Evolutionary Psychology

Genes seem a matter a great deal in Psychology - they can shape our intelligence, personality, and abilities.  But where do these genes come from in the first place?  Why have we inherited a particular set of genes?  Answering these questions points to a larger story - the story of how evolution has shaped life on earth. 
Video Activity

Watch the video below on evolution by natural selection, and consider the following:

  • How does natural selection result in the evolution of a species?

  • Why do you think the giraffe evolved such a long neck?  Why do you think the cheetah evolved the ability to run at such a high speed?
Evolution by Natural Selection

As you saw in the video, the process of natural selection determines which genes get passed down to the next generation.  Over millions of years, evolution by natural selection has given rise to the astonishing complexity and variety of life we see today.  The giraffe has evolved such a long neck because longer-necked giraffes would find it easier to reach scarce food, and these longer-necked giraffes would then be more likely to survive and pass on their long-neck genes to the next generation of giraffes.  To summarize, the process of evolution by natural selection happens in the following five steps:

1. Genetic mutation - When DNA makes copies of itself through reproduction, the DNA code is not copied exactly - small errors occur.  Furthermore, because every animal (or person) receives half of their genes from each parent, the resulting offspring has a unique genetic blueprint.  Some of these mutations will be useful, increasing the odds of surviving and reproducing, while some will be harmful, increasing the odds of an early death.

2.  Competition for scarce resources - Imagine you went camping and got lost in the wild.  Would you be able to survive? For how long?  Before modern medicine, housing, and technology, simply staying alive was no easy feat.  You would have to constantly collect enough edible plants, or kill enough animals, while avoiding a multitude of dangerous animals and the force of storms, floods, and severe temperatures.  Staying alive required constant competition for limited food and other resources - both against other species and against other humans.

3.  Natural and sexual selection - Since staying alive in pre-modern times was difficult, only those humans with the "best" genes were able to survive and reproduce.  What counts as the "best" genes vary across different species and different environments.  For some animals, like the cheetah, it might be the ability to run fast and catch prey, while for others, it might be the ability to camouflage and hide from predators.  Because survival was so difficult, natural selection ensured that only "good" genes - those that increase the odds of survival - get passed down to the next generation.  Furthermore, in order to pass on your genes, it isn't enough just to survive - you also need to find a mate and make babies!  Competition for mates is often fierce - and so genes that increase the chances of attracting mates and successfully reproducing will be passed on, a process known as sexual selection.

4.  Differential reproduction - The forces of natural and sexual selection ensure that only those with "good genes" are able to survive, attract mates, and raise many healthy children.  On the other hand, those with "bad genes" may die an early death, fail to attract a mate, or have less numerous children.  Over many generations, those with "good genes" reproduce at higher rates, giving rise to more offspring who carry these genes, while those with "bad genes" reproduce at lower rates, resulting in the gradual disappearance of the "bad genes" from the population.

5.  Heritability of traits - Finally, the next generation inherits traits - transmitted through genes - that helped their ancestors survive and reproduce.  The long-necked giraffe that was able to reach enough plants in times of hunger passes on those long-neck genes to the next generation.  The reason you are alive today is because your ancestors - stretching back over millions of years - were somehow able to emerge victorious in the struggle to survive and reproduce, and they have passed on those winning genes to you.

All of these steps can be summarized in the diagram below:

Evolutionary Psychology

So far, we've been discussing evolution only in terms of physical characteristics - like the reason why giraffes evolved to have long necks, or why cheetahs evolved to run at high speeds.  What does have to do with Psychology?  The key link is that genes also influence how we think and behave.  Some behaviors increase the odds of survival and reproductoin, while other behaviors diminish the odds.  Therefore, genes that promote survival-enhancing behaviors tend to be passed down from one generation to the next.  A simple example can illustrate this - which of the following animals do you think you'd be frightened to meet in the wild?
Of course, the answer is easy - spiders, tarantulas, snakes and scorpions make us feel anxious, fearful, and eager to get away as quickly as possible.  And with good reason - these animals can be deadly.  Imagine that some early humans lacked the genes that made them fearful of these animals.  Such humans would be more likely to fall victim to poisonous bites or stings, and hence would die an early death, failing to pass on their genes.  On the other hand, those humans that ran away every time they saw a dangerous animal would have been more likely to survive (and thus reproduce).  We've inherited our fear of dangerous animals from those humans who were fortunate enough to be afraid (and run away) in the right moments.

The reason why we feel fear in some situations (and not others) can be traced to our evolutionary roots.  These days, far more people die in car accidents than die from tarantulas, yet we feel an instinctive fear towards tarantulas while gladly going for a ride in a friend's shiny new convertible.  Car accidents are a relatively new danger that our ancestors didn't have to confront, and so we haven't evolved a fear of cars.  Tarantulas, on the other hand, have lived alongside humans for millions of years - so we've had the time to evolve a fear of these animals.

For many more examples of how evolution may shape human behavior, take a look at the video below.

Try It Out

Can evolution explain why we find certain people (and not others) attractive?  The following activity will help you find out.

  • This website will allow you to create a "composite" face by averaging the faces of two or more people.  Try creating the most attractive man (or woman) you can by taking the average of two faces.

  • Now try to create the most attractive man (or woman) you can by taking the average of five (or more) faces.  What happens as you increase the number of averaged faces?  Why do you think this is happening?
Evolution of Attraction

The experience of falling for someone - feeling a magnetic urge to be with a certain person - has been the topic of countless songs, philosophical treatise, and works of literature.  What makes us feel attracted to someone?  Is it because of their wit, their kindness, their sense of humor?  Perhaps not entirely.  For evolutionary psychologists, attraction has evolved to serve a simple purpose - to help us choose a mate who will give us strong, healthy children with the best possible chance of survival. 

After all, in the bitter struggle to stay alive, only those with the best genes are able to reproduce and raise children successfully.  To ensure that your children have the best possible chance of survival, it is important to choose a mate who has healthy, adaptive genes.  If you mate with a person who has a genetic vulnerability to illness, or who has few resources, or who may die soon, then your children face a high likelihood of early death.  Just as fear evolved to keep us away from dangerous animals, attraction may have evolved to help us choose a mate with the best available genes.

The evolutionary explanation of attraction may help to explain why we tend to find composite faces (made by taking the average of many different faces) highly attractive.  If you compare a composite face to each of the individual faces, you will probably notice that the composite face has the following features:

  • Clear, blemish-free skin - Taking the average of many faces tends to cancel out any skin blemishes.  Clear skin is a sign of good health and lack of disease.  For early humans, living in primitive conditions with no antibiotics or cosmetics, clear skin signaled strong genes and resistance to infections and other diseases.

  • Facial symmetry - Composite faces tend to be highly symmetrical.  (If you draw a vertical line down the middle of the face, the two halves will be nearly exactly the same).  Just like clear skin, facial symmetry is also a sign of good health and strong genes.  Infections, wounds and health problems tend to make the face less symmetrical, so perfect facial symmetry signals strong health.

  • Perfect facial proportions - Composite faces tend to be perfectly proportioned - the eyes, ears, nose and so on are neither unusually large or small, rather everything seems "just right".  Perfect facial proportions may indicate a lack of genetic deformities and a good state of health.

To sum up, evolutionary psychologists regard attraction as a product of evolution - we have evolved to seek out mates with the best genes, so that our own children may survive and prosper.  Clear skin, facial symmetry, and perfect facial proportions all signal good health and strong genes, and that's why we find those features attractive.  For more on the evolution of attraction, take a look at the video below.

