The Social Brain and Human Evolution

Samuel Taylor Coleridge, an English poet, pointed out that a tiger remains the same whether it lives alone or among thousands of other tigers. A tiger is just a tiger. But humans are unique. According to Coleridge, our relationships with others change us in fundamental ways. Without these connections, we wouldn't develop skills like understanding emotions or picking up on social cues. Today, this concept is called the "social brain."

When people casually refer to the brain, they usually mean it as a single unit. However, neuroscientists explain that we have a "triune brain," which means three brains in one. These three parts represent different stages of evolution. 

• The first part called the reptilian brain developed early and is centered around basic survival functions like breathing and heartbeat. 
• The second part, the mammalian brain, formed around the reptilian core and introduced emotions, enabling behaviors like caring for offspring. 
• Finally, the outer layer called the cerebral cortex emerged.

The cerebral cortex is where the social brain developed, making us distinctly human. It helps us manage emotions, follow social rules, and feel empathy. Thanks to this part of the brain, humans don’t just react to basic emotions like fear or anger. Instead, we can experience a wide range of feelings, such as sadness, guilt, love, or joy. While most mammals might experience life in simple terms, the social brain allows humans to understand the world with much more depth and complexity. Interestingly, when a baby is born, its brain is already equipped with several systems needed for survival. It can breathe, sense temperature changes, see movement, and respond to stimuli through a basic form of awareness. However, the social brain isn’t developed at birth.

How a Baby's Brain Develops and Why Early Experiences Matter

Parents know that babies can be tough. Sometimes they cry nonstop or refuse to eat the vegetables you've been offering for half an hour. Yelling, bargaining, or using discipline doesn't help because babies can’t yet control their behavior. A baby can’t think about their parents' frustration or eat their carrots to make them happy. This is because a key part of their brain called the orbitofrontal cortex isn’t fully developed yet. This part of the brain helps with emotional intelligence, as Daniel Goleman explains. Without it, social skills are difficult to develop.

People with damage to this area of the brain often struggle to understand social and emotional cues, and may even show signs of sociopathy. However, the orbitofrontal cortex doesn’t develop on its own. It grows through the experiences a baby has during the first few years of life. Researchers call this “experience dependency,” meaning a baby’s brain builds itself based on its surroundings. This allows babies to learn and adjust to the culture they’re born into.

However, since a baby’s brain is so flexible, it can also be easily damaged. In a famous experiment in the 1930s, researcher Harry Harlow found that if a monkey is isolated for the first year of its life, it will become almost unable to interact with others. Harlow concluded that social interaction is necessary for developing social skills. More recently, researchers in Romania studied the brains of three-year-olds who had lived in orphanages and were neglected with little adult interaction. Brain scans showed large gaps where the orbitofrontal cortex should have been. This shows that a lack of social contact during the first few years can cause permanent damage to the brain.

The Role of Pleasure in Baby’s Development
Before babies can learn about human culture, they need to be invited to join it. This invitation comes through two connected parts: the behavior of caregivers and the chemicals in the baby's brain. Together, these make social interactions enjoyable.

As long as parents enjoy their time with their babies, there's no need for concern. This is because enjoyable interactions help a baby’s brain grow and set the stage for emotional control later in life. This happens because of how pleasure activates the orbitofrontal cortex. The first kind of pleasure a baby experiences is from touch. Being gently held by their father in a warm and safe environment causes the baby to relax. Their breathing becomes deeper, and slowly their heart rate and nervous system match with their father’s. These are basic parts of human culture. They explain why we hug grieving people to comfort them or why sex is a way to bond with a partner. They also explain why a good massage can relieve stress so well. Another source of pleasure is looking.

When a baby looks into their mother's eyes, they can see her pupils expand, showing that her body is experiencing positive feelings. This makes the baby’s nervous system react the same way, starting a chain of chemical reactions. As the baby’s heart rate increases, the brain releases chemicals called beta-endorphins. These not only bring pleasure but also help control blood sugar, which in turn helps the brain grow. At the same time, another chemical, dopamine, is released in the brain, which helps the brain grow even more. This complex process at the microscopic level has a simple purpose: it makes looking into a parent's eyes enjoyable. The more a baby does this, the more their social brain develops.

Brain Development and the Role of Experience

The way a building is built is just as important as the architect’s plan, and the same goes for the brain. While a baby is born with all the neurons she will ever have—decided by her genes—those neurons need to be connected. This process happens during the baby’s first year, outside the womb. The final structure of the brain depends on both genetic and social factors.

Between 6 to 12 months, the baby’s brain forms a dense network of cognitive possibilities. This is the foundation for the mind, but the process isn't finished yet. After this stage, the brain begins to shrink in a process called pruning. This means that brain cells that aren't used often start to die off. In other words, the brain keeps the connections that are helpful and gets rid of those that aren’t.

So, what makes a connection useful? According to neuroscientist Daniel Siegel, the brain works like a machine that predicts what will happen next to help us navigate the world. As the baby starts to recognize patterns in her interactions with others, her brain stores the information that helps her understand the world. For example, if the baby’s mother always wrinkles her nose in disgust when changing her diaper, the baby starts to expect that diaper changes are unpleasant. This information gets stored in her brain because it’s useful. On the other hand, if the mother wrinkles her nose randomly, with no clear pattern, this information isn't useful and gets discarded.

