We Are Our Brains (6 page)

That protective role of the male isn't confined to primates but extends to the entire animal kingdom. A pair of coots have once again built a large nest in the middle of the canal opposite our house. From the moment that the female started to sit on the nest, the male became incredibly aggressive toward any other birds in the vicinity. Not a single egg had yet been laid, but the coot managed to scare off much larger crows and ducks with a great deal of noise and flapping of wings.

A man, too, is prepared for his role as a father during his partner's pregnancy. Hormonal changes take place that affect the brain, making prospective fathers not only behave differently but also feel differently. Even before the child is born, the father's prolactin level increases. That hormone is important for the mother's milk production, but in both women and men it stimulates caring behavior. Conversely, the father-to-be's level of the male sex hormone testosterone declines, reducing aggression toward the child and the urge to procreate—a universal mechanism that affects prospective fathers from New York to Beijing. As a result, even before their child is born, many men feel that something special is happening to them. How those behavioral changes are induced isn't clear, but scents given off by the pregnant partner may play a role. After the birth, prolactin and oxytocin play a role in paternal behavior and bonding between father and child. When playing with their children, an increase in the bonding hormone oxytocin is seen only in fathers who display affectionate and nurturing behavior.

In some animal species, the father has been allotted an extreme role. In the case of the Greater Rhea, an ostrich-like bird, the males incubate the eggs in a nest that they have scraped out themselves, while male seahorses carry their eggs in a pouch until they hatch. Caring paternal behavior comparable to that of humans is seen in a few
other species, allowing us to study the changes in the brain that provoke it. Marmoset fathers look after their offspring by carrying them, protecting them, and feeding them. Fatherhood induces changes in the prefrontal cortex. The number of synapses in this area of the brain increases, suggesting a reorganization of the local network. It also becomes more sensitive to vasopressin, the chemical messenger that promotes social behavior and aids fathers in their new tasks.

As children grow up, their fathers may inspire them and affect the course of their lives. This can take many different forms. My grandfather was a doctor, and he succeeded in interesting his son in his profession. My father became a gynecologist, and I knew from the age of six that I would study medicine. My son was uncertain about his choice of studies for a long time, but he knew from an early age that it would not be medicine or biology. He, too, was reacting to his father, albeit in a different way. We later discovered a shared interest in behavioral differences between the sexes and both published findings on this subject (see
chapter 21
).

Alas, the father's role doesn't confine itself to noble actions like care, protection, and inspiration. Examples of the primitive aggression that males are capable of in the name of fatherhood are common both in the animal kingdom and among humans. Male primates can take over an entire harem of females from another group by chasing away the dominant male. As a rule, they then kill all the young. When a lion takes over a pride of lions, he kills the cubs, despite the lioness's desperate attempts to defend them. This stops her milk production, making her fertile more quickly, ensuring that her young are the offspring of the new dominant male. And human history shows us to be no exception, to judge by what we read in the Bible: “But Moses was angry with the officers of the army, with the captains … who had come from the battle [and] said to them: ‘… Now therefore, kill every male among the little ones, and kill every woman who has known a man intimately. But keep alive for yourselves all the young girls who have not known a man intimately' ” (Numbers 31:14–18).

Even in this day and age, we haven't yet managed to escape these cruel biological mechanisms. Infanticide and child abuse are more commonly perpetrated by stepfathers than biological fathers, and children of women captured during wars are still regularly killed. Female chimpanzees keep far away from groups of other chimpanzees for years after giving birth—a good strategy for ensuring that their young aren't killed by males who doubt their paternity. The “solution” devised by bonobo females to prevent infanticide is an original one. They mate with all males, so that no single male can ever be certain that he's not a youngster's father. But in the case of humans, mothers must remain vigilant, alert to all the dangers that
might threaten their children—a state they remain in for the rest of their lives.

FIGURE 6.
A synapse as seen under an electron microscope. Oxytocin and vasopressin appear as black granules. When released in the brain, these substances influence behaviors—for instance, social interaction. From Buijs and Swaab,
Cell Tiss. Res.
204 (1979): 355–65.

You come into the world with a brain that your genetic background and your development in the womb have made unique and in which your character, talents, and restrictions have largely been determined (see
chapters 3
and
8
). For the brain to grow optimally after birth, the developing child needs a safe, stimulating environment that imposes achievable demands on it. Back in 1871, Darwin had already found that the brains of hares and rabbits that grew up confined in boring hutches were 15 to 30 percent smaller than those of their wild counterparts. Conversely, when animals are placed in an “enriched environment,” a large enclosure full of objects that are renewed each day and in which they can play with one another, their brains grow and develop more synapses. Children who are seriously neglected during their early development also have smaller brains (
fig. 7
); their intelligence and linguistic and fine motor control are permanently impaired, and they are impulsive and hyperactive. Their prefrontal cortices can be particularly undersized. Studies have shown that orphans adopted before the age of two go on to develop normal IQs (averaging 100), while children who are not adopted until between the ages of two and six attain average IQs of 80.