Think Critically

Do you find the evolutionary explanation of attraction to be entirely convincing?  If you said no, then you aren't alone.  For starters, people differ in what they consider attractive.  You might find consider a particular celebrity to be the hottest person ever, but your friends may have a completely different opinion.  Differences in what people find attractive are even greater across cultures - for example, for much of the last millennium in China, women with unnaturally small feet (a result of foot binding) were considered the most desirable.  This suggests that there is more to attraction than evolution alone.

In fact, much of evolutionary psychology has been subject to a number of criticisms, including the following:

  • Lack of experimental evidence - Although many evolutionary explanations seem to make sense, they are often very difficult to test experimentally.  For example, we can't be fully certain that the reason why people prefer "average" faces is because of evolution.  There may be other explanations (like culture) that we can't really rule out.

  • (Incorrectly) assumes that genes directly cause behavior - Evolutionary psychology is based on the assumption that genes are responsible for much of our behavior.  However, the relationship between genes and behavior is not so straightforward.  Even the simplest behavior is influenced by many hundreds, if not thousands, of genes.  Furthermore, as we saw earlier, genetic and environmental factors interact with each other to produce behavior.

  • Underestimates the role of culture in behavior - Ever wonder why many people in Western countries go to tanning salons to get darker skin, while many Asians will avoid sunlight in hopes of gaining a fairer complexion?  Clearly, culture plays a significant role in defining standards of beauty.  Evolutionary psychology tends to ascribe behavior to biological causes, underestimating the very significant role of culture.  For more examples of how far beauty standards vary across the world, watch the following video.

  • I can describe how genetic mutation, competition for scarce resources, natural / sexual selection, and the heritability of traits all play a role in the evolution of a species

  • I can explain why evolution plays an important role in how people think and behave

  • I can summarize the evolutionary explanation of human attraction, using the example of composite faces to explain why people are attracted to symmetrical, well proportioned and blemish-free faces

  • I can discuss some of the criticisms of evolutionary psychology
Quiz Yourself!

1.  Male peacocks with large, colorful tails are more likely to attract mates and succesfully reproduce.  This has caused male peacocks to evolve the splendid tails we see today.  This best illustrates the concept of:

(a) Genetic mutation

(b) Natural selection

(c) Sexual selection

(d) Survival of the fittest

2.  Which genes will be selected for by natural & sexual selection?

(a) Genes which enable an animal to survive the longest

(b) Genes which enable an animal to reproduce successfully

(c) Genes which increase the intelligence of an animal

(d) Genes which enable an animal to become bigger and stronger

3.  According to evolutionary psychologists, why are men attracted to women with a waist-to-hip ratio of around 0.7?

(a) Women with this waist-hip ratio are less likely to die in childbirth

(b) Women with this waist-hip ratio are less likely to suffer psychological disoders

(c) Women with this waist-hip ratio are considered beautiful in Western culture

(d) Women with this waist-hip ratio are over-represented in fashion magazines

4.  The "composite face" generator supports all of the following about human attraction, EXCEPT for...

(a) Symmetrical faces are judged to be more attractive

(b) Faces with clear, blemish-free skin are judged to be more attractive

(c) Faces with mathematically average features are judged to be attractive

(d) Faces that suggest exposure to the ideal level of hormones are judged to be attractive

5.  Which of the following is a key assumption of evolutionary psychology?

(a) Culture plays only a minimal role in shaping behavior

(b) Humans will continue evolving and will become smarter with each generation

(c) Humans no longer need to compete for scarce resources

(d) There is a strong correlation between genetics and certain behaviors

6.  Some argue that beauty is a social construct, defined by celebrities, beauty magazines, and other forms of media.  How might an evolutionary psychologist respond to this claim?

(a) Standards of beauty vary widely across different cultures

(b) Since the 1960's, Western media has equated beauty with thinness

(c) Beauty is in the eye of the beholder - we are all attracted to different people

(d) A cross-cultural study found that men around the world prefer the same waist-hip ratio


1 - C, 2 - B. 3 - A, 4 - D, 5 - D, 6 - D