All known examples of life belong to the same biology, but there is increasing enthusiasm among astronomers, astrobiologists, and synthetic biologists that other forms of life may soon be discovered or synthesized. This enthusiasm should be tempered by the fact that the probability for life to originate is not known. As a guiding principle in parsing potential examples of alternative life, one should ask: How many heritable “bits” of information are involved, and where did they come from? A genetic system that contains more bits than the number that were required to initiate its operation might reasonably be considered a new form of life.
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| Potential pathways to life on Earth, beginning with a habitable planet and ending with DNA/protein-based life. The planet is an artist’s conception of the recently discovered ‘‘Earth-like’’ planet Kepler-22b (image courtesy of NASA/Ames/JPL-Caltech). Prebiotic chemistry is represented by the Miller-Urey spark-discharge apparatus (modification of photo by Ned Shaw, Indiana University). Two examples of hypothesized pre-RNA life are shown, based on either threose nucleic acid (TNA) or glycol nucleic acid (GNA) |
Source:
- Joyce GF (2012) Bit by Bit: The Darwinian Basis of Life. PLoS Biol 10(5): e1001323, May 8, 2012
