Evolutionary Psychology

The goal of research in evolutionary psychology is to discover, understand, and map the human mind as well as to explore the implications of these new discoveries for other fields. The eventual aim is to map human nature—that is, the species-​typical information-​processing architecture of the human brain.

Like all cognitive scientists, when evolutionary psychologists refer to the mind, they mean the set of information-​processing devices, embodied in neural tissue, that are responsible for all conscious and nonconscious mental activity and that generate all behavior. Like other psychologists, evolutionary psychologists test hypotheses about the design of these information-​processing devices—these programs—using laboratory methods from experimental cognitive and social psychology, as well as methods drawn from experimental economics, neuropsychology, and cross-​cultural field work.

What allows evolutionary psychologists to go beyond traditional approaches in studying the mind is that they make active use in their research of an often-​overlooked fact: That the programs comprising the human mind were designed by natural selection to solve the adaptive problems faced by our hunter-​gatherer ancestors—problems like finding a mate, cooperating with others, hunting, gathering, protecting children, avoiding predators, and so on. Natural selection tends to produce programs that solve problems like these reliably, quickly, and efficiently. Knowing this information allows one to approach the study of the mind like an engineer. One starts with a good specification of an adaptive information-​processing problem and develops a task analysis of that problem. This process allows one to see what properties a program would have to have in order to solve that problem well. This approach allows one to generate testable hypotheses about the structure of the programs that comprise the mind.

Evolutionary psychology dates back to Darwin. It emerged in its present form during the 1980s and was motivated by new developments and insights from a series of different fields, among them,

• the cognitive revolution that, for the first time in human history, provided a precise language for describing mental mechanisms as programs that process information;
• advances in paleoanthropology, hunter-​gatherer studies, and primatology, which gave access to data about the adaptive problems with which our ancestors were confronted regarding how to survive and reproduce and the environments that were most conducive of this notion;
• research in animal behavior, linguistics, and neuropsychology, which showed that the mind was not a blank slate passively recording the world. (Indeed, it was discovered that organisms come factory-​equipped with knowledge about the world, which allows them to learn some relationships easily and others only with great effort, if at all, and demonstrating that Skinner’s hypothesis—that learning is a simple process governed by reward and punishment—was simply wrong); and
• evolutionary game theory, which revolutionized evolutionary biology, placing it on a more rigorous, formal foundation of replicator dynamics. This theory clarified how natural selection works, what counts as an adaptive function, and what the criteria are for calling a trait an adaptation.

A number of scientists realized that if one were careful about the causal connections between disciplines, these four new developments could be pieced together into a single integrated research framework in a way that had not been exploited before because the connections ran between fields, rather than cleanly within them. They called this framework evolutionary psychology. The framework that emerged from these advances can be summarized in six points.

First, each organ in the body evolved to serve a function: The intestines digest, the heart pumps blood, and the liver detoxifies poisons. The brain also is an organ, and its evolved function is to extract information from the environment and use that information to generate behavior and regulate physiology. From this perspective, the brain is a computer (i.e., a physical system that was designed to process information). Its programs were designed not by an engineer, but by natural selection, a causal process that retains and discards design features on the basis of how well they solve problems that affect reproduction.

The fact that the brain processes information is not an accidental side effect of some metabolic process. The brain was designed by natural selection to be a computer. Therefore, if one wants to describe its operation in a way that captures its evolved function, one needs to think of it as composed of programs that process information. The question then becomes, what programs are to be found in the human brain? What are the reliably developing, species-​typical programs that, taken together, comprise the human mind?

Second, individual behavior is generated by this evolved computer in response to information that it extracts from the internal and external environment, including the social environment. To understand an individual’s behavior, therefore, one needs to know both the information that the person registered and the structure of the programs that generated his or her behavior.

Third, the programs that comprise the human brain were sculpted over time by the ancestral environments and selection pressures experienced by the hunter-​gatherers from whom we are descended. Each evolved program exists because it produced behavior that promoted the survival of our ancestors in a way better than alternative programs that arose during human evolutionary history. Evolutionary psychologists emphasize hunter-​gatherer life because the evolutionary process is slow—it takes tens of thousands of years to build a program of any complexity. The Industrial Revolution—even the Agricultural Revolution—are mere eye blinks in evolutionary time, too short to have selected for new cognitive programs.

Fourth, although the behavior generated by our evolved programs would, on average, have been adaptive to ancestral environments, there is no guarantee that it will be so now. Modern environments differ importantly from ancestral ones—particularly when it comes to social behavior. We no longer live in small, face-​to-​face societies, in seminomadic bands of 50 to 100 people, many of whom were close relatives. Yet our cognitive programs were designed for that social world.

Fifth, and perhaps most important, the brain must be comprised of many different programs, each specialized for solving a different adaptive problem our ancestors faced (i.e., the mind cannot be a blank slate).

In fact, the same is true of any computationally powerful, multitasking computer. Consider the typical desktop computer. So many people analyze data and write prose that most computers come factory-​equipped with a spreadsheet and a text editor. These two separate programs each have different computational properties because crunching numbers and writing prose are very different problems: The design features that make a program good at data analysis are not well suited to writing and editing articles, and vice versa. To accomplish both tasks well, the computer has two programs, each well designed for a specific task. The more functionally specialized programs it has, the more intelligent the computer is and the more things it can do. The same is true for people.

