- Discuss the claim that nothing in psychology makes sense except in the light of evolution.
- Explain the process of natural selection and provide an example.
- Describe what is meant by adaptation and explain what is meant by a psychological adaptation.
- Explain how evolution can be nonrandom, yet still without purpose.
- Describe what William James meant by the term "instincts" applied to humans, according to Cosmides and Tooby.
- Discuss how evolutionary psychologists conceptualize human nature.
- Discuss evolution as the unifying principle for psychology, given that evolution is the unifying principle for all of biology.
- Discuss how two types of selection (hint: one of these is kin selection) may explain the duality of human moral nature and feelings of moral conflict.
- Describe the primary features of evolutionary psychology as an approach to the study of the mind and brain.
Why do humans and other animals move, why do they have particular mental capabilities and not others, and what laws or principles govern the organization of behavior and mental processes? In this section, the concept of evolution will be introduced and the insights it can provide regarding mind and behavior considered. When we recognize that mental activities and behavior in humans and other animals are the product of a biological organ, the brain, we can then apply principles of biological science to an understanding of psychology. This approach focuses attention on the biological functions served by mental abilities and behavior and how they contribute to adaptation to environmental change.
Evolution, Natural Selection, and Psychological Adaptation
“In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation.” Charles Darwin, On the Origin of Species (1859/1996, p. 394)
“Nothing in biology makes sense except in the light of evolution.” Theodosius Dobzhansky (1973, p. 125)
When looking at nature, it is important to ask why things in nature have the properties that they do. This is especially important when thinking about organisms. Why do organisms possess the traits that they do? Why do birds have feathers? Why do we have emotions and why are our emotions so similar to the emotions found in a wide range of other animal species? Why do we have the capacity to think, why does our thinking take the forms that it does, and why are many of our thinking processes fundamentally similar to the thinking processes found in many other animal species? Why do we see color, while many other species don't? Why do we have the capacity to form mental images of the past and of imagined futures?
Psychology is the scientific study of mental processes and behavior. These processes are, of course, all functions of a biological organ, the brain. Like other organs, the brain and its operations have evolutionary origins. Understanding evolution can give us fresh insights about our psychology and the psychology of other species. The characteristics of organisms, including mental and behavioral traits, perform biological functions that contribute to survival and reproduction.
The minds and behavior of organisms have been shaped by evolutionary forces over millions of years, just like their anatomical and physiological features. To the trained eye, the mark of evolution is still evident in the psychology of present-day humans and other animals. And, as Darwin's principle of the continuity of species predicts, human and animal species, although diverse, show fundamental similarities in mind and behavior just as they do in their anatomy and physiology. Although there are many factors that affect evolution, the key driving force in evolution is the process of natural selection (Dawkins, 1976, 1982).
Darwin was not the first to propose that species evolve, that they change over time. Darwin's brilliant insight was the discovery of the primary process which guides evolutionary change--natural selection, the survival and reproduction of the "fittest". "Fit" in this context does not mean the healthiest or the strongest, rather it is a reference to the ability to pass one's genes on to the next generation. Natural selection is similar to artificial selection, a process used by animal breeders to enhance characteristics which they deem desirable. But in natural selection it is the environment that does the selection.
Natural selection acts on natural variation within populations. One important feature of life is that individual organisms within any sexually-reproducing species vary from one another in countless ways. Natural selection works because some individuals are better suited to the environment than others; those individuals better fit to the environment have a competitive advantage and naturally survive and reproduce in greater numbers and therefore pass on their heritable (genetic) traits to succeeding generations with greater frequency. This is the essence of evolution.
Evolution by natural selection is inevitable given three factors:
- genetic variation in heritable traits in a population of reproducing organisms due to mutation and the mixing of genes during sexual reproduction;
- competition among members of the population for limited environmental resources;
- those individuals who are better suited, better "fit," to the demands and opportunities of the environment have a competitive advantage and therefore survive and reproduce in greater numbers. The result is the proliferation of the genes and traits which provide superior fitness to the environment. Fitness is measured not simply in terms of survival, but more importantly by reproductive success, the number of living offspring that are produced.
