the existence of racial types cited studies that measured human head shape and sizes as a way of differentiating between human races. These studies were conducted against a background of increasing opposition to immigration in the United states of America.

This 1891 cartoon expresses the views of those opposed to immigration into the USA.

The frock-coated politician is telling Uncle Sam that "If immigration was properly restricted you would no longer be troubled with anarchy, socialism, the Mafia, and such kindred evils!'" Captions on immigrants in the picture label them :Polish vagabond, Italian brigand, English convict, Russian anarchist, Irish pauper.

Here is a larger version of this cartoon

Students of racial types used the Cephalic Index in which the breadth of the head above the ears is expressed in percentage of its length from forehead to back. Assuming that this length is 100, the width is expressed as a fraction of it.

These photographs show three types of head from France. The cartoon contrasts the head shape of Florence Nightingale with a stereotyped (Irish?) immigrant Bridget McBruiser.

  As head becomes proportionately broader, more fully rounded, cephalic index increases. Narrow heads were favoured for immigration purposes. This map of the Cephalic Index in eastern Europe shows narrow heads in Sweden, near Baltic, and broader heads in Bosnia, Serbia and White Russia.


Here is a larger version of this picture

Here is a larger version of this drawing

Map created by Madison Grant, Chairman, New York Zoological Society; Trustee, American Museum of Natural History, "The Passing of the Great Race, or The Racial Basis of European History," 1918, p. 220 ff.

This racial map shows:

Nordics in pink,

Alpines in green,

Mediterranean's in yellow;

and has crosses for Cro-Magnon area in Southwestern France.

Here is a larger version of the map

boas.gif (5833 bytes)But this view of race and the call to curtail immigration was abandoned in America in the 1920's after the anthropologist Boas showed that racial differences were not stable: Children born to immigrant mothers did not display the racial characteristics of their parents. This is the beginning of the idea that as environmental conditions improve, differences between people become minimal. Although young anthropologists and sociologists were persuaded by Boas' findings to abandon notions of inherited racial differences, older psychologists, particularly those in senior academic positions, were more reluctant.

At this time psychology was a a new subject struggling for recognition as a respectable scientific discipline. Psychological Darwinists played a prominent role in utilizing intelligence tests to aid recruitment to the American army which was engaged in fighting the First World War in Europe. This was obviously prestigious work for an emerging discipline which could have made a major contributions to the nation's welfare.

Things came to a head in the 1920's when some American psychologists (who were mostly WASPs - White Anglo Saxon Protestants) attempted to use the results of IQ tests to influence congress which was debating the introduction of legislation to restrict immigration from southern and eastern Europe. This attempt to use psychology to influence legislation was opposed by scientists who had suffered from racial discrimination on account of their 'non-Aryan' background. But the influence of Psychological Darwinism and eugenics persisted - and had horrific consequences - in Europe

Eugenics has its roots in the work of Darwin's cousin, Francis Galton who, in 1869, suggested that society should encourage breeding among its 'talented members' and discourage it in 'imbeciles' and 'idiots'. Darwin was convinced by his argument writing "You have made a convert of an opponent .... I have always maintained that, excepting fools, men did not differ much in intellect, only in zeal and hard work ..."

A trivial consequence of eugenics was the introduction of the first name Eugene. More seriously, in the USA some States had legislation to sterilize the 'feeble-minded'. Between 1907 and 1940, more than 35,000 involuntary sterilizations were carried out by the U.S. government on poor women, mostly in California (Platt 2002). In the words of one judge "three generations of imbeciles are enough" (Jones, 1993).

Similar views were expressed by the then British Home Secretary Winston Churchill who commented in 1910 that :

"The unnatural and increasingly rapid growth of the feeble-minded and insane classes, ..... constitutes a national and race danger which is impossible to exaggerate" (Jones, 1993)

In Germany the influential embryologist Ernst Haeckel laid the intellectual foundations for sterilization, genocide and antiabortion laws when he suggested that "The lower races are psychologically nearer to the animals than to civilized Europeans. We must, therefore, assign a totally different value to their lives."

Under the 1933 Law for the Prevention of Genetically Diseased Offspring, the Third Reich compulsorily sterilized about 400,000 victims, broadly categorized as "socially unfit by virtue of defective biology" (Platt 2002).

