Abstract
The question ‘what is life?’ has long been a source of philosophical debate and in recent years has taken on increasing scientific importance. The most popular approach among both philosophers and scientists for answering this question is to provide a “definition” of life. In this article I explore a variety of different definitional approaches, both traditional and non-traditional, that have been used to “define” life. I argue that all of them are deeply flawed. It is my contention that a scientifically compelling understanding of the nature of life presupposes an empirically adequate scientific theory (vs. definition) of life; as I argue, scientific theories are not the sort of thing that can be encapsulated in definitions. Unfortunately, as I also discuss, scientists are currently in no position to formulate even a tentative version of such a theory. Recent discoveries in biology and biochemistry have revealed that familiar Earth life represents a single example that may not be representative of life. If this is the case, life on Earth today provides an empirically inadequate foundation for theorizing about life considered generally. I sketch a strategy for procuring the needed additional examples of life without the guidance of a definition or theory of life, and close with an application to NASA’s fledgling search for extraterrestrial life.
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References
Ainsworth G. C. (1976) Introduction to the history of mycology. Cambridge University Press, Cambridge
Bedau M. A. (1998) Four puzzles about life. Artificial Life 4: 125–140
Benner S. A. (1994) Expanding the genetic lexicon: Incorporating non-standard amino acids into proteins by ribosome-based synthesis. Trends in Biotechnology 12: 158–163
Benner S. A., Ricardo A., Carrigan M. A. (2004) Is there a common chemical model for life in the universe?. Current Opinion in Chemical Biology 8: 672–689
Boyd R. (1999a) Homeostasis, species, and higher taxa. In: Wilson R. (ed.) Species: New interdisciplinary essays. Cambridge University Press, Cambridge, pp 141–185
Boyd R. (1999b) Kinds, complexity and multiple realization. Philosophical Studies 95: 67–98
Chalmers D. J., Jackson F. (2001) Conceptual analysis and reductive explanation. The Philosophical Review 110: 315–360
Cleland C. E. (2006) Understanding the nature of life: A matter of definition or theory?. In: Seckbach J. (ed.) Life as we know it. Springer, Dordrecht, pp 589–600
Cleland C. E. (2007) Epistemological issues in the study of microbial life: Alternative terran biospheres?. Studies in History and Philosophy of Biological and Biomedical Sciences 38: 847–861
Cleland C. E., Chyba C. F. (2002) Defining ‘life’. Origins of Life and Evolution of the Biosphere 32: 387–393
Cleland C. E., Chyba C. F. (2007) Does ‘life’ have a definition?. In: Sullivan W. T., Baross J. A. (eds) Planets and life. Cambridge University Press, Cambridge, pp 119–131
Cleland C. E., Copley S. D. (2005) The possibility of alternative microbial life on earth. International Journal of Astrobiology 2: 165–173
Davies P. C. W., Lineweaver C. H. (2005) Finding a second sample of life on earth. Astrobiology 5: 154–163
Dupré J. (1993) The disorder of things. Harvard University Press, Cambridge
Jakosky B. M., