Book Review

The Triple Helix: Gene, organism, and environment

N Engl J Med 2000; 343:667August 31, 2000

Article

The Triple Helix: Gene, organism, and environment
By Richard Lewontin. 136 pp., illustrated. Cambridge, Mass., Harvard University Press, 2000. $22.95. ISBN: 0-674-00159-1

The thinking that distinguishes biology from other sciences originated in the 19th century with Darwin's appreciation that members of all species exhibit phenotypic variation. This led to the idea that change in external circumstances would favor some phenotypes over others and that such selection could in time result in the evolution of new species. In the 20th century, biology attracted many chemists and physicists. Rather than observe organisms, they broke them into components, which they then studied in great detail. By necessity, this reductionist approach could be used with only a few species, but that was of little concern, because universality was thought to apply to the important things in life. To many, this point was proved by the discovery of the structure of DNA. Molecular genetics was thus started, a field that in 40 years would commercialize biology and lead to the scramble to sequence the human genome.

Like any large construction project in the public domain, sequencing the human genome has been a subject of discussion and controversy. Major issues have been the cost of the project, its scientific merit, and the effects of the knowledge gained on human affairs. The concern about cost subsided as the project proved viable and attracted private funding. That leaves the other two questions: What will we learn from this sequence, and how will it affect our lives? With fame and fortune to be made in the genome business, one can only be skeptical of the wondrous claims made by the project's protagonists. The Triple Helix examines these questions from a critical and biologically informed angle.

Richard Lewontin, the Alexander Agassiz Research Professor at Harvard University's Museum of Comparative Zoology, attained scientific prominence in the 1960s with his pioneering studies of genetic variation in fruit flies. Both his work and that contemporaneously undertaken by Harry Harris in humans showed that the amount of genetic variation in nature provided plenty of material on which natural selection could operate. This was indeed “the stuff of evolution.” More recently, Lewontin has written an impressive number of books and articles for the nonscientist, with the aim of explaining, criticizing, and deflating the many debatable and often self-serving claims made in the name of genetics. For readers unfamiliar with his perspective on science and scientists, the The Triple Helix is the ideal introduction. This slim and readable book covers much of Lewontin's ground.

For Lewontin and those whose scientific focus is the genetic variation among members of a species, the human genome project has always appeared half-cocked because of its failure to consider seriously the natural variation that distinguishes individuals. To the public at large this should also seem a curious state of affairs, because in every aspect of the world, it is the differences between individuals that loom large, not the similarities. Lewontin also worries about claims that the genome sequence is a blueprint specifying how a human is made and even what it means to be human. With a humanist perspective and salutary lessons in evolutionary and organismic biology, Lewontin counters the increasingly pervasive view that genes are all that is needed to specify an organism.

Genes represent only one of the three strands in Lewontin's triple helix, the others being the organism and the environment. He reasons that organisms are not determined solely by their genes but also by the environment in which they develop and live. This is hardly contentious and is amply supported by evidence drawn from everyday human experience. Height, weight, shape, agility, health, life span, and most other properties of human bodies are all influenced by the environment in which the bodies gestate, grow up, and live. Genetic factors also affect these properties, and for each individual organism, the actual phenotype is the result of the interplay between genes and the environment. Thus, persons of all genotypes will become larger and heavier on a diet of modern fast food than on a diet of traditionally slow fare. In effect, the genome is a set of boundary conditions that limits the nature of the organism, not a blueprint that defines it.

Although ecologic niches are often discussed as though they were static entities, Lewontin asserts that through its behavior each species is always changing its own environment. Such changes in the environment, in turn, cause natural selection to alter the population of organisms living in the environment. Selection acts on the phenotypic variation that exists within the population, favoring the survival of certain phenotypes over others. Thus, for example, a shortage of food will favor the survival of organisms that obtain food most efficiently or that make the best use of whatever food is available. Although natural selection acts on organisms, not genes, it does have the effect of increasing the frequencies of certain gene variants and decreasing the frequencies of others. In this way, Lewontin sees the environment as actively determining the types of genes, as well as organisms, to be found within it. Because of the continual interplay of mutual modification by genes, organisms, and the environment, no species ever becomes fully adapted to its environment.

In Lewontin's triple helix, the genes are placed in their natural context, where history and geography shape the nature of organisms and the genes they contain. His differences with the most modern of molecular and cellular biologists are irreconcilable and reflect the ever-widening gulf between biologists who have an affinity for what goes on outside the laboratory and those for whom the differences between individuals and between species represent “an annoyance [to be] ignored whenever possible.” In many laboratories, organisms are now studied under conditions in which genetic variation is eliminated and the environment held constant. It is only under these special conditions, where neither variation nor natural selection is tolerated, that the triple helix collapses into the double helix and genes appear to be paramount.

Peter Parham, Ph.D.
Stanford University, Stanford, CA 94305