- Understand what evolution means.
- Define the primary mechanisms by which evolution takes place.
- Identify the two major classes of adaptations.
- Define sexual selection and its two primary processes.
- Define gene selection theory.
- Understand psychological adaptations.
- Identify the core premises of sexual strategies theory.
- Identify the core premises of error management theory, and provide two empirical examples of adaptive cognitive biases.
If you have ever been on a first date, you are probably familiar with the anxiety of trying to figure out what clothes to wear or what perfume or cologne to put on. In fact, you may even consider flossing your teeth for the first time all year. When considering why you put in all this work, you probably recognize that you are doing it to impress the other person, but how did you learn these particular behaviours? Where did you get the idea that a first date should be at a nice restaurant or someplace unique? It is possible that we have been taught these behaviours by observing others. It is also possible, however, that these behaviours — wearing fancy clothes and going to expensive restaurants — are biologically programmed into us. That is, just as peacocks display their feathers to show how attractive they are, or some lizards do push-ups to show how strong they are, when we style our hair or bring a gift to a date, we are trying to communicate to the other person: “Hey, I’m a good mate! Choose me! Choose me!”
However, we all know that our ancestors hundreds of thousands of years ago were not driving sports cars or wearing designer clothes to attract mates. So, how could someone ever say that such behaviours are “biologically programmed” into us? Well, even though our ancestors might not have been doing these specific actions, these behaviours are the result of the same driving force: the powerful influence of evolution, whereby certain traits and behaviours develop over time because they are advantageous to our survival. In the case of dating, doing something like offering a gift might represent more than a nice gesture. Just as chimpanzees will give food to mates to show they can provide for them, when you offer gifts to your dates, you are communicating that you have the money or resources to help take care of them, and even though the person receiving the gift may not realize it, the same evolutionary forces are influencing their behaviour as well. The receiver of the gift evaluates not only the gift but also the gift-giver’s clothes, physical appearance, and many other qualities to determine whether the individual is a suitable mate, but because these evolutionary processes are hardwired into us, it is easy to overlook their influence.
To broaden your understanding of evolutionary processes, the following will present some of the most important elements of evolution as they impact psychology. Evolutionary theory helps us piece together the story of how we humans have prospered. It also helps to explain why we behave as we do on a daily basis in our modern world, including why we bring gifts on dates, why we get jealous, why we crave our favorite foods, why we protect our children, and so on. Evolution may seem like a historical concept that applies only to our ancient ancestors, but, in truth, it is still very much a part of our modern daily lives.
Basics of evolutionary theory
Evolution simply means change over time. Many think of evolution as the development of traits and behaviours that allow us to survive this “dog-eat-dog” world, like strong leg muscles to run fast or fists to punch and defend ourselves. However, physical survival is only important if it eventually contributes to successful reproduction. That is, even if you live to be 100 years old, if you fail to mate and produce children, your genes will die with your body. Thus, reproductive success, not survival success, is the engine of evolution by natural selection. Every mating success by one person means the loss of a mating opportunity for another, yet every living human being is an evolutionary success story. Each of us is descended from a long and unbroken line of ancestors who triumphed over others in the struggle to survive, at least long enough to mate, and reproduce. However, in order for our genes to endure over time — to survive harsh climates or to defeat predators — we have inherited adaptive, psychological processes designed to ensure success.
At the broadest level, we can think of organisms, including humans, as having two large classes of adaptations, which are traits and behaviours that evolved over time to increase our reproductive success. The first class of adaptations are for survival and are mechanisms that helped our ancestors handle what Charles Darwin famously described as the hostile forces of nature. For example, in order to survive very hot temperatures, we developed sweat glands to cool ourselves. In order to survive very cold temperatures, we developed shivering mechanisms that contract and expand muscles to produce warmth. Other examples of survival adaptations include developing a craving for fats and sugars, encouraging us to seek out particular foods rich in fats and sugars that keep us going longer during food shortages. Some threats, such as snakes, spiders, darkness, heights, and strangers, often produce fear in us, which encourages us to avoid them in order to stay safe. These are also examples of survival adaptations. All of these adaptations are for physical survival.
The second class of adaptations are for reproduction and help us compete for mates. These adaptations are described in an evolutionary theory proposed by Darwin, called sexual selection theory. We will first spend a little time understanding sexual selection theory and, then, apply it to understanding what adaptations may have evolved in humans.