In other words, some individuals, by chance, happen to have genetic characteristics that make them better prepared to survive and reproduce, leading their genes to be selected and to persist in future generations. By this process of selection, traits which give a competitive edge in solving problems of survival and reproduction and in exploiting environmental opportunities tend to be preserved over generations, while traits less well-suited are removed. For example, those better at predator avoidance, better at obtaining energy from food, better at successful mating, or better at inventing ways to use the environment for adaptive advantage survive and reproduce more offspring. By this process of natural selection, over countless generations, species of living things evolve characteristics (including mental and behavioral traits) that are well-adapted to solve problems and to exploit opportunities in their particular environments. Gradually, over long periods of time, organisms acquire adaptive "design" by completely natural and unintentional processes. Note that as the environment changes, new traits may evolve. In a sense, evolutionary change tracks changes in the environment, creating an improving match between organism and environment over evolutionary time.
Nevertheless, relatively rapid changes in the environment may outpace the rate of evolutionary change. This means that adaptations that evolved for an earlier environment may not necessarily be well suited to the current environment. This is important in understanding some of the psychological traits of humans that were once advantageous, but which have now become non-adaptive. For example, some experts have argued that humans have an innate disposition to be territorial and to be suspicious and wary of strangers, of outsiders, and perhaps even hostile to those outside of their own group. Although this may have been an adaptive psychological trait in our ancient Pleistocene past when humans lived in small groups of hunter-gatherers, in today's world these tendencies may dispose us toward prejudice and even dangerous and wasteful wars.
Environmental Selection and Sexual Selection
The type of natural selection discussed above is environmental selection--selection by the environment of which genetic variants in a population will survive long enough to have a chance to reproduce. Note that the environment "selects" who will survive and who won't by virtue of the fact that the environment presents challenges to survival such as disease, predators, and insufficient supplies of resources such as energy (in the form of sunlight for plants, or food for animals), territory, and water. The "selection" by the environment occurs when individuals that just happen to be better suited to meet the challenges presented by the environment naturally have a competitive advantage and survive and reproduce in greater numbers than those unlucky individuals who are less well fit to the environment.
In addition to environmental selection, in sexually reproducing species, there is a second layer of selection, sexual selection--selection based on the "attractiveness" of potential sexual partners. All other factors being equal, individuals with genes that make them more attractive to the opposite sex tend to have more reproductive opportunities and, at least in times past, tend to have more offspring than those perceived to be less attractive. This effect is in part due to the fact that bodily features associated with health and likely reproductive success tend to be perceived as sexually attractive (presumably as a result of brain evolution).
Evolution is neither random nor purposeful
It is important to note, as described above, that although evolution depends on random variations (in traits and genes) among individuals within a population, evolution is not a random process--natural selection acts on the random variation, constraining it toward successful adaptation. As Buss and Hawley (2010, p. ix) state, “Individual differences are indispensable for natural selection. Without heritable variants, natural selection—the only known process capable of creating and maintaining functional adaptations—could not occur.” In this way, evolution is not random as some who don't understand the process are apt to claim--natural selection gives it direction.
Furthermore, it is important to note that evolution is not purposeful, even though it is not random. Evolution happens automatically, without purpose, simply as a result of differential rates of reproduction in a population occurring as a consequence of the fact that individuals in a population with traits (and genes) that are more successful in a particular environment end up surviving and producing more offspring than their competitors--that's natural selection. This results in changes in gene frequencies in populations of organisms, and that is evolution. As biologist, Theodosius Dobzhansky (1964, p.449), stated: "My genes are different sequences of the same four "letters" of the "genetic alphabet" which also compose the genes of a fish or of a corn plant. Genes reproduce themselves generally with an astonishing accuracy; the sequences of the four 'letters,' the nucleotide bases, are usually identical in hundreds of billions of cells of the bodies of the parents and of their progeny. Occasionally, there occur, however, changes, "misprints," mutations. Self-reproduction plus mutation make possible natural selection. Natural selection makes possible evolution." We might even say that given these conditions, natural selection and evolution are not only possible, but inevitable.
