The Tangled Tree: A Radical New History of Life

by David Quammen

It offered the radical proposition that the universality of the code—all creatures using the same three-letter DNA combinations to call in the same amino acids—reflects a dynamic evolutionary process during the early history of life, not a “frozen accident” traceable to happenstance in one small population of universal ancestors, as Francis Crick had suggested. That proposition was supported in the paper by a computer model and a tonic dose of math. The dynamic process involved “non-Darwinian” mechanisms that made innovation sharing between different lineages possible—and not only possible but also so advantageous that a capacity for such sharing became mandatory. Among those “non-Darwinian” mechanisms, they argued, was horizontal gene transfer, at a level even “more rampant and pervasive” than in later times. Horizontally transferred genes could be valuable to the recipient, by this view, even if the donor organism was still using a slightly different code. And the result of such rampant transferal, among other factors, was consensus on a single mode of coding and translation. Hence the universal code, by which a gene from one lineage of creatures can be optimally applied within another lineage. HGT is not just an ancient and widespread phenomenon, according to Vetsigian, Woese, and Goldenfeld; it was one of the preeminent factors in early evolution, shaping life as we know it and the informational system from which all life is built.