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Building the Brain
The Birth of the Mind:
How a Tiny Number of Genes Creates the Complexities of Human Thought

by Gary Marcus

Reviewed by
Edward R. Winstead

Book Reviews


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Book Reviews


When the world learned a few years ago that humans have only twice as many genes as fruit flies, some news reports said the finding was an insult to our species. After all, aren’t humans more than twice as biologically complex as flies?

The point seems to be exactly the opposite: Humans get by with relatively few genes, so we must have picked up some marvelous biological innovations over the course of evolution that help us make the most of what we have.

These biological innovations presumably have their roots in our genome. The connection between genes and the brain is the subject of an interesting and accessible new book, The Birth of the Mind. Author Gary Marcus writes that progress in genomics means that we are now ready to learn about the mind by understanding how genes build the brain.

Scientists need to know a lot more about the roles of individual genes to tell the full story. But Marcus brings together recent research on genes and the brain, and he provides a useful framework for thinking about the organ that does our thinking.

The brain is really no different from other organs in its construction, according to Marcus, a research psychologist at New York University. Like the heart and the liver, the brain is basically a collection of proteins, and its abilities stem from its physical properties—which in turn are the products of genes.

Genes generally do in the brain what they do elsewhere in the body, switching on when they’re needed. In Marcus’s view, nature and nurture are equal partners as the brain is built because a cell’s internal genetic program is influenced by what happens outside the cell.

The brain of a newborn is partially organized, or “prewired,” and ready to learn. It is not, however, “hardwired,” which implies a kind of inflexibility that could prove disastrous if errors occur.

“Nature has been very clever indeed,” Marcus writes, “endowing us with machinery not only so fantastic that it can organize itself but also so supple that it can refine and retune itself every day of our lives.”

The second chapter, called “Born to Learn,” may be of particular interest to new parents. It describes how newborns pick up differences in language and how infants make sense of the world so early in life.

“It’s not all there at birth,” he notes. But “children are born with sophisticated mental mechanisms (nature) that allow them to make the most of the information out there in the world (nurture).”

The book picks up steam once some basic biological principles have been covered and the author turns to questions about what it all means. For example, how did humans develop language? He recounts the story of the discovery a few years ago of the first gene linked to language in humans.

This and other material may be familiar to newspaper readers, but Marcus weaves together stories nicely and his arguments often rely on common sense.

For instance, he makes a welcome plea for people to stop talking about the genome as a blueprint for the body. Instead, he writes, “We have come to understand the genome as a complex, dynamic set of self-regulating recipes that actively modulate every step of life.”

The book is timely. It’s now possible to compare the genomes of people and chimpanzees, our closest genetic relative, and the search is on for the genes that make us human. So far no smoking gun has been found, and there probably isn’t a smoking gun.

But some of our uniquely human abilities may be due to the duplication or modification of a single gene. (There is evidence for this from research on seeing colors.) Our species may have acquired new mental abilities because a modified gene regulates a collection of existing genes in a novel way.

This could help explain why the human and chimpanzee brains function so differently, despite our genetic similarities. It also suggests that our descendents, many generations from now, may have wondrous mental abilities that we cannot imagine today—all because of small changes in the genome.

Marcus, Gary. The Birth of the Mind: How a Tiny Number of Genes Creates the Complexities of Human Thought. Basic Books, New York. 2004.

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