One of the recent surprises has been the use of particular proteins for two or more entirely different biochemical functions. Crystallins, which are proteins found at high concentrations in the lens of the eye, provide one of the most dramatic examples. Joram Piatigorsky has made a lifetime study of crystallins, in the course of which he discovered that these proteins have dual lives. Many of them are identifical to well-known enzymes, which serve "housekeeping" functions in metabolism throughout the body, but they also perform an additional optical task in the lens, apparently unconnected with their metabolic activities. This is extraordinary; it is as if, while wandering through an unfamiliar house, one came upon a wall made out of telephones instead of bricks. . . .
Moonlighting has significant evolutionary consequences, because a gene encoding a protein with a single function can evolve under natural selection so as to maintain optimality, but a gene encoding a protein with two functions is likely to get pulled in two directions at once.
Genes procide instructions for generating form and pattern de novo, but they do not directly describe the pattern itself. Growth and morphogenesis must involve physiology, and homeostatic mechanisms that ensure stability during growth are operational throughout development. Turner's hero is the great nineteenth-century physiologist Claude Bernard, who emphasized the importance for lie of "la fixite du milieu interieur"; and Turner would like to put agents of homeostasis, referred to as Bernard machines, on an equal footing with agents of variation and natural selection, or Darwin machines. . . .
. . . one can respond by pointing to evolution itself. The genome changes only in tiny amounts, from generation to generation, and that fact along tells us that the effects of physiology are read back into the germline only slowly and indirectly. Within the lifetime of an animal or plant, a great deal happens at a physiological level that does affect gene expression within its millions of somatic cells, often in profound ways, but these changes in gene activity are almost never propagated to the next generation. Darwin, and not Lamarck, is still the king.
Books to read:
Shakespeare's Poems, edited by Katherine Duncan-Jones and H. R. Woudhuysen.
Everything Is Conceivable: How assisted reproduction is changing men, women and the world, Liza Mundy.