Behave: The Biology of Humans at Our Best and Worst

Now that we see how brain development impacts adolescent behavior, we work back further to brain development in utero and infancy. This chapter primarily focuses on a field of psychology known as developmental psychology: the study of how the brain changes as we age.

Cognitive Development in Childhood

A few weeks after conception, a wave of neurons is born in the embryo. At 20 weeks, synapses between neurons begin to form. From here, brain development progresses in several stages, continuing well after birth.

To understand how we develop psychologically over time, Sapolsky cites Piaget’s four stages of cognitive development. Piaget is the father of the field of developmental psychology, and his “four stages” is the classic model for understanding how the complexity of our thought changes as we grow up.

In toddler years, we first begin to realize we are separate from others, forming “ego boundaries.” Around nine months old, we also develop Theory of Mind (ToM), the understanding that others have different knowledge than ourselves. ToM slowly develops toward the understanding that individuals have different feelings. Empathy then begins, with perspective-taking channeled through your own motor and pain production systems—that would hurt me, they must be in pain—which gives way to understanding emotional pain. Here, Sapolsky shows how a complex cognitive event—feeling someone else’s pain—is in fact a synthesis of smaller independent abilities (ego boundaries, ToM, and perspective-taking).

Young children exhibit egalitarianism but only within in-groups. A rudimentary sense of justice, first through need for fairness from others for ourselves (around ages 4-6) and then of others for others (ages 8-10) also develops in childhood. Following this, egalitarian childhood tendencies give way to merit-based adjudications in adolescence: not everyone should get the same, you should get what you deserve.

With ToM, empathy and justice in place, we begin to develop our sense of right and wrong. Now Sapolsky cites another developmental theorist, this one more interested in how our understanding of morality change as we age: Lawrence Kohlberg and his “stages of moral development.” Kohlberg’s model is a popular one of developmental morality but has problems. For instance, different cultures have different moral values, and moral appraisals are often emotional, not cognitive, as this model emphasizes. Finally, actually taking moral action is not clearly related to moral cognition.

Above, Sapolsky has demonstrated how human ability for complex cognitive tasks changes as we grow up. Just as differences in brain development inform us why young children behave differently than teens, these examples of childhood brain development help explain why children think and act so differently than adults. It is not just that they have not learned to act with the maturity of adults, it is because their brains are actually different.

Sapolsky now turns to perhaps the second-most famous experiment he will cite in Behave (the first being Zimbardo’s Stanford Prison Experiment in Chapter 12). This is Walter Mischel’s famous series of “marshmallow” experiments conducted in the 1960s. These experiments investigated the ability of children to delay gratification. Mischel placed marshmallows in front of children, telling them if they do not eat the marshmallow, they could have two when he returned, then left the room for 15 minutes. About one-third of children made it to a 15-minute mark. The other two-thirds lasted anywhere from a few seconds to almost all the way. The most important predictor of success was the strategies the children used for coping. Strategies of self-distraction, or thinking about something else, worked best to make it to 15 minutes; eventually, you just forget about the marshmallow.

Naturally, considering the content covered above, older children tended to do better on the test. But the study’s most important finding emerged only years later, when the children were followed up with (a form of scientific study referred to as “longitudinal,” meaning over a long time). In follow-ups 15 years later, Mischel found those who could delay gratification longer did better on their SATs in high school. Forty years later, those who did better had better pre-frontal function and were in better shape. Though Sapolsky leaves this study here, the core of what this finding represents is crucial: Our ability to delay gratification predicts our overall life success. This ability may not only emerge from the strategies we use but may also be innate to our personality type.

Impact of Childhood Experience on Behavior

In perhaps the most heart-rending portion of his book, Sapolsky covers the science of how our early childhood experiences, particularly negative early childhood experiences, shape our behavior throughout our lives.

This starts off with a history of a major blunder in modern science. Infant physical contact with mother figures is crucial for psychic development. However, in the early 20th century, medical science had progressed to a point of unparalleled advancement but had done so through styles of thinking that emphasized the mechanical, not the emotional. Disregarding the need of infants for love from their mother, the parturition industry engaged protocols of separation of infants from mothers for care that today we would find horrific.

It took some experiments with rhesus monkeys to prove how wrong the medical industry was (another example of how important interdisciplinarity is in science as well as of the fallibility of science). Experiments with rhesus monkeys showed infants will often choose a fake mother made from chicken wire wrapped in a terry cloth approximating fur over a fake wire mother with no fur but a bottle of milk because the monkey physically needs love even more than it needs food.

Rhesus monkeys isolated from their mothers in early life stages and later placed in groups show highly fearful and isolated behaviors or exhibit normal instinctual behaviors but at inappropriate times or to inappropriate group members. This shows that mothers are our doorway into social learning: they are the first to show us when actions are appropriate and inappropriate. This helps explain why parental abuse or neglect is such a strong predictor of adult criminality.

Further research indicates that when a fake rhesus mother blasts air or noise at the infant, the infant clings to them harder. When an infant rat has been successfully conditioned to associate an odor with electrical shock, the presence of their mother changes their avoidance of the odor to attraction. These results exist because stress hormones are blocked in infancy to facilitate bonding to the parent, even when the parent is the one causing the stress. This can help explain bonding to abusive parents in humans and, coupled with the parent’s role in teaching sociality, the repetition of these patterns of toxic attachment later in life. Although Sapolsky wrote somewhat dismissively of it above, both of these applications of experiments done on animals to the science of human behavior are an example of the universalist thinking about behavior typical of behaviorism (see Chapter 3). In another lens, however, they have more to do with the unique capacity for social learning available to primates, suggesting a more ethological moral.

Other forms of childhood adversity that cause chronic stress, such as paternal deprivation, poverty, and bullying, have similar negative effects in adult life: we seek out or enact these negative situations because this is how we were taught to behave by our parental models. They become our “safe spaces.” Importantly, most people who experience some adversity in childhood emerge as functional adults. It is individuals who experience repeated and diverse adversities and abuses in childhood that are most at risk.

Different parenting styles also impact adult behavior. Authoritative parenting, in which rules are consistent, clear, and explicable, produces happy, emotionally stable children and adults. Authoritarian parenting, in which rules are numerous and arbitrary, produces obedient, conformist, unhappy and potentially explosive adults. Permissive parenting, in which there are few and rarely enforced rules, produce self-indulgent adults with poor impulse control and social skills. As Sapolsky outlines, these parenting styles tend to map onto socioeconomic levels, with the rich generally the most permissive in their parental styles.

Though we all progress through stages of cognitive and potentially moral development in childhood, the myriad circumstances of our childhood, including the presence of parental love, overall parenting style, chronic stress and social learning factors, have huge effects on our lifetime patterns of behavior.

The major takeaway of this chapter is its opportunity to reflect on how we tend to think of the science of behavior. When a topic, such as hormonal signaling, exists in a clearly scientific domain, we tend to think of it as having a simple, deterministic effect on us. For instance, we think testosterone as a chemical that makes us more aggressive. The truth, however, is not that simple. Hormone effects depend on the contexts of individual species’ evolution and the nature of the immediately triggering events experienced by the organism, as Chapter 3 showed. The opposite is true of how we tend to think of things that exist outside of clearly scientific domains, like the emotional effects of parental abuse. These, we think, are soft-sciences, or non-scientific: They have effects, but those effects are emotional and psychological, not necessarily physically represented in the brain. This is also not the case. Though their causal factors may be more complex, they are no less scientific and no less open to scientific inquiry. Understanding human behavior means bringing these seemingly non-scientific topics into the scientific purview.