Sexual selection theory
Darwin noticed that there were many traits and behaviours of organisms that could not be explained by survival selection. For example, the brilliant plumage of peacocks should actually lower their rates of survival. That is, the feathers of a peacock act like a neon sign to predators, advertising: “Easy, delicious dinner here!” However, if these bright feathers only lower a peacock’s chances at survival, why do they have them? The same can be asked of similar characteristics of other animals, such as the large antlers of male stags or the wattles of roosters, which also seem to be unfavorable to survival. Again, if these traits only make the animals less likely to survive, why did they develop in the first place? And how have these animals continued to survive with these traits over thousands and thousands of years? Darwin’s answer to this conundrum was the theory of sexual selection: the evolution of characteristics, not because of survival advantage, but because of mating advantage.
Sexual selection occurs through two processes. The first, intrasexual competition, occurs when members of one sex compete against each other, and the winner gets to mate with a member of the opposite sex. Male stags, for example, battle with their antlers, and the winner, often the stronger one with larger antlers, gains mating access to the female. That is, even though large antlers make it harder for the stags to run through the forest and evade predators, which lowers their survival success, they provide the stags with a better chance of attracting a mate, which increases their reproductive success. Similarly, human males sometimes compete against each other in physical contests, such as boxing, wrestling, or karate. We also see this in group-on-group sports, such as football. Even though engaging in these activities poses a threat to survival success, as in the example with the stag, the victors are often more attractive to potential mates, increasing their reproductive success. Thus, whatever qualities lead to success in intrasexual competition are then passed on with greater frequency due to their association with greater mating success.
The second process of sexual selection is preferential mate choice, also called intersexual selection. In this process, if members of one sex are attracted to certain qualities in mates — such as brilliant plumage, signs of good health, or even intelligence — those desired qualities get passed on in greater numbers simply because their possessors mate more often. For example, the colourful plumage of peacocks exists due to a long evolutionary history of attraction on the part of peahens, the term for female peacocks, to males with brilliantly-coloured feathers.
In all sexually-reproducing species, adaptations in the sexes — both males and females — exist due to survival selection and sexual selection. Returning to the question of human reproductive adaptations, we might ask ourselves what these might be. For example, is there a human “equivalent” to peacock tail plumage? Are there human signals of desirable genes that are fundamentally important in human courtship? One of the challenges to understanding reproductive adaptations might be our inability to see ourselves as evolved animals subject to reproductive pressures throughout our evolutionary history just as other non-human animals have been. Furthermore, unlike other animals where one sex has dominant control over mate choice, humans have mutual mate choice. That is, both women and men typically have a say in choosing their mates, and both mates value qualities such as kindness, intelligence, and dependability that are beneficial to long-term relationships, which are qualities that make good partners and good parents. Understanding human adaptations requires us to think critically about the life challenges that have impacted humans over millennia. Unfortunately, our knowledge of these challenges is limited and sometimes requires us to make assumptions rather than rely on hard evidence.
Gene selection theory
In modern evolutionary theory, all evolutionary processes boil down to an organism’s genes. Genes are the basic units of heredity; that is, genes are the information that is passed along in DNA that tells the cells and molecules how to “build” the organism and how that organism should behave. Genes that are better able to encourage the organism to reproduce, thus replicating themselves in the organism’s offspring, have an advantage over competing genes that are less able. For example, take female sloths. In order to attract a mate, they will scream as loudly as they can to let potential mates know where they are in the thick jungle. Now, consider two types of genes in female sloths: one gene that allows them to scream extremely loudly and another that only allows them to scream moderately loudly. In this case, the female sloth with the gene that allows her to shout louder will attract more mates — increasing reproductive success — which ensures that her genes are more readily passed on than those of the quieter sloth.
Essentially, genes can boost their own replicative success in two basic ways. First, they can influence the odds for survival and reproduction of the organism they are in; this is called individual reproductive success or fitness, as we saw in the example with the sloths. Second, genes can also influence the organism to help other organisms who also likely contain those genes — known as “genetic relatives” — to survive and reproduce; this is called inclusive fitness. For example, why do human parents tend to help their own kids with the financial burdens of a college education and not the kids next door? Well, having a college education increases one’s attractiveness to other mates, which in turn increases one’s likelihood for reproducing and passing on genes. Because parents’ genes are in their own children, and not the neighbourhood children, funding their children’s educations increases the likelihood that the parents’ genes will be passed on.
Understanding gene replication is the key to understanding modern evolutionary theory. It also fits well with many evolutionary psychological theories. However, for the time being, we will move beyond our discussion of genes and focus primarily on actual adaptations that evolved because they helped our ancestors survive and/or reproduce.