The heritable features which organisms use to solve problems of survival and reproduction are called adaptations. These evolved adaptations can be anatomical, such as having wings or fur; physiological, such as digestive processes or having an immune system; and behavioral and mental (i.e. psychological). The evolved behavioral and mental traits of an organism are its psychological adaptations (e.g. having a fear response to danger; feelings of sexual attraction which draw you toward desirable potential mates; having a "sweet tooth" that drives you to seek out and ingest high caloric foods; having tender feelings toward your offspring motivating care-giving; understanding cause-effect relations and making causal inferences; having the mental ability to imagine future actions and to mentally anticipate the probable outcomes of those actions; and so on). According to psychologists who favor an evolutionary perspective, the mind can be seen as a large collection of evolved psychological adaptations (not all psychologists agree with this view; see Panksepp and Panksepp, 2000). These psychological adaptations are built by evolution into the structure of the brain and its physical operations. These psychological adaptations can be quite specific and concrete, such as the innate emotions related to pair-bonding and mating (e.g. "falling in love") or inborn human taste preferences for sweets and fats (see Cosmides and Tooby, 1997), or they can be quite general and abstract instincts of thought such as the innate disposition to understand the world in terms of cause-effect, to be sensitive to predictability between events, and to form categories and inferences based on similarities among things. These and other instincts of thought make up much of what we call intelligence (Koenigshofer, 2017).
In humans, psychological adaptations such as the emotions involved in mate selection, pair bonding, and mating are often associated with learned ritual behaviors that are culturally transmitted over generations and become part of the culture of particular human groups (see Figure 3.1.2). Such cultural practices are often based on commonly held "myths" that unify and help identify large groups of humans as culturally distinct from one another while facilitating cooperative effort among the members of such large groups toward common goals. According to one author (Harari, 2014), this ability to form cultural myths that imbue large numbers of strangers with a common identity, permitting them to work toward common goals, is unique to humans and accounts, in large part, for the unprecedented success of our species compared to all others. However, it is important to realize that this ability to form unifying myths depends upon features of the human brain that don't exist in sufficient degree in other animal species. Myths associated with cultural practices ranging from marriage or child birth to religious ritual or imperialism require the ability to form abstract concepts. Although research shows that non-human animal species can form concepts (Smith et al., 2010; Zentall et al., 2008), human concepts are highly abstract, apparently uniquely so, and ability for high levels of abstraction may depend upon the unique complexity of the human cerebral cortex (Koenigshofer, 2017; see Chapter 14 on Intelligence and Cognition). However, in addition, to ability to form abstract concepts, ability to learn and to transmit learned knowledge and behaviors from one generation to the next (cultural transmission) was essential to human uniqueness, and this ability to transmit learned information from generation to generation, by tradition and other non-genetic means, also depended upon particular features of the human brain (see Chapters 14 and 15 and sections 18.5 and 18.13). Thus, the great accomplishments of human civilization, which set us so clearly apart from other species, ultimately depended upon human brain evolution setting the stage, with human cultural evolution superimposed and critically dependent on brain evolution. One specific example may help drive the point home. Many experts believe that human tool making and tool use were extremely important in human evolution and early human adaptive success (see sections 3.3 and 18.5). The manufacture of stone tools by early humans was a complex and sophisticated cognitive and manual task beyond the capability of all other primates. Orban and colleagues (2006) identified a set of regions in the dorsal intraparietal sulcus (IPS) of the human cerebral cortex which they believe perform the complex visual analysis needed for the precision with which humans manipulate tools; these brain areas are not found in monkeys. Thus, a key product of human cultures was only possible because of unique features evolved in the human brain. This is only one example of a general claim: human cultural achievements that make our species so unique depend upon unique features of human brain evolution.
Individual Selection, Kin Selection, and Human Moral Conflict
From an evolutionary perspective, the minds and behavior of humans and animals, just like their anatomy and physiology, have evolved in service of survival and reproduction, either through the reproduction of one's own genes, or indirectly through the survival and reproduction of close relatives and their genes (Dawkins, 1976). The former (individual selection) favors the self-interested side of human nature; the latter (kin selection) favors our altruistic side including prosocial behaviors such as caring, giving, sharing, and cooperation (some of the adaptive benefits of living in groups in social species such as humans, wolves, lions, chimpanzees, elephants, etc). In humans at least, self-interest and the interests of others often conflict, generating psychological tension experienced as moral dilemma. For humans, it is likely that there is an optimal balance between these two opposing behavioral dispositions; an extreme, maladaptive imbalance can lead to psychopathologies such as narcissistic and anti-social personality disorders. The duality of human moral nature may have roots in the duality of these two evolutionary processes, selection for survival and reproduction of one's own genes and kin selection, selection for survival and reproduction of the genes of close genetic relatives (Koenigshofer, 2010, 2016).