The American child psychiatrist Bruce Perry described the case of a grossly neglected six-year-old boy named Justin, who lost his mother and grandmother as a baby and grew up in the care of a dog breeder, who treated him like one of his dogs, keeping him in a cage. He made sure that Justin was fed and changed, but he hardly spoke
to him and never cuddled him or played with him. When Justin was later hospitalized, he was unable to speak or walk. He threw his feces at the medical staff. A scan showed his brain to be much too small; it resembled that of someone with Alzheimer's. In the stimulating environment of a foster family, he started to develop, and by the age of eight was able to go to nursery school. It isn't known what lasting damage he has suffered.

In his book
Émile; or, On Education
, published in 1778, the Enlightenment philosopher Jean-Jacques Rousseau (1712–1778) set out his theory of the “noble savage.” He believed that children were innately good but were subsequently corrupted by society. However, interaction with one's surroundings is necessary for normal brain development, as is clear from Justin's story and the well-documented tale of the Wild Boy of Aveyron, a feral child discovered in the woods of the region of Languedoc in southern France in 1797. It took three full years before the child was captured by hunters and brought to the local town. At the time he was around ten; having been abandoned at a very young age, he had kept himself alive on a diet of fruit and small animals. A young doctor, Jean Marc Gaspard Itard, took on the task of educating the boy (whom he named Victor), sending lengthy reports on his progress to the French government department for internal affairs. Despite Dr. Itard's best efforts, Victor never developed fully as a person, and the only word he learned to say was
lait
(milk). It makes one wonder about the achievements of those other famous feral children, Romulus and Remus.

The acquisition of our mother tongue also shows how certain brain systems continue to be programmed by the environment after birth. A child's first language isn't determined by its genetic background, only by the surroundings in which it grows up during that critical period of language acquisition. Not only does acquiring language have a very marked effect on the brain, it's also crucial to many other aspects of a child's development. In 1211, the Holy Roman Emperor Frederick II of Germany, Italy, Burgundy, and Sicily tried to establish what language God spoke to Adam and Eve. He
believed that children would spontaneously speak it if they were not exposed to other languages and set up a rigorous experiment in which dozens of children were brought up by nurses ordered never to speak to them. However, his hopes were met with disappointment. The children couldn't speak at all, and they all died at a young age. Likewise, one in three orphans brought up in severely understaffed children's homes in World War II died from the consequences of physical and emotional neglect, and those who survived were psychologically scarred. So proper interaction with one's surroundings isn't just a precondition for normal brain development, it's actually crucial to survival.

During the first few years after birth, our surroundings determine the configuration of the brain's language systems. After a certain critical period these systems become fixed. Any attempts to learn a second language are made with, say, Romanian, Uzbek, Dutch, or Italian brains, causing us to speak with an accent. In children between the ages of nine and eleven, the brain areas that process words and visual information still overlap. By adulthood, specialization has taken place, and the two types of information are processed in separate areas. The language environment creates permanent differences in brain structures and functions. Depending on whether your mother tongue is Japanese or a Western language, vowels and animal sounds are processed in the left or right cortex, irrespective of your genetic origins. The frontal cortex is the site of Broca's area, which is crucial for language (
fig. 8
). When adults learn a second language, another sub-area of this region is involved. But if children are brought up bilingually from an early age, both languages use the same frontal areas. In such cases, the left caudate nucleus (
fig. 27
) checks which language system is being used.

Our linguistic and cultural environments don't determine only which brain systems are involved in language processing but also how facial expressions are interpreted and how we scan images and their surroundings. Japanese and New Guineans, for instance, find it difficult to distinguish between a face expressing fear and a face expressing
surprise. When surveying a scene, Chinese individuals, unlike Americans, don't focus on a single object at a time but look at it in relation to its surroundings. When doing mental arithmetic, the Chinese use different parts of the brain than Western Anglophones. Both use the same Arabic numerals and the lower region of the parietal lobe (
fig. 1
), but English speakers make more use of language systems to process numbers, while Chinese speakers make more use of visual motor systems. This can be explained by the fact that Chinese grow up learning characters. (The Chinese abacus is no longer so influential in modern China.)

The notion that the environment stimulates brain development was suggested early on by Maria Montessori, who discovered a link between socioeconomic environment and brain development, which she described in her
Handbook
(1913). Socioeconomic status is also an important factor in stimulating the development of children with a disadvantage, like being underweight at birth. A highly stimulating “enriched” environment promotes recovery after a developmental brain disorder. Studies have shown that children whose early development is disrupted by malnourishment or emotional neglect can improve radically if placed in a more stimulating environment early on. Children with Down syndrome, too, respond well to intense stimulation in their environment. So children with learning disorders should not be incarcerated in institutions where they receive little stimulation. On the contrary, they have an extra need for stimulus, which will positively affect the rest of their lives.