The Blank Slate

Pinker states that we are moving towards the idea of a “universal complex human nature” (73). However, there are several modern ideas attempting to undermine this development (74). One is the Human Genome Project, an international effort to study human genetic material. Completed in 2003, the HGP found that there are about 34,000 separate human genes, much less than predicted. Next, the field of connectionism argues that the brain is “like the artificial neural networks simulated on computers to learn statistical patterns” (78). Finally, the idea of neural plasticity, which suggests that the brain is malleable (in other words, the brain may not be a blank slate, but it can be shaped).

Pinker states that neuroscientists who endorse these ideas have selectively interpreted evidence to fit with their pre-established idea of the Blank Slate. First, he takes on the Human Genome Project. Craig Venter, the head of the company that completed the project, said that given the apparently small number of genes found “our environments are critical” (76) in determining our development. However, Pinker counters that “no one knows what these numbers mean” (76). Many biologists, he writes, have said that we are not necessarily less complex than we had thought but that “the number of genes in a genome has little to do with the complexity of the organism” (77). More complex organisms can arise from the same number of genes as less complex organisms.

Pinker contends that connectionism is another way in which the theory of the Blank Slate emerges in modern thinking. Connectionists believe that intelligence is the result of “highly trained but otherwise generic neural networks” (79). Instead, Pinker believes that simple connectionist networks can generalize from one situation to the next and therefore show evidence of learning, but it is not possible to know if they can replicate the complexity of actual human intelligence. Pinker examines the kinds of logical relationships that underlie human reasoning but that cannot be duplicated by a computer’s generic networks. These kinds of relationships include distinguishing between a category and an individual; compositionality (the ability to have a new thought that is not just the sum of other thoughts); quantification (the binding of variables); recursion (the ability to put one thought within another); and categorical reasoning. He also determines that neural networks cannot produce categorical reasoning in language, such as coming up with the past tense of an unfamiliar verb. In other words, because a generic computer network cannot handle the complexities of human thought, intelligence must be the result of something deeper.

The author then discusses neural plasticity. For a long time, neuroscientists could not find the effects of a lifetime of experience on the brain (though people’s experiences surely left impressions on their bodies), but they are now involved in the fashionable field of neural plasticity, or how the brain changes. People can re-dedicate brain tissue to new tasks (for example, blind people use their visual cortex to read Braille). However, Pinker refutes the idea that the brain is largely plastic. It is, after all, not a new idea that learning can affect the brain. Neuroscientists who support plasticity focus on the primary sensory cortex, which is used to process signals in the first phase of sensory analysis, but Pinker produces a diagram that shows that the primary sensory cortex is only one part of a complex system. In addition, he shows that subcortical areas of the brain such as the hippocampus and amygdala are far less plastic (88).

Pinker notes that the brain does not rely simply on a genetic blueprint; it must respond to feedback loops as it develops. However, this does not mean that the environment can shape the brain. For example, the visual system develops in the womb in the dark, without the eyes seeing or sending back any feedback to the brain. Though many systems such as vision and touch follow the idea of “fire-together-wire-together” (93), (meaning that if they work together, they are likely connected by the brain), other systems (such as the olfactory system) do not follow this pattern. It turns out that plasticity is not a good metaphor, Pinker writes, for describing the way a lot of the brain works. For example, Pinker writes about sexual orientation. Some conservative groups attempt to use conversion therapy to turn gay men straight, for example, but it doesn’t work. The mind is not plastic in this regard.

In examining what actually happens during plasticity, Pinker says that most cases involve re-mappings in the primary sensory cortex. For example, the brain area governing the movement of an amputated finger is taken over by the next finger, and deaf people use their language-centered cortical areas to understand sign language. Pinker writes, “Patterns in the input can tune a patch of sensory cortex to mesh with that input, but only within the limits of the wiring already present” (96). Changes do not, in other words, involve totally unrelated parts of the brain.

The observation of baby animals who can use their senses and motor functions immediately after birth shows that genes shape their brains before they are born. Even before the formation of the cortex, neurons form themselves into a kind of “proto-map” in which neurons with different properties are grouped together. This shows that the brain can develop without environmental input. Studies with mice that have a specific gene knocked out show that genes are more important to brain development than neural activity.

This applies to humans as well. For example, some children grow up to be normal after having an entire hemisphere removed from their brain, but that is because they have the other hemisphere to compensate. On the other hand, children who lose the same part of the brain in both hemispheres do not generate the ability to do what their missing part controls.

Therefore, Pinker writes that these defenses of the Blank Slate—the size of the human genome, connectionism, and plasticity—are inadequate. While the brain is not totally impervious to environmental input, there is some innate mechanism in the brain that informs behavior. Studies have shown that different animals vary from each other in their drives and abilities. Human babies are born already having developed complex ways to interpret experience. Many cognitive processes such as language and personality have been shown to be highly genetic, and a person’s temperament has been shown to be fairly constant over time. Therefore, the brain’s architecture comes together via the control of genes.