The title of Hitler's biography, Mein Kampf (My Struggle) echoes Spencer's phrase 'the struggle for existence' and he was clearly influenced by eugenic ides when he wrote that

"Whoever is not bodily and spiritually healthy and worthy shall not have the right to pass on his suffering in the body of his children".

But Hitler was not the sole architect of the horrors that descended on Europe between 1939 and '45. According to Jones (1993) "Half of those at the Wannesee Conference, which decided on the final solution of the Jewish problem, had doctorates, mainly in anthropology."



The eugenics movement in Nazi Germany believed it was possible to 'improve' the human gene pool and embarked on a program of genocide and sterilization and selective breeding - During WW2, there was the bizarre SS operation known as Lebensborn - a breeding program to produce 'racially pure' children.

Although the popularity of eugenics waned in the USA in the 1920's, it persisted in Europe until the end of World War 2 when the full horrors of the concentration camps were exposed in newsreels across the world. But as late as 1988 the phrase "Idiots give birth to idiots" was used to justify restrictive marriage laws in China.

Although eugenics focussed on measuring physical attributes such as the size and shape of the head, it is clear that the racial characteristics targeted by eugenicists are behavioural, rather than purely physical. For example, the cartoon illustrating American objections to immigrants highlights behavioural (Polish vagabond, Italian brigand, English convict, Russian anarchist, Irish pauper), rather than physical characteristics.

Genetic engineering, the human genome project and eugenics in the 21st century

The following section is based on a newspaper article by Connor (2003) "James Watson Nobel Prize Winner. Welcome to the Watson Wonderland: DNA genius still ruffles feathers 50 years after extraordinary discovery". The Independent, Monday 3rd February, 2003 , p 11. available online

watson-crick-dna.jpg (54495 bytes)In an interview to mark the 50th anniversary of his co-discovery of DNA with Francis Crick, the 75 year old Nobel prize-winner James Watson, who is now president of the prestigious Cold Spring Harbor Laboratory in New York, added to his reputation for holding outrageous and politically incorrect views by making the following comments on eugenics:

  • "I always draw a laugh when I say that everyone knows the Irish need improvement:
  • "You know, the only people who say that stupid people don't exist are people who are not stupid. We know that if we go to homeless people there is an underclass with a very strong mental disease component. Those people can't pull themselves together, the brain just won't allow it. So it is not that they are weak in character, they are seriously unequal."
  • People in first-class universities may have brains that work more efficiently than people who aren't there and if you could help someone, wouldn't that be nice."
  • "It's almost impossible to study the genetics of intelligence either in the US or the UK because it is socially contentious. You can say that the net effect is that it helps to perpetuate a system where people are dumb."

Connor notes that the study of genetics is fraught with difficulty because it is linked with the eugenics movement of the 1920s and 1930s that led Hitler's concentration camps. In response Watson argues:

  • "Should Hitler harm us for the next 200 years by saying that we cannot do genetics? People say to me that 'you are acting like Hitler'. People have accused me of being a Nazi just because I won't accept raw evolution, because I wanted to filter it a little and try to improve the quality of life.... We can say that we want to improve human beings genetically but we don't want to do it by the ways that were attempted in the past."
  • Referring to the Human Genome Project, Watson comments "The book of the DNA sequence would in time be regarded as more relevant to human life than the Bible. It tells us who we are, I've never read the Bible, so I'm not sure I've missed much."

Founding fathers of ethology and behaviourism

Konrad Lorenz
Niko Tinbergen

In 1972 Lorenz and Tinbergen received the Nobel Prize for their work.

After the second world war there were two broad approaches to the study of animal behaviour in Europe and America.

The European school was founded in the 1930's by the Austrian Konrad Lorenz . He collaborated with the Dutch zoologist Niko Tinbergen to establish 'ethology' which he defined as the 'biological study of behaviour'. Tinbergen's book 'The Study of Instinct' remains the best introduction to the ethological approach to the study of animal behaviour.

The American approach to animal behaviour has its roots in the work of J.B. Watson who in 1924 laid the foundation for an experimental approach to the study of behaviour in his book 'Behaviourism'. Watson was influenced by Pavlov's work on classical conditioning, and the English philosopher John Locke who believed that we are born as a blank slate "tabula rasa" on to which we write the associations we perceive in our environment.

