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The Evolution of Photosynthesis...again?
Lynn J. Rothschild
Philosophical Transactions: Biological Sciences
Vol. 363, No. 1504, Photosynthetic and Atmospheric Evolution (Aug. 27, 2008), pp. 2787-2801
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/20208687
Page Count: 15
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'Replaying the tape' is an intriguing 'would it happen again?' exercise. With respect to broad evolutionary innovations, such as photosynthesis, the answers are central to our search for life elsewhere. Photosynthesis permits a large planetary biomass on Earth. Specifically, oxygenic photosynthesis has allowed an oxygenated atmosphere and the evolution of large metabolically demanding creatures, including ourselves. There are at least six prerequisites for the evolution of biological carbon fixation: a carbon-based life form; the presence of inorganic carbon; the availability of reductants; the presence of light; a light-harvesting mechanism to convert the light energy into chemical energy; and carboxylating enzymes. All were present on the early Earth. To provide the evolutionary pressure, organic carbon must be a scarce resource in contrast to inorganic carbon. The probability of evolving a carboxylase is approached by creating an inventory of carbon-fixation enzymes and comparing them, leading to the conclusion that carbon fixation in general is basic to life and has arisen multiple times. Certainly, the evolutionary pressure to evolve new pathways for carbon fixation would have been present early in evolution. From knowledge about planetary systems and extraterrestrial chemistry, if organic carbon-based life occurs elsewhere, photosynthesis--although perhaps not oxygenic photosynthesis--would also have evolved.
Philosophical Transactions: Biological Sciences © 2008 Royal Society