Evolutionary psychology aims the lens of modern evolutionary theory on the workings of the human mind. It focuses primarily on psychological adaptations, which are mechanisms of the mind that have evolved to solve specific problems of survival or reproduction. These kinds of adaptations are in contrast to physiological adaptations, which are adaptations that occur in the body as a consequence of one’s environment. One example of a physiological adaptation is how our skin makes calluses. First, there is an “input,” such as repeated friction to the skin on the bottom of our feet from walking. Second, there is a “procedure,” in which the skin grows new skin cells at the afflicted area. Third, a callus forms as an “output” to protect the underlying tissue; the tougher skin to protect repeatedly scraped areas is the final outcome of the physiological adaptation. On the other hand, a psychological adaptation is a development or change of a mechanism in the mind. For example, take sexual jealousy. First, there is an “input,” such as a romantic partner flirting with a rival. Second, there is a “procedure,” in which the person evaluates the threat the rival poses to the romantic relationship. Third, there is a behavioural “output,” which might range from vigilance (e.g., snooping through a partner’s email) to violence (e.g., threatening the rival).
Evolutionary psychology is fundamentally an interactionist framework, taking into account multiple factors when determining an outcome. For example, jealousy, like a callus, does not simply pop up out of nowhere. There is an interaction between the environmental trigger (e.g., the flirting or the repeated friction to the skin) and the initial response (e.g., evaluation of the flirter’s threat or the forming of new skin cells) to produce the outcome.
In evolutionary psychology, culture also has a major effect on psychological adaptations. For example, status within one’s group is important in all cultures for achieving reproductive success because higher status makes someone more attractive to mates. In individualistic cultures, such as Canada, status is heavily determined by individual accomplishments; however, in more collectivist cultures, such as Japan, status is more heavily determined by contributions to the group and by that group’s success. For example, consider a group project. If you were to put in most of the effort on a successful group project, the culture in Canada reinforces the psychological adaptation to try to claim that success for yourself since individual achievements are rewarded with higher status. However, the culture in Japan reinforces the psychological adaptation to attribute that success to the whole group since collective achievements are rewarded with higher status. Another example of cultural input is the importance of virginity as a desirable quality for a mate. Cultural norms that advise against premarital sex persuade people to ignore their own basic interests because they know that virginity will make them more attractive marriage partners. Evolutionary psychology, in short, does not predict rigid, robotic-like “instincts.” That is, there is not one rule that works all the time. Rather, evolutionary psychology studies flexible, environmentally-connected, and culturally-influenced adaptations that vary according to the situation.
Psychological adaptations are hypothesized to be wide-ranging, and they include food preferences, habitat preferences, mate preferences, and specialized fears. These psychological adaptations also include many traits that improve people’s ability to live in groups, such as the desire to cooperate and make friends or the inclination to spot and avoid frauds, punish rivals, establish status hierarchies, nurture children, and help genetic relatives. Research programs in evolutionary psychology develop and empirically test predictions about the nature of psychological adaptations. Below, we highlight a few evolutionary psychological theories and their associated research approaches.
Sexual strategies theory
Sexual strategies theory is based on sexual selection theory. It proposes that humans have evolved a list of different mating strategies, both short-term and long-term, that vary depending on culture, social context, parental influence, and personal mate value, which is one’s desirability in the mating market.
In its initial formulation, sexual strategies theory focused on the differences between men and women in mating preferences and strategies (Buss & Schmitt, 1993). It started by looking at the minimum parental investment needed to produce a child. For women, even the minimum investment is significant. After becoming pregnant, women have to carry the child for nine months inside of them. For men, on the other hand, the minimum investment to produce the same child is considerably smaller — simply the act of sex.
These differences in parental investment have an enormous impact on sexual strategies. For a woman, the risks associated with making a poor mating choice is high. She might get pregnant by a man who will not help to support her and her children or who might have poor-quality genes. Since the stakes are higher for a woman, wise mating decisions for her are much more valuable. For men, on the other hand, the need to focus on making wise mating decisions is not as important. That is, unlike women, men do not biologically have the child growing inside of them for nine months, and they do not have as high a cultural expectation to raise the child. This logic leads to a powerful set of predictions. In short-term mating, women will likely be choosier than men because the costs of getting pregnant are so high, while men, on average, will likely engage in more casual sexual activities because this cost is greatly lessened. Due to this, men will sometimes deceive women about their long-term intentions for the benefit of short-term sex, and men are more likely than women to lower their mating standards for short-term mating situations.
An extensive body of empirical evidence supports these and related predictions (Buss & Schmitt, 2011). Men express a desire for a larger number of sex partners than women do. They let less time elapse before seeking sex. They are more willing to consent to sex with strangers and are less likely to require emotional involvement with their sex partners. They have more frequent sexual fantasies and fantasize about a larger variety of sex partners. They are more likely to regret missed sexual opportunities; as such, they may lower their standards in short-term mating, showing a willingness to mate with a larger variety of women as long as the costs and risks are low.
