The Triune Brain: Evolutionary Foundations for Human Goodness

“A human being is a part of the whole, called by us Universe, a part limited in time and space. He experiences himself, his thoughts and feelings as something separated from the rest — a kind of optical delusion of his consciousness. This delusion is a kind of prison, restricting us to our personal desires and to affection for a few persons nearest to us. Our task must be to free from this prison by widening our circle of compassion to embrace all living creatures and the whole nature in its beauty.” Albert Einstein

Humans are remarkable in their scope and scale of cooperation. By contrast to nonhuman animals, we are willing to share resources and information with each others, we are capable of experiencing complex social emotions (e.g., pride, awe, elevation, guilt, etc) and committing to collectively shared goals; we are able to delay immediate gratification to reap larger collective benefits in a distant future. Moreover, experiments in behavioral economics show that a substantial majority of people are averse to unfair or inequitable distribution of resources; they are willing to incur personal costs to punish others for their violation of social norms and free-riding.

The prosocial tendencies “when people act in ways that benefit others” can already be observed in young one-year-old children who “display spontaneous helping behaviors when another person is unable to achieve his goal” without any expectation of rewards or reputational benefits. Researchers argue that this predisposition for doing good was likely to occur in humans “preculturally”, before the emergence of social norms, so that “human cultures cultivate rather than implant altruism in the human psyche.”

Since altruism is “a central organizing principle” for complex social organisms and organizations (group-living mammals, insect societies, trees, etc), it is important to understand its evolutionary origins and neurobiological underpinnings to assure its critical regulatory function for sustainability of our global society.

One of the best way to trace the evolution of altruism — its progression from simple to more complex forms — is to look at the evolutionary structure of the human brain and the increasing sophistication of human emotion. The evolutionary model of human brain — also known as the triune brain model — has been developed by american physician and neurobiologist Paul MacLean in the 1950–1960.

According to the triune brain theory, a human brain can be represented as a hierarchical structure composed of three interdependent layers:

I. Reptilian brain

The reptilian brain (including the brain stem, cerebellum and basal ganglia) is the most ancient brain structure responsible for automatic life-support functions such as breathing, heart beating, temperature regulation, motor functions, balance, feeding, sexuality, and territoriality. These genetically encoded reflexes are critical for an organism’s survival and can be found in all vertebrates.

While often associated with a reptilian cannibalism or other forms of anti-social behavior (dominance, aggression, etc.), the neuroanatomy of reptilian brain is sufficient enough to enable the simplest forms of altruism and social organization. For example, insect societies (e.g., ant colonies, beehives, termites, etc.) display complex social structures which emerge thanks to altruistic behaviors of its cognitively limited members. The basic forms of altruism include:

• Kin-based altruism generally takes place among genetically related members of the same group, family or colony when individuals can identify and detect a biological kin via the mechanism of social recognition. For example, social insects rely upon chemical signals (colony odor recognition) to identify their nestmates with whom they engage in group-level activities such as food provisioning or a nest defense against enemies; mammals use a more complex evaluation of the kinship relations based on the frequency of a target’s presence during a sensitive period of parental care.
• Coercion-based altruism operates via the mechanism of social control and pressure. For example, insect societies promote altruism by hindering direct reproduction of their workers (e.g., the killing of worker-laid eggs or preventing larvae from developing into queens via food control). In vertebrate groups, enforced altruism has been observed in various forms: monkeys punish individuals who do not share food; cichlid fish evict members of their community who don’t help or share food; in meerkats the dominant female suppresses the reproduction of subordinates.

These biologically oldest forms of altruism are instinctive or sensory-driven. They rely upon “primordial affect” of the reptilian brain that register comfort or discomfort, “the ‘error’ signals — both good and bad deviations from homodynamic states of balance. Balance within and between body and world, within and between mind and body, and ultimately within and between individuals comprising social bodies.” This kind of balance (or homeostasis) is critical for assuring the integrity of social groups and their survival over time and can be achieved via biologically-driven altruism.

II. Mammalian brain

The mammalian brain, also known as the limbic system (including the amygdala, hippocampus and hypothalamus) appeared later in biological evolution and it is associated with “the development of hearing, vocalization and protracted parental care” in mammals. The limbic system has evolved to process and express a wider array of emotions (fear, anger, joy, grief) that enabled “the full expression of maternal behavior and the capacity for play”. As MacLean put it, there are three key behavioral advances that marks the evolutionary shift from reptiles to mammals: nursing; parental care; and play. “The history of the evolution of mammals is to a large extent the history of the evolution of the family.”

Because of its critical role in supporting parental care, the mammalian brain gave rise to empathy-based altruism or empathic concern — the other-oriented altruistic behaviors in response to another individual’s distress, pain or need. Empathic concern and care about the welfare of others are possible thanks to the limbic brain’s capacity to perceive an internal emotional state of others and form shared representations. This automatic unconscious mechanism of state-matching help us to better understand and predict others’ feelings, motivations and actions.