Watson's ideas were adopted by experimental psychologists who were particularly interested in studying learning under laboratory conditions. Perhaps the best known exponent of this approach in its purest form was Fred Skinner who believed that behaviour was shaped by reward. Essentially reward leads to the repetition of a behaviour.

Fred Skinner

The rat's behaviour is 'shaped' by giving a pellet of food delivered via a button in Skinner's hand.

Characteristics of ethology and comparative psychology

Ethologists are concerned with:
  • identifying and describing species-specific behaviours. These are behaviours that show little variability between members of the same species e.g. courtship displays in birds
  • understanding the evolutionary pathway through which the genetic basis for the behaviour came about.
  • Many ethologists capture their observations on videotape or audio tape. From their observations they make an ethogram: a description and documentation of the behavioural patterns under study, a behavioural inventory.
  • The first ethologists were European scientists (e.g. Lorenz, Tinbergen)
    • trained in zoology;
    • studied the evolution of behaviour;
    • in birds, fish and insects;
    • used field experiments and made observations of animal behaviour under natural conditions;
    • discovered species specific fixed action patterns elicited by sign stimuli acting through innate releasing mechanisms;
    • used the term instinct to explain motivation

Behaviourists and comparative psychologists were:
  • initially North American scientists,
  • trained in psychology,
  • rejected the notion of instinct
  • interested in the flexibility of behaviour shown by individuals rather than the evolution of behaviour in species, and
  • understanding the environmental requirements for the development of behaviour in the young;
  • Studied how we learn new behaviours,
  • using a restricted number of species, principally rats and pigeons,
  • under laboratory conditions, using statistical methods and carefully controlled experimental variables,
  • with the intention of discovering general laws of behaviour that could be applied to all species including humans.

Here is a summary of these very different approaches, interests and backgrounds:

Some characteristics of classical ethology and comparative psychology
Feature Classical ethology Comparative psychology
Geographical location Europe North America
Training Zoology Psychology
Typical subjects Birds, fish, insects Mammals, especially lab rats
Emphasis "Instinct", the study of the evolution of behaviour "Learning", the development of general theories of behaviour
Methods Careful observation, field experimentation Laboratory work, control of variables, statistical analysis

Tension between ethology and psychology

It is perhaps not surprising that ethologists and behaviourists would eventually clash over their very different approaches to recording, analysing and interpreting behaviour.

After all they were studying very different types of behaviour.

For example, whilst ethologists were observing courtship displays in the field, psychologists were poring over cumulative records showing the impact of schedules of reinforcement on rates of bar-pressing in rats trained in Skinner boxes under carefully controlled laboratory conditions.

An extreme form of behaviourism - Radical Behaviourism held that:

One flash point between behaviourists and ethologists was interpretation of how behaviour develops.

According to Lorenz, species-specific behaviour develops without the animal experiencing the stimuli to which it responds, or without practice of the motor patterns that it performs.

Terms associated with this view that behaviour is the result of 'nature' include:

The American John Watson is credited with emphasizing the role of nurture in development. His view that we are born as a blank slate "tabula rasa" is captured by his famous claim:

"give me a dozen healthy infants, well -formed, and my own specified world to bring them up in and I'll guarantee to take anyone at random and train them to become any type of specialist I might select - doctor, lawyer, artist, merchant-chief, and, yes, even beggar man and thief , regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors" (see Boakes, 1984, pp226).

Watson was trying to develop a psychology that could be utilized by "the educator, the physician, the jurist and the business man ... in a practical way"

Terms associated with the view that behaviour is the result of 'nurture' include:

In his recent book "The Blank Slate: The Modern Denial of Human Nature", Steven Pinker (2002) points out the social impact of this type of thinking

"The Blank Slate has also served as a sacred scripture for political and ethical beliefs. According to the doctrine, any differences we see among races, ethnic groups, sexes, and individuals come not from differences in their innate constitution but from differences in their experiences. Change the experiences—by reforming parenting, education, the media, and social rewards— and you can change the person. Underachievement, poverty, and antisocial behavior can be ameliorated; indeed, it is irresponsible not to do so. "

Nowadays most psychologists accept that behaviour develops as an interaction between factors in an animal's environment, as well as biological predispositions. It is worthwhile examining some of the evidence that laid the foundation for this synthesis.