However, in situations where both the man and woman are interested in long-term mating, both sexes tend to invest substantially in the relationship and in their children. In these cases, the theory predicts that both sexes will be extremely choosy when pursuing a long-term mating strategy. Much empirical research supports this prediction as well. In fact, the qualities women and men generally look for when choosing long-term mates are very similar: both want mates who are intelligent, kind, understanding, healthy, dependable, honest, loyal, loving, and adaptable.
Nonetheless, women and men do differ in their preferences for a few key qualities in long-term mating because of somewhat distinct adaptive issues. Modern women have inherited the evolutionary trait to desire mates who possess resources, have qualities linked with acquiring resources (e.g., ambition, wealth, or industriousness), and are willing to share those resources with them. On the other hand, men more strongly desire youth and health in women, as both are cues to fertility. These male and female differences are universal in humans. They were first documented in 37 different cultures, from Australia to Zambia (Buss, 1989), and have since been replicated by dozens of researchers in dozens of additional cultures (Buss, 2012).
As we know, though, just because we have these mating preferences — that is, men with resources or fertile women being preferred — people do not always get what they want. There are countless other factors which influence who people ultimately select as their mate. For example, the sex ratio (i.e., the percentage of men to women in the mating pool), cultural practices (e.g., arranged marriages, which inhibit an individual’s freedom to act on their preferred mating strategies), the strategies of others (e.g., if everyone else is pursuing short-term sex, it’s more difficult to pursue a long-term mating strategy), and many others all influence who we select as our mates. Furthermore, the availability of contraception allows a degree of conscious control over reproduction that is unprecedented in human history; the evolved sex differences in approaches to courtship and mating may be expressed differentially according to the use of contraception.
Sexual strategies theory, which is anchored in sexual selection theory, predicts specific similarities and differences in men and women’s mating preferences and strategies. Whether we seek short-term or long-term relationships, many personality, social, cultural, and ecological factors will all influence who our partners will be.
Error management theory
Error management theory (EMT) deals with the evolution of how we think, make decisions, and evaluate uncertain situations — that is, situations where there is no clear answer about how we should behave (Haselton & Buss, 2000; Haselton, Nettle, & Andrews, 2005). Consider, for example, walking through the woods at dusk. You hear a rustle in the leaves on the path in front of you. It could be a snake, or it could just be the wind blowing the leaves. Because you can’t really tell why the leaves rustled, it’s an uncertain situation. The important question, then, is to ask what the costs of errors in judgment are. In this case, if you conclude that it is a dangerous snake, you avoid the leaves, making a short detour around them, and the costs are minimal. However, if you assume the leaves are safe and simply walk over them — when in fact it is a dangerous snake — the decision could cost you your life.
Now, think about our evolutionary history and how generation after generation was confronted with similar decisions, where one option had low cost but great reward (e.g., walking around the leaves and not getting bitten) and the other had a low reward but high cost (e.g., walking through the leaves and getting bitten). These kinds of choices are called cost asymmetries. If during our evolutionary history we encountered decisions like these generation after generation, over time an adaptive bias would be created. We would make sure to err in favor of the least costly — in this case, least dangerous — option (e.g., walking around the leaves). To put it another way, EMT predicts that whenever uncertain situations present us with a safer versus more dangerous decision, we will psychologically adapt to prefer choices that minimize the cost of errors.
EMT is a general evolutionary psychological theory that can be applied to many different domains of our lives, but a specific example of it is the visual descent illusion. Have you ever thought it would be no problem to jump off of a ledge, but as soon as you stood up there, it suddenly looked much higher than you thought? The visual descent illusion (Jackson & Cormack, 2008) states that people will overestimate the distance when looking down from a height, compared to looking up, so that people will be especially wary of falling from great heights, which would result in injury or death. Another example of EMT is the auditory looming bias. Have you ever noticed how an ambulance seems closer when it’s coming toward you, but suddenly seems far away once it’s immediately passed? With the auditory looming bias, people overestimate how close objects are when the sound is moving toward them compared to when it is moving away from them. From our evolutionary history, humans learned that it is better to be safe than sorry. Therefore, if we think that a threat is closer to us when it is moving toward us because it seems louder, we will be quicker to act and escape. In this regard, there may be times we ran away when we did not need to, reacting to a false alarm, but wasting that time is a less costly mistake than not acting in the first place when a real threat does exist.