Our hunter-​gatherer ancestors were, in effect, on a camping trip that lasted a lifetime, and they had to solve many different kinds of problems well to survive under those conditions. Design features that make a program good at choosing nutritious foods, for example, will be ill suited for finding a fertile mate. Different problems require different solutions. Many of these solutions—these evolved programs—will be domain-​specific: well designed for processing information about certain domains of human life (e.g., potential mates) but not others (e.g., potential foods). This idea can be most clearly seen by using results from evolutionary game theory and data about ancestral environments to define adaptive problems and then carefully dissecting the computational requirements of any program capable of solving those problems.

Last, if one wants to understand human culture and society, one needs to understand these domain-​specific programs. The mind is not like a video camera, passively recording the world, but imparting no content of its own. Domain-​specific programs organize our experiences, create our inferences, inject certain recurrent concepts and motivations into our mental life, give us our passions, educate our moral sentiments, and provide cross-​culturally universal frames of meaning that allow us to understand the actions and intentions of others. They cause us to think certain specific thoughts; they make certain ideas, feelings, and reactions seem reasonable, right, interesting, and memorable. Consequently, they play a key role in determining which ideas and customs will easily spread from mind to mind and which will not. That is, they play a crucial role in shaping human culture.

The view that humans reliably develop a large number of functionally specialized, domain-​specific programs that structure human learning, inference, and choice has stirred the most debate. Most research in the social sciences is implicitly guided by the Standard Social Sciences Model (SSSM), and a central tenet of the SSSM is that few, if any, programs of this kind exist. The SSSM assumes that the evolved architecture of the human mind is a tabula rasa equipped with a small number of content-​free programs that operate uniformly across domains. If true, then all the content of our thoughts and feelings would derive externally from the social and physical environments. None would reflect the operation of a rich human nature.

During the 20th century, many failed experiments in social engineering, especially those implemented by communist regimes, were rooted in the SSSM assumption that human desires, emotions, and motivations are infinitely plastic social constructions that can be easily molded into any form.

Instincts are often thought of as the diametric opposite of reasoning. But the reasoning programs that evolutionary psychologists have been discovering are specialized for solving adaptive problems. In addition, they reliably develop in all normal human beings without any conscious effort and in the absence of formal instruction. These programs are applied without any awareness of their underlying logic and are distinct from more general abilities to process information or behave intelligently. In other words, they have all the hallmarks of what we usually think of as an instinct. In fact, one can think of these specialized circuits as reasoning instincts. They make certain kinds of inferences just as easy, effortless, and natural to us as humans, as spinning a web is to a spider or building a dam is to a beaver.

For example, evolutionary psychologists have found that the mind reliably develops programs that are functionally specialized for reasoning about social exchange, which include a subroutine for cheater detection. This latter program is neurally isolable: After brain damage, a person can have a deficit in their ability to detect cheaters, yet have a normal IQ and be able to successfully solve reasoning problems that are logically isomorphic to those that involve cheater detection (but deal with a different adaptive domain). This evolved competence also is found cross-​culturally: It is as robustly present in nonliterate hunter-​horticulturalists in remote areas of the Amazon as it is in college-​educated individuals from market economies. When problems are constructed such that the correct answer for detecting cheaters violates rules of inference drawn from formal logics, people everywhere follow the adaptive logic of social exchange in preference to logical rules. Evolved social exchange mechanisms provide the cognitive foundations of trade.

Like many results in evolutionary psychology, research indicating that the mind has a system functionally specialized for cheater detection cuts to the heart of debates on the nature of human reasoning and rationality. It raises the possibility that the power of human intelligence comes from bundling together a collection of diverse mechanisms, each of which is specialized for reasoning about a different adaptive domain.

This position directly challenges the assumption that human rationality is accomplished by a small set of content-​free inference procedures drawn from logic, mathematics, or rational choice theory. It also challenges the “heuristics and biases” school of thought, in which human reasoning is viewed as riddled with errors and biases that prevent good judgment and decision making. For this reason, evolutionary psychology has awakened interest and debate not only in the cognitive sciences, psychology, and neuroscience, but in economics, law, anthropology, and philosophy—in every field that concerns itself with human rationality.

Many political theories and public policies rest on strong assumptions about human nature. As empirical investigations of human nature proceed, some will have to be abandoned. The assumptions about human nature, on which certain political theories are founded, will turn out to be incorrect; some policies will fail because their success requires human nature to be other than it is.

The position most central to libertarianism—that human relationships should be based on the voluntary consent of the individuals involved—makes few if any assumptions about human nature. However, these assumptions do play a role in libertarian thought. They may be found in some philosophical justifications of the libertarian position, in particular public policy recommendations, and in arguments about how institutions should be created that will preserve liberty over time. Libertarian theorists—like the Founding Fathers before them—will need to take human nature into account in deciding the best ways to implement liberty, property rights, and the rule of law.

Further Readings

Cosmides, Leda, and J. Tooby. Universal Minds: Understanding the New Science of Evolutionary Psychology. New Haven, CT: Yale University Press, 2004.

Gigerenzer, Gerd, Peter M. Todd, and the ABC Research Group. Simple Heuristics That Make Us Smart. New York: Oxford University Press, 2000.

Pinker, Steven. How the Mind Works. New York: W. W. Norton, 1997.

Tooby, J., and L. Cosmides. “Psychological Foundations of Culture.” The Adapted Mind: Evolutionary Psychology and the Generation of Culture. J. Barkow, L. Cosmides, and J. Tooby, eds. New York: Oxford University Press, 1992.

Wilkinson, Will. “Capitalism and Human Nature.” Cato Policy Report 27 no. 1 (January/​February 2005).