Abstract

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.

Highlights

  • Haven’t we heard this before? Didn’t President Clinton announce in 1996 that a Martian meteorite recovered in Antarctica [1] ‘‘speaks of the possibility of life’’ on Mars? (No, it turned out to be mineralic artifacts.) Wasn’t some ‘‘alien’’ arsenicbased life discovered recently in Mono Lake, California [2]?

  • Toxic environment.) Didn’t Craig Venter and his colleagues recently create a synthetic bacterial cell [3], ‘‘the first selfreplicating species we’ve had on the planet whose parent is a computer’’? (No, its parent is Mycoplasma mycoides and its genome was dutifully reconstructed through DNA synthesis and PCR amplification.)

  • Why are we so confused that we have such trouble distinguishing life from non-life and distinguishing our biology from another? A key limitation is that we know of only one life form, causing us to regard life from that singular perspective (Figure 1)

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Summary

Rolling the Dice

Is the probability that a temperate, rocky planet will generate life? Science cannot say. (Box 1) Biological systems are distinguishable from chemical systems because they contain components that have many potential alternative compositions but adopt a particular composition based on the history of the system. When faced with such real or hypothetical situations regarding alternative life, it is useful to frame the question in terms of information: How many heritable bits are involved, and where did they come from? In this sense biological systems have a molecular memory (genotype), which is shaped by experience (selection) and maintained by selfreproduction. The bits accrue as potential alternative compositions are excluded and specific compositions are Citation: Joyce GF (2012) Bit by Bit: The Darwinian Basis of Life.

Giardia Trichomonas
Pathways to Life
Getting Started
Second Life?
GG G
Full Text
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