Empathy is widespread in the animal kingdom, ranging from emotional contagion in birds’ flocks to consolation, empathic perspective taking and targeted helping in large-brain apes and humans. Depending on the brain size and complexity of cognition, empathy-based altruism can take more or less sophisticated forms. For example, both young children and chimpanzees display spontaneous, unrewarded helping behavior when they perceive the others’ need for help but human children perform better in cognitively demanding ‘out-of-reach’ tasks where chimpanzees “don’t know how to intervene.”

Empathy-based altruism is intrinsically rewarding and “derives its strength from the emotional stake it offers the self in the other’s welfare, i.e., helping the other ameliorates the helper’s internal state.” This “doing good — feeling good” connection might explain some costly helping behavior in animals and humans (e.g., risking our own life for saving others) when the benefits of altruistic behavior are far beyond the altruist’s cognitive horizon.

While kin-based altruism of the reptilian brain requires some genetic commonality, empathic altruism of the mammalian brain is more likely to occur among individuals who share some “similarity, familiarity, social closeness, and positive experience” with each other. In other words, contextual appraisal such as perceived fairness or group membership of others might amplify or reverse empathic response, that is, individuals will empathize with those whom they perceive as fair, cooperative or from “the same boat” but will display an antipathic response to their competitors, outsiders or previous defectors.

III. Neocortex

The neocortex (cerebral or prefrontal cortex) is the most recently evolved and the largest part of the human brain that accounts for over 80% of brain mass . It is responsible for human higher-order cognition such as planning for future, abstract thought, language, creativity (arts, music, science, etc.), ethical principles and self-discipline.

These superior cognitive abilities in humans became possible thanks to the brain’s lateralization (differentiation) into two hemisphere: left vs. right. The “lateralization has developed in order to make room for new skills without the loss of existing skills. Lateralization makes room for additional skills because functions can be divided between the right and left hemisphere, and the two hemispheres are free to specialize in different functions.”

The left hemisphere is known as the explicit verbal part of the brain “specialized in language production, cognitive analysis, logical conclusions, and the perception of details.” It is important for human ability to codify social information that can be transferred from person to person, from generation to generation. While the “left hemisphere is capable of differentiating, analyzing, and sequencing, the right hemisphere — the implicit non-verbal part of the brain — is spatial, holistic, and integrative.” It is responsible for human emotional communication, motivation, self-regulation, and stress-coping strategies.

The right hemisphere is dominant for human mental health and socially adaptive behavior since it is hierarchically integrated with the deeper, evolutionary ancient layers of the brain (mammalian and reptilian) and thus assures a two-way communication between body (emotion) and mind (reason). The bottom-up communication provides energy and motivation for higher-order cognitive activities, while the top-down flow assures control and regulation over bodily animal-like states and behavior.

Source: Adapted from Schore (2011).

The right hemisphere is the seat of complex (the less time urgent) emotions such as pride, elevation, gratitude, compassion, guilt, shame, admiration, etc. which are essential for “self-control,” “self-discipline,” or “grit,” all of which describe the ability to endure short-term pain in order to cultivate long-term, complex — highly meaningful — pleasure.” Complex feelings and emotions “serve the self-developmental imperative, and are goal-relevant to the “higher” human needs — needs for enduring social bonds, for self-esteem, for creativity, and long term meaning.”

While being very different in their functions and nature, the two brain hemispheres complement each other, and cannot exist without each other’s functions. The functional integration between the logical, linguistic left hemisphere and the holistic, emotional right hemisphere is crucial for cooperation-based altruism when individuals subordinate their personal needs to higher-order collective goals. Commitment to shared goals — abstract, long-term visions for future — allow human individuals to delay immediate gratification and experience complex positive emotions (elevation, pride, compassion, etc.) associated with human health, creativity and longevity.

This intricate combination of cognitive and motivational mechanisms in the human neocortex — that underlies our willingness and “ability to participate in collaborative activities with shared goals and intentions” — have been recognized as the fundamental source for the majority of our unique human achievements such as language, complex technologies, science, arts, ethics, social norms and institutions, religion and “the formation of large, structurally complex societies such as states.”

Conclusion

The evolutionary history of the human brain and human emotion demonstrates that human brains are “hard-wired for social connection” and prosocial altruistic behaviors. The brain progression from “primordial” affect (pain/pleasure sensations) towards complex feelings and emotions enabled the expression of the most complex cooperative behaviors in humans which are critical for welfare and sustainability of our human society.

Our analysis, however, suggests that some kind of commonness or common ground is required to activate these evolutionary adaptive mechanisms: shared genes are necessary for kin-based altruism, shared representations of emotional states generate empathy-based altruism, whereas shared goals lay the ground for cooperative human behavior.

While kinship relations are genetically given (fixed), the enabling conditions for human empathy and cooperation are more malleable and vulnerable to social influence and contextual appraisal. When government and social media emphasize racial or national differences, genetic predisposition for poverty (and not social causes), or business schools indoctrinate future managers and leaders with economic beliefs in selfishness, competition and greed, then this large-scale propaganda distorts people’s perceptions of reality and might lead to collective dehumanization and socially destructive human behaviors (e.g., wars, ethnic and social conflicts, corporate misbehavior and major business failures).

This article was originally published on my blog. I would be grateful for any kind of constructive feedback and comments.