What Genes Can't Do (review)

Let's cut to the chase: What genes can't do, according to Lenny Moss, is make anything. There are no genes "for" blue eyes or Huntington's disease or cancer. Genes are not, despite what we read in the papers, the instruction book or even the computer program for life. They are not, in any meaningful sense, the ultimate cause of any biological traits. Taking this point seriously, Moss argues, will require a radical reorganization of biomedical science, with effects ramifying through basic research, clinical care, and even health policy.

It is becoming a common refrain. Several recent books attack the mainstream version of the gene. The critique takes this general form: recent molecular studies are showing that genes and gene action are complex, interdependent, and environmentally conditioned; this idea overturns the long-standing idea that genes are the ultimate cause of traits; therefore, the history of genetics is revealed to be determinist, therefore ideology-driven, and therefore politically conservative.

Moss's book is different. It is not, thankfully, another quasi-Marxist polemic against the ostensibly right-wing ideology riddling basic research. It is a calm, subtle, stimulating book that attempts to come to terms, historically and philosophically, with the theory of the gene and its implications for science. Moss does criticize much of basic biomedical research, but he does so by learning the science and engaging the data. A philosopher, his contribution is to synthesize several bodies of research, integrate them into the historical scientific context, and point out fallacies and logical flaws in the experimental program.

He begins by putting an original spin on the oft-told history of heredity. In the familiar story, the late nineteenth-century argument over preformationism and epigenesis is a stock vignette. The debate goes back nominally to the eighteenth century, when preformationists believed that embryos contained a homunculus—literally, a tiny man; development was merely his growth, a playing-out of the initial conditions. The epigenesists, in contrast, believed that development proceeded along a series of decision points, each mediated by local environmental conditions. In the nineteenth century, new experimental techniques enabled researchers to reframe the debate in terms of specific questions about the cellular cues that trigger development. Does half an embryo grow into half a larva (preformationism), or a half-size larva (epigenesis)?

Most scholars have assumed that the preformationists won. The modern idea of a genetic program, complete at fertilization, that guides development is widely considered an extension of preformationism. Moss, however, locates a sophisticated version of epigenesis in the work of Wilhelm Johannsen, a Danish plant-breeder best known for his distinction between genotype, or genetic constitution, and phenotype—physical appearance. Moss traces the history of epigenetic thinking forward through the twentieth century, presenting the preformation/epigenesis dichotomy as a fundamental distinction in the theory of the gene.

Moss identifies two gene theories, in fact: gene-P, for preformation, and, not quite parallel, gene-D, for development. Genes-P, in his formulation, are the "genes-for"—P could just as well stand for "phenotype." When Thomas Hunt Morgan said he had the gene that made a leg grow where an antenna should, that was a gene-P. When our newspapers claim the discovery of an obesity gene, a schizophrenia gene, or a crime gene, those are genes-P. Genes-D, in contrast, specify minute steps in developmental pathways. These pathways branch and converge and they are sculpted by environments. Ultimately, they yield the structures that compose traits. Getting from a gene-P to a trait is like a train-ride from one station to the next; with a gene-D, it is like traversing a spiderweb.

Moss argues that both versions of the gene are necessary and constructive— but his heart isn't in it. Deep down, he believes that genes-D are the right...