EMT has also been used to predict adaptive biases in the domain of mating. Consider something as simple as a smile. In one case, a smile from a potential mate could be a sign of sexual or romantic interest. On the other hand, it may just signal friendliness. In light of the costs to men of missing out on chances for reproduction, EMT predicts that men have a sexual overperception bias; they often misread sexual interest from a woman when really it’s just a friendly smile or touch. In the mating domain, the sexual overperception bias is one of the best-documented phenomena. It has been shown in studies in which men and women rated the sexual interest between people in photographs and videotaped interactions. As well, it has been shown in the laboratory with participants engaging in speed dating where the men interpret sexual interest from the women more often than the women actually intended it (Perilloux, Easton, & Buss, 2012). In short, EMT predicts that men, more than women, will over-infer sexual interest based on minimal cues, and empirical research confirms this adaptive mating bias.
Sexual strategies theory and error management theory are two evolutionary psychological theories that have received much empirical support from dozens of independent researchers. However, there are many other evolutionary psychological theories, such as social exchange theory, that also make predictions about our modern-day behaviour and preferences. The merits of each evolutionary psychological theory, however, must be evaluated separately and treated like any scientific theory. That is, we should only trust their predictions and claims to the extent they are supported by scientific studies. Even if the theory is scientifically grounded, just because a psychological adaptation was advantageous in our history, it does not mean it is still useful today. For example, even though women may have preferred men with resources generations ago, our modern society has advanced such that these preferences are no longer apt or necessary. Nonetheless, it is important to consider how our evolutionary history has shaped our automatic or instinctual desires and reflexes of today so that we can better shape them for the future ahead.
Source: Adapted from Buss (2020).
- Adaptations are evolved solutions to problems that historically contributed to reproductive success.
- Error management theory is a theory of selection under conditions of uncertainty in which recurrent cost asymmetries of judgment or inference favor the evolution of adaptive cognitive biases that function to minimize the more costly errors.
- Evolution is change over time, but is the definition changing?
- Gene selection theory is the modern theory of evolution by selection by which differential gene replication is the defining process of evolutionary change.
- Intersexual selection is a process of sexual selection by which evolution — that is, change — occurs as a consequences of the mate preferences of one sex exerting selection pressure on members of the opposite sex.
- Intrasexual competition is a process of sexual selection by which members of one sex compete with each other, and the victors gain preferential mating access to members of the opposite sex.
- Natural selection is differential reproductive success as a consequence of differences in heritable attributes.
- Psychological adaptations are mechanisms of the mind that evolved to solve specific problems of survival or reproduction, conceptualized as information processing devices.
- Sexual selection is the evolution of characteristics because of the mating advantage they give organisms.
- Sexual strategies theory is a comprehensive evolutionary theory of human mating that defines the menu of mating strategies humans pursue, the adaptive problems women and men face when pursuing these strategies, and the evolved solutions to these mating problems.
- How does change take place over time in the living world?
- Which two potential psychological adaptations to problems of survival are not discussed in this section?
- What are the psychological and behavioural implications of the fact that women bear heavier costs to produce a child than men do?
- Can you formulate a hypothesis about an error management bias in the domain of social interaction?
Buss, D. M. (1989). Sex differences in human mate preferences: Evolutionary hypotheses tested in 37 cultures. Behavioral & Brain Sciences, 12, 1–49.
Buss, D. M. (2012). Evolutionary psychology: The new science of the mind (4th ed.). Boston, MA: Allyn & Bacon.
Buss, D. M. (2020). Evolutionary theories in psychology. In R. Biswas-Diener & E. Diener (Eds.), Noba textbook series: Psychology. Champaign, IL: DEF publishers. Retrieved from http://noba.to/ymcbwrx4
Buss, D. M., & Schmitt, D. P. (1993). Sexual strategies theory: An evolutionary perspective on human mating. Psychological Review, 100, 204–232.
Buss, D. M., & Schmitt, D. P. (2011). Evolutionary psychology and feminism. Sex Roles, 64, 768–787.
Haselton, M. G., & Buss, D. M. (2000). Error management theory: A new perspective on biases in cross-sex mind reading. Journal of Personality and Social Psychology, 78, 81–91.
Haselton, M. G., Nettle, D., & Andrews, P. W. (2005). The evolution of cognitive bias. In D. M. Buss (Ed.), The handbook of evolutionary psychology (pp. 724–746). New York, NY: Wiley.
Jackson, R. E., & Cormack, J. K. (2008). Evolved navigation theory and the environmental vertical illusion. Evolution and Human Behavior, 29, 299–304.
Perilloux, C., Easton, J. A., & Buss, D. M. (2012). The misperception of sexual interest. Psychological Science, 23, 146–151.