Because psychological adaptations are located in the brain and its operations, these adaptations can be understood as information processing features of neural systems. On this view, the brain is a computational machine comprised of an enormous number of computational systems or modules, essentially mini-computers, made of circuits of neurons whose circuit configurations and operations have been shaped by evolutionary forces, developmental processes, and environmental experiences.
As noted in the opening quote above, Darwin recognized the relevance of evolution to psychology. Others have followed his lead. As Cosmides and Tooby (1997, p. 1) state, "In the final pages of the Origin of Species, after he had presented the theory of evolution by natural selection, Darwin made a bold prediction: 'In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation.' Thirty years later, William James tried to do just that in his seminal book, Principles of Psychology, one of the founding works of experimental psychology (James, 1890). In Principles, James talked a lot of "instincts". This term was used to refer (roughly) to specialized neural circuits that are common to every member of a species and are the product of that species' evolutionary history. Taken together, such circuits constitute (in our own species) what one can think of as 'human nature.'"
Today, the influence of these early thinkers is expressed in evolutionary approaches to psychology. Cosmides and Tooby (1997, p. 1) state: "The goal of research in evolutionary psychology is to discover and understand the design of the human mind. Evolutionary psychology is an approach to psychology, in which knowledge and principles from evolutionary biology are put to use in research on the structure of the human mind. It is not an area of study, like vision, reasoning, or social behavior. It is a way of thinking about psychology that can be applied to any topic within it. In this view, the mind is a set of information-processing machines that were designed by natural selection to solve adaptive problems faced by our hunter-gatherer ancestors." Furthermore, they explain, "Psychology is that branch of biology that studies (1) brains, (2) how brains process information, and (3) how the brain's information-processing programs generate behavior. Once one realizes that psychology is a branch of biology, inferential tools developed in biology -- its theories, principles, and observations -- can be used to understand psychology" (Cosmides and Tooby, 1997 p. 3).
Evolutionary psychologists have applied this approach to emotion (Johnston, 1999; Ketelaar, 2015), intelligence and cognition (Bouchard, 2014; Koenigshofer, 2017; Pika, et al., 2020), personality (Buss and Hawley, 2010; Figueredo, et al., 2009), language (Corballis, 2010; Fitch, 2010; Pinker, 2003), social cognition (Fiddick, 2015; Vonk, et al., 2015), and a wide range of other psychological processes. Evolution by natural selection is gaining increasing acceptance among psychologists as "a strong candidate for central inclusion in a unifying meta-theory of psychology" (Marsh and Boag, 2013, p. 655; also see Goetz & Shackelford, 2006), just as evolution has become the unifying principle for all of biology. As you read about evolution and its mechanisms in the following sections, keep in mind that not only physical traits evolve, but mental and behavioral traits and capabilities (psychological traits) do as well.
In the remainder of this chapter we examine the processes of evolution in greater detail including primate and human evolution, and evolutionary theories in psychology. To emphasize the importance of evolution to an understanding of mind and behavior, recall the claim stated above: Nothing in psychology "makes sense except in the light of evolution."
Behavior and the information processing mechanisms that underlie behavior are biological processes (in their origin and functions), dependent upon a biological organ, the brain. Just as evolution by natural selection is the organizing principle for all of biology, it must be a key organizing principle for psychology as well. Natural selection is the primary driving force of evolution, although other processes (examined in other sections of this chapter) are also involved. Natural selection occurs automatically without purpose or goal simply as a mechanistic consequence of two facts of life: 1) that individuals of any species vary from one another in their heritable traits, and 2) that some individuals by chance, because of the traits they possess (and the genes that underlie those traits), have a competitive advantage that favors their rates of survival and reproduction in a particular environment compared to those variants that are less fit. Therefore, the individuals (and the underlying genes) that are best fit to the environment end up leaving more surviving offspring and therefore have a disproportionately greater impact on the genes and traits of future generations. As a consequence, evolution occurs over generations, causing species to accumulate traits that are a better fit to survival and reproduction in the particular environments they occupy. For biological psychology, it is important to recognize that in addition to anatomy and physiology, psychological traits are also shaped into adaptive form by these same processes. Thus, to understand human and animal behavior, an evolutionary approach provides a biological context within which we can examine origins, functions, and organizing principles of minds and behavior. This approach does not negate or deny the influence of learning and culture but views these processes as biological phenomenon with evolutionary and neurophysiological roots in the brain.
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