5.1 Setting the Context

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The monkeys in this photo reached adulthood at roughly age 7 or 8 (Poirier & Smith, 1974). Why do human preschoolers take twice as long to grow up?

Special Mindreading Skills

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Imagine that these chimps could really share what insights were going on in each other’s minds. Wouldn’t they be inventing the Internet and traveling into outer space?
© Markus Botzek/zefa/Corbis

The reason is that our species has a unique capacity—the ability to build on each generation’s intellectual advances. Three-year-olds born in biblical times had the same biology as today’s preschoolers, but these twenty-first-century children will grow up using iPads and surfing online. They might even take vacations on the moon or Mars.

What talent allowed humanity to mentally take off? Evolutionary theorists believe at the core of our achievements lies our social cognitive capacity to put ourselves in other people’s heads and decode intentions (recall Chapter 3). Monkeys show glimmers of this mindreading ability (see Buttelmann, Call, & Tomasello, 2009); but because they don’t have our language capacities (also described in Chapter 3), our close mammal cousins can’t draw on each other’s insights to transform the world. (“Oh, now I understand what you were trying to do. Let’s work together to improve on that.”) Capitalizing on these insights, in turn, demands a large, slow-growing brain.

Slow-Growing Frontal Lobes

Actually, our huge cerebral cortex takes more than two full decades to mature. The myelin sheath—the fatty neural cover—grows into our twenties. Synaptogenesis (the process of making billions of connections between neurons) is on an extended blossoming and pruning timetable, too, especially in the brain region responsible for thinking through our actions—the frontal lobes.

Figure 5.1, which compares the size of our cortex to that of other species, shows the huge frontal lobes positioned at the top of the brain. During early childhood, the neurons in the visual and motor cortices are in their pruning phase, which explains why vision develops rapidly and why we master basic physical milestones, such as walking, at a relatively young age. However, the frontal lobes are only beginning their synaptic blossoming when we start toddling around. Pruning in this part of the brain will not start until about age 9.

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Figure 5.1: The human cortex and that of some other species: Notice the size of our cortex in comparison to other species. Also notice the dramatic increase in the size of our frontal lobes. It is our mammoth cortex and especially our huge frontal lobes that are responsible for everything that makes our species unique.

Their slow frontal-lobe timetable explains why preschoolers have so much trouble controlling their behavior, and why our ability to plan, think through, and inhibit our actions improves over years. It even accounts for the high expectations we have of elementary schoolers when the frontal lobes enter their pruning phase. We expect fourth and fifth graders to understand long division and take responsibility for completing their homework. After all, they can sometimes beat us at baseball and outscore us at the bowling alley, too.

In addition to allowing us to have the inner control to study (rather than watching TV) and the cognitive abilities to grasp long division, the frontal lobes are vital to mastering physical abilities, from tennis, to tightrope walking, to getting to the toilet at about age 3.

So, understanding that many regions of the brain work together to program every action and thought, let’s use our slow frontal-lobe timetable as a model to track how children’s physical and cognitive abilities unfold.

Tying It All Together

Question 5.1

In a sentence, explain why language is the core ability that makes human beings special.

Language is what really allows us to penetrate other minds—and our superior mindreading ability is what makes us different from other animals.

Question 5.2

When Steven played hide-and-seek with his 4-year-old nephew, he realized that while Ethan could run very well, the child was having trouble not betraying his hiding place and understanding the rules of the game. The reason is that Ethan’s _________ cortex is on an earlier developmental timetable than his _________ lobes.

Ethan’s motor cortex is on an earlier developmental timetable than his frontal lobes.

Question 5.3

If you learn that a colleague was in an accident and has frontal-lobe damage, what impairments might you expect?

This is a disaster! Your colleague might have trouble with everything from regulating his physical responses, to analyzing problems, to inhibiting his actions.