Maturation and practice of pecking by chicks
The development of pecking in newly hatched chicks is an example of the interaction between maturation (nature) and practice (nurture) in the development of a behaviour. Newly hatched chicks have an inherited tendency to peck at objects which contrast with their background, at first their aim is poor but it does improve. Cruze studied how this improvement occurs. He measured pecking accuracy by testing chicks individually in a small arena with a black floor onto which he scattered several grains of millet. Each chick was allowed 25 pecks; each peck was scored as a hit or miss.

Experimental design:

The experiment involved nine independent groups of chicks:


Conclusion: pecking improves as a consequence of both maturation and practice.

Point to ponder
What are the implications of these results for human development?

Limits to behaviourism: Preparedness and taste aversion learning

Behaviourists such as Skinner gave the impression that it was possible to condition any response that an animal could perform. However, the idea that through the process of operant conditioning, any reinforcer should be equally effective in increasing the frequency of any response was soon in serious doubt.

For example, although it is fairly easy to train a rat to run in a wheel to avoid shock, it proved impossible to condition a rat to rear (stand upright) to avoid the aversive stimulus. Seligman argued that evolution had prepared animals to make certain associations more easily than others. Thus rats are 'prepared' to run, but not to stand on their back legs, to avoid or escape from an unpleasant stimulus (data redrawn from Bolles, 1973)

In a famous experiment Harlow raised infant rhesus monkeys in isolation from their mother. They were provided with two 'surrogate mothers'

Harlow found that the infants spent most of their time clinging to the soft terrycloth-covered monkey even though it was not the source of food reinforcement.

Garcia and Koelling (1966) carried out an experiment on taste aversion learning involving 'bright noisy water' and illness induced by exposure to X-radiation. The training and testing conditions in their experiment are described in this table.

Training conditions Testing conditions Consequences Association learned?
Rats trained to drink water from a spout that caused a flash of light and a click when the rat's tongue touched to spout - 'bright noisy water' Made sick by X-radiation after drinking Offered 'bright noisy water' Drink normally
Given electric shock after drinking Offered 'bright noisy water' Fail to drink
Rats trained to drink water sweetened with saccharine Made sick by X-radiation after drinking Offered water sweetened with saccharine Fail to drink
Given electric shock after drinking Offered water sweetened with saccharine Drink normally

The results show that rats did form an association between

But, rats did not form an association between

According to traditional behaviourists, all the groups of rats should have learned an association between drinking from the spout and the aversive consequences, and should not have drunk under the test conditions. Therefore, Garcia's results challenge the idea that any reinforcer is equally effective in increasing the frequency of any response

Problems with viewing behaviour as either nature or nurture

According to the protagonists, behaviour can be divided into two types
Instinctive (innate, inherited) Learned (acquired)
  • Genes are inherited, but behavioural patterns per se are not inherited
  • Genes do affect behaviour, but all animals develop within some sort of environment (e.g. an animal's mother provides an environment before birth)
  • The 'sameness' of behaviour between members of the same species does not exclude the possibility that all members of a particular species share common learning experiences
  • Deprivation experiments (in which animals are raised in social isolation to remove environmental influences), have been criticized because:
    • the "deprived" environment is still an environment
    • learning can still take place in the deprived environments
  • It is logically impossible to test whether behaviour would develop the same in all environments
  • Learning is a process that changes pre-existing behaviour, therefore we get into a 'chicken and egg' situation. Where does this pre-existing behaviour come from - it cannot be learned!
  • Studies of preparedness and learning predispositions (e.g. taste aversion studies with "bright noisy" water) contradict the idea that through the process of reward and punishment, any stimulus can come to be associated with any response
    • Simple "nature/nurture" or "instinctive/learned" dichotomies have now been abandoned
    • All behaviour depends on both genes and environment
    • Attention is now focussed on experimental investigation of what does, or does not, influence behavioural development
    • Nowadays ethologists and psychologists are less divided by the nature - nurture debate. Both groups are interested in how genetic and environmental factors interact to control the development and expression of behaviour. In turn an individual's behaviour and environment feedback into the organism to determine its future behaviour.

The interaction between nature and nurture in the development of behaviour is similar to the path taken by the ball in a pinball machine.

The paddles and traps on the floor of the machine correspond to the environment in which the animal develops. The ball and firing mechanism correspond to the animals genetic endowment.

The path taken by the ball models how the animal's behaviour develops. The path depends on obstacles encountered as the ball moves around the environment.

