Evolution and Human Behavior: How We Are the Same

Group Living, Language, and Theory of Mind

Group living contributed to survival in ages past. Groups were required to care for highly vulnerable offspring, to provide protection from predators, and to enable greater success in hunting game and finding foraging areas. The ability to produce and understand language facilitates living in groups because it allows people to convey not only emotions and intentions but also beliefs, attitudes, and complex thoughts to others.

There is strong evidence that infants are born with their brains “prewired” to acquire language, perhaps because of its importance to humans living in groups (Pinker, 1994). Children typically learn language at developmental stages that are almost identical across different cultures. At birth, all infants can produce the full range of possible sounds (phonemes) that exist in the totality of languages spoken anywhere on Earth, and they babble all these sounds in the crib. Language acquisition consists of dropping all the “wrong” phonemes—the ones that are not used by the particular language or languages the child hears as an infant. Thus, children can learn to speak any language depending on where they grow up. They can learn to speak a language perfectly well even if they grow up with deaf parents who never speak at all. Twins can sometimes develop their own unique language in the crib, a language that follows rules of grammar in the same way that formally recognized languages do (Pinker, 1994, 2002). These findings indicate that there are general, inherited propensities to develop grammatical language.

Just as evolution has prepared humans to live together in groups and to communicate in order to promote survival and reproduction, it may also have provided humans with a “theory of mind”—the ability to recognize that other people have beliefs and desires and that understanding others’ beliefs and desires allows us to understand and predict their behavior. Children recognize this before the age of 2 (Asch, 1952; Kuhlmeier, Wynn, & Bloom, 2003; Leslie, 2000; Malle, Moses, & Baldwin, 2001). By the age of 3 or 4, theory of mind is sophisticated enough that children can recognize when other people’s beliefs are false (Wellman, 1990).

Some of the most powerful evidence for a biologically based theory of mind comes from studying people who, due to a genetic variation, appear to have extreme difficulty in developing a theory of mind. Such a claim has been made about people with autism, a condition characterized by difficulties in interacting and communicating with others—particularly in relation to mental states like feelings and thoughts. Autistic individuals have difficulty comprehending others’ desires or beliefs and understanding that others’ beliefs might be false (Perner et al., 1989; Tager-Flusberg, 2007). It seems plausible that evolution has provided us with a kind of understanding that is too universally essential to depend on laborious trial-and-error learning. Given the importance of accurately understanding other people’s beliefs and intentions, it would not be surprising that a theory of mind comes prewired.

Avoiding the Naturalistic Fallacy

Evolutionary theory as applied to human behavior is controversial. For example, some people particularly object to the claim that there are biologically based differences between women and men in behaviors related to mate choice. Such notions are controversial in part because they follow a long history of mistaken claims about biological differences that have been used to legitimize and perpetuate male privilege (S. L. Bem, 1993).

Evolutionary claims can also lead people to assume, mistakenly, that biology is destiny—that what we are biologically predisposed to do is what we inevitably will do and perhaps even should do. This claim—that the way things are is the way they should be—is known as the naturalistic fallacy. It has no logical foundation. We are predisposed to do many things that we can overcome. Virtually all human societies are plagued by violence, for example, but the incidence of it over the past few centuries has declined dramatically. The chances of being murdered in various parts of England, for instance, declined from the thirteenth century to the twentieth by factors ranging from 10 to 100 (Pinker, 2011). The percentage of the population killed in wars has declined more or less steadily over the past few thousand years. Civilization can be regarded as the unceasing attempt to modify much of what comes naturally, reducing the extent to which human life, as seventeenth-century philosopher Thomas Hobbes put it, is “poor, nasty, brutish, and short.”

Just because a theory can be misused is no reason to reject the theory in all its aspects. While there is no justification for rejecting evolutionary ideas out of hand, caution about evolutionary claims is essential.

Social Neuroscience

Evolutionary approaches to social behavior alert us to the fact that everything humans do or think involves biological processes in the brain and body that have been shaped by natural selection. In recent years, social psychologists have begun to examine the biological grounding for behavior: the brain. This new field is called social neuroscience.

The brain may be the most complex living system in the universe, with 100 billion neurons organized into at least 50 distinct regions, and with each neuron connecting on average to 15,000 other neurons. One of the chief tools that social psychologists use to understand the brain’s role in social behavior is a technology known as functional magnetic resonance imaging (fMRI). When a person is talking with another person, making a moral judgment, or experiencing fear or outrage, blood flows to the areas of the brain that are activated. Scientists can take a picture of the brain that detects this blood flow, thus showing which brain regions are involved in the social behavior of interest.

As social neuroscience has matured, it has revealed just how social the human brain is (Lieberman, 2013). Older regions of the brain that we share with other mammals appear to be involved in nonconscious, automatic reactions to our social environment. For example, the amygdala, an almond-shaped region of the brain colored yellow in Figure 1.5, is involved in gut feelings, especially those of a fearful nature, about salient stimuli we encounter in the environment—strangers, threatening images, people from adversarial groups (W. A. Cunningham & Brosch, 2012; Ochsner & Lieberman, 2001). Near the amygdala is another old, mammalian region of the brain known as the nucleus accumbens, colored red in Figure 1.5. This area is rich with receptors for dopamine, the chemical associated with reward. The area projects to the prefrontal cortex at the front of the brain, where we process complex thoughts and emotions. The nucleus accumbens is thought of as the brain’s “reward circuit.” It signals to the individual in quick, automatic fashion what is rewarding in the environment, be it the smile of a stranger, the opportunity to have delicious ice cream, or support from a friend (Haber & Knutson, 2010).

What is unique about the human brain when compared with the brains of other mammals is the size of our neocortex, which consists of the layers of neurons on top of older regions of the brain, such as the amygdala. Significant areas of the neocortex are involved in reasoning, abstract thought, and memory. Some of these regions are particularly involved in social behavior. For example, some regions are involved in self-awareness (D. D. Wagner, Haxby, & Heatherton, 2012) and moral judgment concerning what is right and wrong and whether to punish or forgive (J. D. Greene, 2014). There is also an empathy network of the neocortex that enables us to experience the feelings of others (Singer & Klimecki, 2014) and a “mentalizing network” that enables us to understand other people’s mental states, intentions, desires, and beliefs (Lieberman, 2007, 2013). People feel dramatically different when they are around people who accept them versus those who reject or shun them. It’s not surprising that acceptance and rejection activate much different regions of the brain, known as the social safety and social alarm networks (Eisenberger, 2016; Muscatell & Eisenberger, 2012).

These advances by social neuroscientists set the stage for answers to intriguing questions, such as why gaining power so often leads to its abuse or why people experience a warm glow when they cooperate with others. These discoveries have also provided a window into the development of social behavior by tracing physical changes in the brain. For example, it turns out that a region of the brain that alerts people to danger is poorly developed until early adulthood (Decety & Michalska, 2010). This late development of an important brain region may help explain why adolescents take greater risks (in how they drive, for instance) than people in their mid 20s and beyond.

Neuroscience not only tells us which areas of the brain function most when certain kinds of activities are taking place. It also informs us about how the brain, the mind, and behavior function as a unit and how social factors influence each of these components at the same time.