The Birth of the Mind: How a Tiny Number of Genes Creates the Complexities of Human Thought by Gary Marcus. Basic Books, $26, 278 pages.


The Chapel Hill News


April 4, 2004

The Gift of Gab


By Phillip Manning


Over 400 years ago, René Descartes posited that humans were beings with nonmaterial minds (or souls) inhabiting mechanically operated bodies. Modern scientists don’t see it that way. To them, there is no dichotomy between body and mind. According to the renowned cognitive scientist Steven Pinker, “The mind is what the brain does.” And the brain is a collection of cells, each one organized by DNA just as other cells in our bodies are organized. This premise leads to problems: How can the 30,000 or so genes contained in human DNA create the complexity of the human brain, the tangle of 20 billion interacting neurons that gives us the capacity for language, which distinguishes our species from every other animal and plant?

This is the question that Gary Marcus, a psychology professor at New York University, addresses in his book “The Birth of the Mind.” To answer it, he begins by describing what genes do. Genes are templates for making proteins, big complicated molecules that carry out the myriad tasks of a cell. Some of those proteins are regulatory molecules that tell other genes when to turn on or off. A cell in your liver, for example, contains the same DNA that a brain cell does, but only those genes that make it a proper liver cell are active (or expressed) in making proteins. A cell in your brain, on the other hand, expresses a different set of genes, and that’s what makes it a brain cell.

This regulatory mechanism appears simple, but it can become quite complicated. The expression of one gene, for example, can be a precondition for the expression of another and that one can express or suppress yet another gene. As Marcus says, “most genes act as parts of elaborate networks.” Thus, “a single gene that is at the top of a complex network can indirectly launch a cascade” that causes hundreds or thousands of other genes to be expressed or suppressed.

But environmental signals can also alter gene expression and the brain’s neural connections, and these changes can affect an already developed brain. When a laboratory mouse raised in a drab cage is exposed to surroundings rich with toys and gadgets, it expresses genes that cause its brain to form new neural connections. In effect, the environment interacts with the mouse’s genes to make a smarter mouse. Of course, not every brain connection can be modified; most are fixed. No matter how many toys a mouse has, its DNA will never allow it to communicate as well as a two-year old.

So, what does make the human brain unique? What gives us our ability to transmit information using complex, syntactical language? It’s not brain size alone. Whales and elephants have larger brains, and while they can communicate in elementary fashion with other whales and elephants, they are not in our ballpark in expressing abstract thoughts and emotions. Nor do our abilities with language come from the sheer number of genes in our DNA. A mustard plant has 27,000 genes, only a few thousand shy of our own genome, but this does not enable it to invent calculus or fall in love or write “Moby Dick.”

For 100 years, scientists have attributed our knack for language to two regions in the brain, Broca’s area and Wernicke’s area. However, recent experiments using brain scans indicate that many other areas of the brain are active in processing language. In truth, Marcus writes, “we simply cannot point to a particular spot in the brain and say that this is the language area.”

Similarly, we cannot point to a single gene or group of genes and say, These are what make language. About 98.5 percent of our DNA is identical with that of chimpanzees, but those small changes lead to huge differences in our ability communicate and think compared to our closest relatives. Scientists have begun to home in on what those small changes might be. They have discovered that a disproportionally large amount of the difference between the human and chimpanzee genomes lies in stretches of DNA that produce regulatory proteins, the molecules that govern the expression of other genes. Thus, the source of language may lie not in a “language gene” but in new ways of regulating old genes, many of which we share with chimps and mustard plants.

Just as a relatively small number of genes creates the incredible complexity of the human mind through an elaborate system of gene expression and suppression, the regulatory genes also appear to give rise to language, the supreme human gift. Descartes, once said “I think, therefore I am.” Of course, Descartes knew nothing about regulatory genes and the cascade of effects they can produce. Today, he might say — I am the product of my genes, therefore I think and speak.
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