The effect of obstacles will vary according to the nature of the ball - a hard ball will react differently to a softer one. Two identical balls launched with equal force will behave have an identical path around the machine. But if the environment is changed - for example, by removing one of the obstacles - then the pathway may be dramatically different.

In this way the environment plays an essential role in how genetically identical organisms will develop.


Point to ponder
Can you think of any recent debates about the causes of human behaviour which have been influenced by the nature - nurture debate? Can you classify the participants as taking a 'nature' or 'nurture' or 'interactions' view of human behaviour?

The Birth of Sociobiology and Evolutionary Psychology

Even though this lecture started off with a discussion of Darwin's theory, evolution has not been mentioned for some time. The debate between ethologists and behaviourists focussed on animal behaviour, and was conducted in scientific papers and conferences well away from public attention. Indeed the general public may have felt that - whereas the structure of the body was subject to evolutionary pressures - human behaviour was independent of evolution. This is reflected by the place of evolutionary theory in psychology. For many years it simply wasn't mentioned. Psychology textbooks in the period 1960-1990 gave little attention to the role of natural and sexual selection in the evolution of human behaviour.

But things are rapidly changing. 1975 E.O. Wilson wrote a groundbreaking and challenging book ' Sociobiology the New Synthesis ' in which he argued that human social behaviour could be explained in evolutionary terms. This caused an outcry in many quarters. Alcock (1998) provides a useful summary of the debate.

eowilson.jpg (6027 bytes)

Principles of Evolutionary Psychology

Cosmides and Tooby describe several principles that guide an evolutionary psychology approach to any topic within psychology:

  1. Modern skulls house a stone age mind." This is a catchy way of conveying the idea that human evolution occurred in a very different environment to the one in which we now live. Humans evolution is thought to have started 6-8 million years when we diverged from our primate ancestors. Evolutionary psychologists believe that natural selection designed our minds for life in an environment resembling the African savannah , in which our hunter-gatherer ancestors lived for thousands of years. For 99% of our evolutionary history we probably lived in hunter-gatherer societies. It is only about 10,000 years since humans first started growing their own food. The technical term used to refer to the environment in which we evolved is the Environment of Evolutionary Adaptedness EEA) . The EEA does not refer to some short period of time in our past. It refers to an array of factors that have influenced inclusive fitness during our evolution over the last 200,000 years. See Daly & Wilson (1999) for a very good discussion of this important distinction.
    The EEA may have involved (Badcock, 2000):

    food obtained via hunting / gathering /scavenging

  2. The human brain consists of neural circuits designed by natural selection to solve problems that our ancestors faced during our evolutionary history. Our mind consists of a collection of adaptations. Each individual adaptation has evolved to meet challenges in the environment, challenges faced in our EEA.
  3. Most of what goes on in the mind is unconscious . Most problems that we think are easy to solve are in fact very difficult to solve and require complicated neural circuitry. Consider vision, vision appears easy - open your eyes and you see the world - but this apparent simplicity hides a complex evolved system that we have not been able to reproduce artificially.
  4. Different neural circuits are specialized for solving different adaptive problems. An adaptation is

    "a characteristic that has arisen through and been shaped by natural and or sexual selection. It regularly develops in members of the same species because it helped to solve problems of survival and reproduction in the evolutionary ancestry of the organism. Consequently it can be expected to have a genetic basis ensuring that the adaptation is passed through the generations." (Williams, 1966)

    Evolutionary psychology views the mind as consisting of specialized modules that have evolved with the purpose of coping with adaptive problems. In contrast, psychologists have tended to view the mind as consisting of general purpose circuits involved in many different behaviours e.g. learning, intelligence, memory, reasoning, decision-making. You can see this approach reflected in the way your degree programme is broken down into modules covering these topics.

The overarching concern of evolutionary psychology is to identify factors that maximize reproductive success .

Evolutionary psychologists are particularly interested in psychological mechanisms that:

Eibl-Eibesfeldt took these pictures of a Himba woman from Namibia (SW-Africa). She shows a rapid brow raising (between the second and third still images) which coincides with raising her eyelids. Because all the cultures he examined showed this behaviour, Eibl-Eibesfeldt concluded that it was a human 'universal' or Fixed Action Pattern. How do you think this behaviour is related to reproductive success?

eyebrow-flash eyebrow-flash eyebrow-flash eyebrow-flash eyebrow-flash

The debate between the Standard Social Science Model (SSSM) and Evolutionary Psychology (EP)

According to some evolutionary psychologists (e.g. Cosmides and Tooby) the Standard Social Science Model (SSSM) is the prevailing orthodoxy in anthropology, sociology, and has dominated psychology since the 1920's.The SSSM is under challenge from Evolutionary Psychology (EP) which has mounted a critique of contemporary psychology because it has largely ignored the role of evolution in shaping human behaviour.

