Behave: The Biology of Humans at Our Best and Worst

Behavior occurs due to messages bouncing around in the brain, but these messages are, in turn, triggered by environmental stimulus. This chapter focuses on how stimulus within and without our bodies trigger behavior.

To foreground this chapter, Sapolsky introduces the history of two different sciences based on the observation of behavior in animals. The first is behaviorism, which “cared about universalities of behavior across species” and “worshipped a doozy of a […] universal” (82): rewarding an organism for a behavior makes the organism more likely to repeat it, while not rewarding or punishing it makes the behavior less likely. Behaviorists, most primarily the field’s major champion B. F. Skinner, saw this fact as so universal they believed any creature (including humans) could be trained to complete any behavior, meaning in turn that all behavior is conditioned.

Sapolsky acknowledges the importance of behaviorism’s scientific findings (behaviorist processes, such as operant conditioning, remain a major form of scientific study of behavior to this day). However, as an alternative to behaviorism, Sapolsky introduces ethology, the study of animal behavior that occurs not in a lab but in the field, which focuses on environmental triggers that produce behavior and is interested in the behaviors of animals that are unique to that species. These can be auditory cues, including hoots and growls, or visual cues, such as gesture or color.

For both animals and humans, many of the sensory cues that influence behavior are subliminal, meaning not consciously processed. In humans, for example, subliminally signaling (flashing it at a speed so fast the subject sees it but does not register seeing it, also known as “priming”) a face of a race separate from the subject predicts higher amygdaloid activation: more fear, more disgust. However, if this face is maintained as a stimulus long enough for conscious perception, the dlPFC also activates to inhibit the amygdala’s aggression or fear response. “It’s the frontal cortex exerting executive control over the deeper darker amygdaloid response” (85). This is an example of doing the right thing, in a moral sense of “right,” despite it being the harder thing to do because such amygdaloid suppression is cognitively taxing for the PFC.

Other studies show similar differences in how individuals respond to subliminal stimulus of races other than themselves. The fusiform gyrus, specialized for face recognition, activates less for faces of other races than our own (86). The reflexive tensing of muscles in response to the pain of others is more prevalent for our own race than others (86). Emotive reaction in the medial PFC for the misfortune of others is higher for those of our own race (86). Neuro-electric threat responses trigger more often for races other than our own, and feedback electrical responses meant to suppress this threat reaction trigger less (86-87). Summarizing this range of results from priming studies, Sapolsky demonstrates one core point: we are reflexively driven toward racist tendencies. This is an example of the moral neutrality of biology: although such aversion to people not visibly like ourselves was the best thing for us in our evolutionary context, today it is an undesirable trait. Understanding that it exists, however, is crucial to addressing it. This is the value of a biological understanding of behavior.

Humans respond to other subliminal cues. The gender of faces is processed in milliseconds, as are dominant vs. submissive postures, and the stereotypical beauty of faces also subliminally influence our judgement on morality and intelligence. Humans can predict political affiliation with above-random accuracy by looking at faces, and men report higher attraction to female faces during ovulation cycles. Each of these are examples of humans receiving and acting on cues that we don’t even know we’re perceiving.

Our brain also picks up information from within our body to influence emotion and behavior. This is called “interoceptive” information. In the 1880s, theorists Henry James and Carl Lange showed that our ANS can in some cases respond to external stimulus faster than our conscious mind, with our conscious mind conforming to the information produced by that autonomic state. Therefore, if we influence the state of our autonomic nervous system, we can influence our emotions. For instance, smiling can automatically make us less sad, and taking dominant postures decreases stress hormone levels. These are examples of our brain reading information from our bodies to inform our mental state without us realizing it is doing so. To recall a chapter above, it is an example of a bottom-up process in the brain (moving from the automatic lower brain to the cognitive upper brain).

All of these sensory cues shape behavior, but in a “wonderfully complicating piece of the story” (96) the brain can alter the sensitivity it has to these signals. This is because the brain not only receives information from organs, but it also sends neuronal projections to organs, which influences their behaviors. This is covered in more depth in future chapters. For now, what remains important is that behavior is caused by messages bouncing around in the brain, but these messages are themselves caused by internal and external stimuli.