Finally, the committee considered more exotic solutions to problems that must be solved to create the emergent properties that we agree characterize life. It considered a hierarchy of “weirdness”:

  • Is the linear dimensionality of biological molecules essential? Or can a monomer collection or two-dimensional molecules support Darwinian evolution?

  • Must a standard liquid of some kind serve as the matrix for life? Can a supercritical fluid serve as well? Can life exist in the gas phase? In solid bodies, including ice?

  • Must the information content of a living system be held in a polymer? If so, must it be a standard biopolymer? Or can the information to support life be placed in a mineral form or in a matrix that is not molecularly related to Darwinian processes?

  • Are Darwinian processes and their inherent struggle to the death essential for living systems? Can altruistic processes that do not require death and extinctions and their associated molecular structures support the development of complex life?

1.6
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3. Cleland, C.E. 2001. Historical science, experimental science, and the scientific method. Geology 29:987-990.

4. Joyce, G.F., Young, R., Chang, S., Clark, B., Deamer, D., DeVincenzi, D., Ferris, J., Irvine, W., Kasting, J., Kerridge, J., Klein, H., Knoll, A., and Walker, J.1994. In Origins of Life: The Central Concepts (D.W. Deamer and G.R. Fleischaker, eds). Jones and Bartlett, Boston, Mass.

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6. See Brown, J.R., 2003, Ancient horizontal gene transfer, Nature Rev. Genetics 4:121-132; Martin, W., Rotte, C., Hoffmeister, M., Theissen, U., Gelius-Dietrich, G., Ahr, S., and Henze, K., 2003, Early cell evolution, eukaryotes, anoxia, sulfide, oxygen, fungi first (?), and a tree of genomes revisited, IUBMB Life 55:193-204; Ochman, H., Lawrence, J.G., and Groisman, E.S., 2000, Lateral gene transfer and the nature of bacterial innovation, Nature 405:299-304; and Woese, C.R., 2002, On the evolution of cells, Proc. Natl. Acad. Sci. U.S.A. 99:8742-8747.

7. Martin, W., Rotte, C., Hoffmeister, M., Theissen, U., Gelius-Dietrich, G., Ahr, S., and Henze, K. 2003. Early cell evolution, eukaryotes, anoxia, sulfide, oxygen, fungi first (?), and a tree of genomes revisited. IUBMB Life 55:193-204.

8. See Grünberg, K., Wawer, C., Tebo, B.M., and Schüler, D., 2001, A large gene cluster encoding several magnetosome proteins is conserved in different species of magnetotactic bacteria, Appl. Environ. Microbiol. 67:4573-4582; Mazel, D., 2006, Integrons: Agents of bacterial evolution, Nature Rev. Microbiol. 4:608-620; and Mussmann, M., Richter, M., Lombardot, T., Meyerdierks, A., Kuever, J., Kube, M., Glöchner, O., and Amann, R., 2005, Clustered genes related to sulfate respiration in uncultured prokaryotes support the theory of their concomitant horizontal transfer, J. Bacteriol. 187:7126-7127.

9. See Rosing, M.T., 1999, 13C-depleted carbon microparticles in >3700-Ma sea-floor sedimentary rocks from West Greenland, Science 283:674-676; Shen, Y., Buick, R., and Canfield, D.E., 2001, Isotopic evidence for microbial sulphate reduction in the early Archaean era, Nature 410:77-81; and Shidlowski, M.A., 1988, A 3800-million-year isotopic record of life from carbon in sedimentary rocks, Nature 333:313-318.

10. Claverie, J.M., 2006, Viruses take center stage in cellular evolution, Genome Biol. 7:110; Forterre, P., 2006, The origin of viruses and their possible roles in major evolutionary transitions, Virus Res. 117:5-16; Forterre, P., 2006, Three RNA cells for ribosomal lineages and three DNA viruses to replicate their genomes: A hypothesis for the origin of cellular domain, Proc. Natl. Acad. Sci. U.S.A. 103:3669-3674; and Koonin, E.V., and Martin, W., 2005, On the origin of genomes and cells within inorganic compartments, Trends Genetics 21:647-654.

11. Benner, S.A., Ricardo, A., and Carrigan, M.A. 2004. Is there a common chemical model for life in the universe? Curr. Opinion Chem. Biol. 8:672-689.

12. Allamandola, L.J., and Hudgins, D.M. 2003. From interstellar polycyclic aromatic hydrocarbons and ice to astrobiology. In Proceedings of the NATO ASI, Solid State Astrochemistry (V. Pirronello and J. Krelowski, eds.). Kluwer, Dordrecht.

13. Adami, C., and Wilke, C.O., 2004, Experiments in digital life, Artificial Life 10:117-122; Rosing, M.T., 1999, 13C-depleted carbon microparticles in >3700-Ma sea-floor sedimentary rocks from West Greenland, Science 283:674-676; Shen, Y., Buick, R., and Canfield, D.E., 2001, Isotopic evidence for microbial sulphate reduction in the early Archaean era, Nature 410:77-81; and Shidlowski, M.A., 1988, A 3800-million-year isotopic record of life from carbon in sedimentary rocks, Nature 333:313-318.

14. Benner, S.A., Ellington, A.D., and Tauer, A. 1989. Modern metabolism as a palimpsest of the RNA world. Proc. Natl. Acad. Sci. U.S.A. 86:7054-7058.

15. Kauffman, S.A. 1995. At Home in the Universe: The Search for Laws of Self-organization and Complexity. Oxford University Press, New York.



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