According to the SSSM: According to EP:
Body structure (e.g. hands, kidneys, eyes) has evolved Body structure (e.g. hands, kidneys, eyes) has evolved
There are several types of scientific endeavour e.g. natural sciences (biology, botany, zoology etc.); social sciences (sociology, psychology, politics etc.) All science is a single coherent entity consisting of many disciplines e.g. physics, biology, psychology, sociology etc. - all characterized by adoption of the scientific method.
Psychology is a social science. Social sciences are concerned with how culture and experience produce wide variation in human behaviour. Therefore social sciences do not need to consider the role of evolution in the development of behavioural variability. Biology is a natural science. Biology is built upon the rock of evolutionary theory. Psychology is a branch of biology.
Animal behaviour is controlled by their biology. Human behaviour is determined by culture and experience. Animal behaviour is more appropriately studied by biologists. Animal and human behaviour are biological phenomena that have evolved.

Ignorance of evolutionary theory can lead some psychologists to appear to view humans as having progressed to be above apes and other 'lower' animals on a 'scale of nature' or scala naturae.

Humans are born with a few reflexes and the ability to learn. Essentially we are 'empty computers' or 'blank slates' at birth, written on by the hand of culture and experience.

Fodor (1998) expresses this idea as follows:

"Most cognitive scientists still work in a tradition of empiricism and associationism whose main tenets haven't changed much since Locke and Hume. The human mind is a blank slate at birth. Experience writes on the slate, and association extracts and extrapolates whatever trends there are in the record that experience leaves. The structure of the mind is thus an image, made a posteriori, of the statistical regularities in the world in which it finds itself. I would guess that quite a substantial majority of cognitive scientists believe something of this sort; so deeply, indeed, that many hardly notice that they do."


The human mind consists of specialized modules that are innate and have evolved via natural and sexual selection to cope with adaptive problems. Modules resemble debugged computer programs designed for a particular process e.g. word processor, spreadsheet, database.

Fodor (1998) writes that evolutionary psychologists view

"..the mind as computational system; the mind is massively modular; a lot of mental structure, including a lot of cognitive structure, is innate; a lot of mental structure, including a lot of cognitive structure, is an evolutionary adaptation - in particular, the function of a creature's nervous system is to abet the propagation of its genome (its selfish gene, as one says)."

Human behaviour is controlled by a general purpose systems which rely on imitation, general intelligence, culture, reward and punishment. These systems are content-independent or domain-general. Modules are specialized to solve particular adaptive problems: For example, mate selection, language, social co-operation.
Human behaviour is acquired during the lifetime of the individual. Modules are inherited from ancestors who adapted to the EEA. The individual's internal and external environment plays a role in the expression of modules. Rather like setting the preferences for a computer program.
Culture determines what is learnt. Culture is a product of specialized modules. For example a page of text is the product of a word processing program.
We can arrive at a conscious decision about the best solution to many everyday problems. Many of the reasons for our behaviour are unconscious


Problems for Evolutionary Psychology (EP)

Some behaviours do not appear to be adaptive:

EP has been criticized for its methodology which is very similar to that used by Darwin. Darwin argued that no single experiment or observation would prove natural selection. He gathered a wide variety of different types of evidence and argued that they could all be explained by natural selection. In other words various pieces of evidence converged to support natural selection.

A similar approach is used by EP which relies on data from the following sources (see Buss (1999):

Just like Darwin they argue that data from these multiple sources converge to support the concepts developed by evolutionary psychology

Get-outs for Evolutionary Psychology

Evolutionary psychology is not ...


Ways of thinking about behaviour

One way of thinking about behavioural questions is to consider how they relate to stages on a species' journey through time, from the distant past into the future.

