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. 2010 Dec;10(10):1021-30.
doi: 10.1089/ast.2010.0524.

Defining life

Steven A Benner  1
Affiliations

Defining life

Steven A Benner. Astrobiology. 2010 Dec.

Abstract

Any definition is intricately connected to a theory that gives it meaning. Accordingly, this article discusses various definitions of life held in the astrobiology community by considering their connected "theories of life." These include certain "list" definitions and a popular definition that holds that life is a "self-sustaining chemical system capable of Darwinian evolution." We then act as "anthropologists," studying what scientists do to determine which definition-theories of life they constructively hold as they design missions to seek non-terran life. We also look at how constructive beliefs about biosignatures change as observational data accumulate. And we consider how a definition centered on Darwinian evolution might itself be forced to change as supra-Darwinian species emerge, including in our descendents, and consider the chances of our encountering supra-Darwinian species in our exploration of the Cosmos. Last, we ask what chemical structures might support Darwinian evolution universally; these structures might be universal biosignatures.

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Figures

FIG. 1.
FIG. 1.
Directly studying as “anthropologists of science” what scientists do allows us to understand what scientists constructively believe. By permission from Benner (2009). Color images available online at www.liebertonline.com/ast.
FIG. 2.
FIG. 2.
A scaled comparison of the structure of the ribosome with the structures observed in the Allan Hills meteorite from Mars suggested that the structures were too small to be life. This suggestion assumed that any martian life must make proteins by using terran-sized ribosomes. Color images available online at www.liebertonline.com/ast.
FIG. 3.
FIG. 3.
The repeating charge in the backbones of nucleic acids is hypothesized to be key to allowing DNA and RNA to support Darwinian evolution. It helps force strand-strand interactions as far from the backbone as possible (the origin of Watson-Crick pairing rules). Further, the repeating charge so dominates the biophysical properties of the molecular system that changing a nucleobase (a mutation) does not have any significant impact on the behavior of the molecule, a feature essential to allow the system to evolve. Color images available online at www.liebertonline.com/ast.
See this image and copyright information in PMC

References

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    1. Benner S.A. The Life, the Universe and the Scientific Method. FfAME Press; Gainesville, FL: 2009.
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