Stress and Its Effects

Stress is a term we often link to things like long work hours or a tough day at the office. It can also come from worrying about basic needs, like how to pay for food or rent. Even though stress can stem from various sources, it often feels overwhelming. Many people think stress is just a part of adult life, tied to paying bills and managing a family.
But stress affects us throughout our lives. It’s an ancient survival mechanism. Our ancestors faced real dangers, like hungry predators. When they encounter threats, their brains release a hormone called cortisol. This hormone acted like an alarm, telling their bodies to focus on the emergency and deal with the danger.
Modern society is much safer—few of us face dangerous predators today. However, our survival still depends on social acceptance and status. When these are threatened, our stress response kicks in.

• Short-Term Benefits Cortisol, the stress hormone, is useful in the short term. It helps break down fats and proteins to provide extra energy, which can be helpful if you need to work late or face a tough situation.
• Long-Term Issues Problems arise if cortisol levels remain high for too long. Chronic high cortisol can weaken the immune system, making people more likely to get sick.
• Managing Stress Adults can handle stress through various methods, such as getting massages, socializing, or seeking professional help.
• Impact on Babies Babies can’t manage stress on their own. If parents don’t control their stress levels, it can lead to high stress in babies, potentially causing long-term harm.

Stressful Situations and Their Commonality
Imagine you're picking berries in the forest and suddenly find yourself face-to-face with a dangerous animal. Or think about being low on money but still able to pay your rent, only to get an unexpected bill that leaves you short on cash with just one day to fix it. Both situations are stressful, and they share something important: they're both unpredictable and out of your control. Since a baby’s entire life is full of unpredictability and lack of control, it makes sense that this can be a very stressful time for her!
Babies rely completely on caregivers for survival, as they can't feed, protect, or keep themselves warm. They can only cry for help, and when ignored, they feel helpless. Separation from caregivers triggers the release of a hormone called corticotropin-releasing factor (CRF), often referred to as the "fear hormone." This hormone can make even short separations from caregivers very scary for babies. Cortisol, another hormone, increases in young mammals separated from their mothers. A 2002 study in Biological Psychiatry showed that squirrel monkeys separated from their mothers had higher cortisol levels. Repeated separations, even for just five hours a week, made the monkeys more clingy, easily distressed, and less playful.
Research suggests that high cortisol levels during infancy might have lasting effects on humans. A study from 2000 showed that early exposure to cortisol was linked to a lower number of cortisol receptors later in life. These receptors help regulate cortisol levels, so fewer receptors make it harder to manage stress. Interestingly, babies who experienced neglect and were rarely held had fewer cortisol receptors. In contrast, babies who were frequently touched and held had more receptors, indicating better stress management as they grew up. This implies that lower cortisol exposure in infancy leads to better stress management abilities later in life.
Parental Presence and Children
A mother's absence can significantly affect her baby's biochemistry, but the quality of her presence is just as crucial. This issue arises when a baby lives with biological parents who either provide poor care or are mentally unavailable despite being physically present. For example, research shows that children of parents with alcohol addiction have higher cortisol levels compared to those whose parents do not have this issue. This elevated stress hormone level is also found in the parents themselves.
In a 1994 study published in Biological Psychiatry, researchers examined how unpredictable food sources affected monkeys. They found that when mother monkeys couldn't predict where their next meal would come from, it caused them more stress than consistently having too little food. This stress didn't just impact the mothers; it also affected their offspring. The young monkeys experienced high levels of stress hormones, indicating they were stressed too. The researchers concluded that the mothers' preoccupation with finding food left them unavailable to comfort their children, causing the young monkeys to remain in a constant state of anxiety.
Does this apply to humans? Possibly. A significant piece of evidence comes from a 2002 study by psychologist Marilyn Essex at the University of Wisconsin. Essex tracked 570 families over five years, from their children's birth until their fifth birthdays, and regularly measured stress levels in both parents and children. 
She found that at four and a half years old, children living with stressed mothers had high cortisol levels, but only if their mothers had also been stressed during the children's infancy. In other words, children were more vulnerable to stress if they experienced a stressful early life. These findings suggest that children who face early stress may produce more cortisol when stressed compared to those with calmer babyhoods. As they grow, they may struggle more with handling challenges due to the lingering effects of early stress.
Early Life Experiences and Stress Response
If a baby's early life is calm and loving, it helps their brain develop more cortisol receptors, which are important for managing stress. These receptors help the brain regulate cortisol levels, reducing stress and preventing long-term damage. However, if a baby experiences a lot of stress or discomfort early on, their brain might develop an overactive stress response. This leads to high cortisol levels, causing constant stress. Over time, this can increase the risk of anxiety and depression in adulthood. A brain with many cortisol receptors can effectively handle stress hormones and stop producing cortisol when it's not needed. But a brain lacking this protection may struggle, with cortisol levels remaining high and causing potential long-term harm.
Lack of positive social interaction can hinder the development of the social brain. This can lead to reduced production of norepinephrine, a chemical that helps us concentrate and maintain effort. Adults with depression often have low norepinephrine levels, making it difficult for them to break harmful habits. Social deprivation in infancy can also permanently reduce dopamine synapses. British biologist Paul Martin, in his book The Sickening Mind, explains that the presence or absence of these synapses influences our outlook on life. 
For example, a child with plenty of dopamine in their orbitofrontal cortex tends to feel positive about new experiences and adapts quickly to challenges. In contrast, a child with fewer dopamine synapses may struggle to focus on rewards, adapt less easily, and be more prone to depression and giving up. This all highlights a crucial point: love matters. The more love and protection we receive as babies, the more likely we are to grow into happy adults.