  • The evolution question: How has a behaviour evolved in the species? Is it shown by closely related species?
  • The development question: How does a behaviour develop during the individual's lifetime? Does the individual learn the behaviour? Does s(he) practice the behaviour? Is the behaviour performed perfectly the first time it is performed?
  • The cause question: What causes the particular behaviour? Are there internal factors (e.g. hormones) that influence the behaviour?
  • The function question: Why is the behaviour performed in a particular way? How do the behaviour contribute to the reproductive success of the individual, and ultimately the survival of the species?


PSY364 Evolutionary Psychobiology Seminar discussion themes

"Nothing in biology makes sense except in the light of evolution." Theodosius Dobzhansky, Geneticist.  Does anything in psychology make sense in the dark?

  • What is your position on the statement "If the human eye is an adaptation--that is, something functionally effective that has evolved through natural selection--then so essentially is the human mind" Hayashi (1999).
  • What is your position on the statements:
    • "People come pre-formatted, with cognitive organizing principles already embedded in their hardware."
    • I think ... that biology does in fact tell us that there is no inherent meaning to our lives.
      Barash (2002)
  • Is our behaviour open to introspection?

    What is your position on the following statements made by Stotz and Griffiths (2001) Dancing in the Dark: Evolutionary Psychology and the Argument from Design.

    • The SSSM " was the child of the 1960s, representing a politically motivated insistence on the possibility of changing social arrangements such as gender roles"
    • "Without an evolutionary perspective, psychological science is groping in the dark. It does not know what it is looking for and when it finds something it does not know what it is looking at."
    • "sociobiology was superior to ethology because it made predictions about behavior and tested them rather than merely describing behavior and explaining it."
    • "One of the best-known aspects of Narrow Evolutionary Psychology is the ‘massive modularity thesis’, according to which the mind has few if any domain general cognitive mechanisms. Instead, the mind is a collection of separate ‘modules’ each designed to solve a specific adaptive problem, such as mate-recognition or the enforcement of female sexual fidelity."
    • "What Narrow Evolutionary psychologists propose to do is more like a paleontologist who has found fossil birds with no skulls and proposes to reconstruct their feeding mode by thinking about the niche they occupied."
    • According to Lorenz " the units of behavior studied by behavior analysis in the first half of the twentieth century were biologically meaningless and thus not a useful guide to the principles according to which the mind works."
    • "The study of cognitive functioning can be illuminated by the causal functional analysis of the capacity of the mind to occupy its current niche."
    • "The real lesson which evolutionary theory has for psychology is that a synthesis is needed between behavioral ecology and developmental psychology - not evolutionary psychology, but evolutionary developmental psychology."
    • .."why did evolution invent complex and costly features like a mind and an extended period of post-natal development, while making no more use of them than to detect a few cues and respond with predetermined solutions to previously solved problems?"
  • Form your own opinions about the following questions after reading Carruthers (2002) Is the mind a system of modules shaped by natural selection?:
    • What does Carruthers mean by the terms 'module', encapsulated module', 'domain specific module', 'engineering kludges',?
    • Can evolutionary psychology account for flexibility in human behaviour?
    • How do desires arise?
    • Does the mind have a modular structure?
    • The sensory system has specialized modules for seeing, smelling, hearing, touch: Is the mind similarily broken down into modules for dealing with numbers, empathy, etc.?
    • Is the mind a product of natural selection, or is it created within each individual through general learning?
    • Would a 'general purpose learning system' be sufficiently efficient to have evolved?
    • Are the really important things that we need to learn below our 'cognitive radar'? I am using the term 'cognitive radar' to refer to factors that we are consciously aware of.
    • Is the human mind a 'computer without software programs'?
    • Could children do the things they do without a modular mind?
    • Are the effects of brain damage consistent with a modular mind?
    • How strong is the experimental evidence for modularity of mind?
    • Does modularisation emerge after general learning due to 'over-learning'? Why do we not meet otherwise normal people who have specific deficts in cognitive functioning?
    • What would be the role of a language module in a modular brain?
    • Is 'common sense' - Carruthers' practical reasoning - modular?
  • Do you think   political leanings have influenced adoption of evolutionary views about human behaviour?
    "It is, broadly speaking, true that the critics of evolutionary psychology are on the left politically. ... The supporters of evolutionary psychology are more widely spread politically, but share at least a folk memory of being oppressed by political correctness, after the early campaigns against them in the 70s. " from Brown, The Guardian,   Tuesday November 30, 1999 available online

Online resources


Copyright Dr. C.A.P. Kenyon 1994-2006