Massimo Pigliucci on the demise of the genetic blueprint metaphor

Massimo Pigliucci of Rationally Speaking has a short post up on the many problems with “the idea that the DNA sequence of an organism’s genome is analogous to a computer ‘program,’ and that it provides the ‘blueprint’ for building said organism.”

He then goes on to list the many ways in which this idea of ‘mapping’ from gene to body fails to describe the actual process of biological development - which is much more dispersed and complicated than this simple, deterministic figure would suggest.

Pigliucci’s main example, however, can’t help but make use of a new metaphor - the ‘gene network’ - which, it seems to me, brings a new set of problems to bear on the question of metaphor and genetics.

“Ironically, the harbinger of the demise of the genetic program-blueprint metaphor is the serious study of genomics itself. A recent article by Tanguy Chouard in Nature (20 November 2008) explains why. Researchers are finding out that what matters is not so much individual genes, but the way networks of genes function together. Take the example of the Bicoid gene in Drosophila: it was thought to be essential in establishing the form of the body in all insects, based on its effects on the development of body shape in fruit flies. No such thing, as it turns out. Once scientists looked for Bicoid-like genes in other insects they simply did not find them! Turns out that Drosophila is an exception (ah, the perils of “model” organisms), and that in species from wasps to beetles the job carried out by Bicoid is achieved by minor rearrangements of a large regulatory network encompassing a myriad of other genes.“

The term network, and certainly the phrase regulatory network, still imply a computational model, if one that is less ‘causal’ and more ‘conditional’. There is also a lingering governmental association attached to the latter phrase, as if a gene network is itself a self-regulating, separate entity that modulates the body over which it presides. The term network indeed appears in nearly every area of scientific inquiry, and with wildly different meanings.

A recent Science News article, for instance, claimed, somewhat metaphorically, that the “the brain itself is a machine, a network of cells that computes its choices based on the sum of sensory inputs and their interactions with neural anatomy”. Much more could be said for the term network, but suffice it to say, it’s less than baggage-free and in no way promises a circumvention of ‘metaphor’.