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

“At the core of this book is a very simple idea, that what is good enough for the body is good enough for the brain, that the mechanisms that build brains are just extensions of those that build the body. Like Crick’s ‘astonishing hypothesis’— the idea that the mind is the product of the brain—the idea that the brain is the product of the genes should be (to modern ears) scarcely surprising, an idea so natural we might wonder how we ever doubted it” (p. 165). As far as I am concerned, the need for The Birth of the Mind: How a Tiny Number of Genes Creates the Complexities of Human Thought, became apparent on July 17, 1993. A paper announcing genetic linkage between male sexual orientation and part of the X chromosome had been published in Science the previous day. It was introduced to the tabloid-reading British population with extraordinary front page headlines, one of the least inaccurate and offensive of which was the following: “Mums pass gay gene to sons, say doctors”. Scientific shorthand from the era of Mendelian molecular genetics has had a profound effect on popular understanding (or otherwise) of the action of genes. Nowhere is this more apparent than in discussion of cognitive and behavioral functions. When we say “the gene for cystic fibrosis,” we do not mean that the role of this gene is to cause cystic fibrosis. Rather, we mean that absence of a functional protein product of this gene causes cystic fibrosis. Perhaps unavoidably, this usage has spilled over into the discussion of the role of genes in behavior, such that genes “for” IQ, sexual orientation, and many other complex features of behavior are part of common parlance. In fact, these traits and many others are clearly influenced by genes but equally clearly are not determined by them. Conversely, our long affair with the concept of “free will” has made us resistant to the idea that behavior and the “mind” (whatever it may be) are somehow free of the biological nature of the organism that, respectively, performs and contains them. If a popular science book about genes, mind, and behavior is to succeed, it must not only address (and sweep away) several fundamental misconceptions but also replace these easy, if erroneous, views with something closer to current knowledge but still comprehensible. Gary Marcus, in his wideranging overview of our current understanding of the role of genes in the development of the brain (and the product of that organ, the mind), succeeds on many levels. Of particular importance to the relationship between genes and mental function or behavior, he succeeds in producing an equally evidence-based, readable, and detailed laying-to-rest of several misconceptions and sterile debates, alongside a detailed picture of how brains are (and are made) just like any other part of the body. First, Marcus lays out the reasons for believing that the brain is made of cells which, although specialized, are really little different from other cells in the body. Second, he takes on the idea that a single behavior can be encoded by a single gene. A careful but lay-accessible account of the nature of DNA and its information shows what genes do and do not do: “If cars were built by genes, there might be genes for synthesizing different kinds of raw material (rubber, fabric, steel), genes for supervising the construction of subassemblies, and genes for indicating locations within the self-assembling car. Mutations to individual genes might cause problems—an error in the recipe for rubber might cause many of the rubber parts to dissolve more quickly than anticipated, or an error in genes for connecting the spark plugs might lead to an ‘embryonic lethal mutation’ in which the car could never leave the factory. There would be no one ‘steering’ gene or ‘propulsion’ gene . . .” (p. 83). The history of various incomplete ideas about genes, culminating in the definition of genes as “autonomous agents” and complete genomes as “autonomous self-replicating agents,” is an excellent introduction to a major intellectual development in biology. Third, he shows clearly how a set of such autonomous agents can produce the complex and subtle variation that characterizes developmental cascades, the critical series of steps by which products or effects of one gene regulate the activity of others, and makes this understandable. He reviews critical experiments showing that neither the function nor the position of individual neurons and the larger assemblies made of them are absolute, but rather that both respond to local cues in determining where to go and what to do and can be altered by altering the genes they express. Finally, he addresses the sterile absolutist debate over nature versus nurture. Although these absolutist views get more space than their value merits, they have a long history of influence, primarily in psychology but also within neuroscience. Much of the debate about the interpretation of neuronal plasticity seems hard to take seriously these days, but this was not always the case. Writing popular science books is a fine balance between the comprehensible and the reprehensible. Much of what makes books on contemporary cosmology or quantum physics readable to me makes them inaccurate in the eyes of specialists. Such writing is particularly challenging when the author must draw together, in ways at once succinct and meaningful, ideas and information from a number of fields, many of them not the author’s own. As a geneticist and molecular biologist, then, I am prepared to forgive Gary Marcus the occasional inaccuracy in favor of praising the many areas where he really does illuminate current understanding in developmental neuroscience.