Multiple Clocks in the Evolution of Living Organisms
Looking for a common origin of all things is pervasive. This is reflected in the idea of a common clock ticking in parallel with evolution. Yet, two stages mark any form of life, multiplication and being alive without multiplying. Also, constructing more biomass puts together at least three space dimensions: the cell volume, its membranes and its genome. This creates a massive selection pressure on the linear structure of DNA, which must to be synthesised in parallel with the cell’s volume, tending to increase the length of DNA and to decrease the availability of its building blocks while fitting with the core metabolism of the cell. The increase of genome length favours ingress of horizontally transferred genes. The limitation of deoxyribonucleotide synthesis is ensured by using nucleoside diphosphates, not triphosphate, as precursors. Furthermore this synthesis is metabolically tied up with gene expression and membrane synthesis. Evolution trees are built up according to the evolution of multiplication, forgetting that ageing organisms can still produce a progeny. Taken together these processes imply that there is no common clock ticking at the same rate for all the functions essential for the evolution of life.
This work benefited from discussions held in the E-seminar Stanislas Noria.
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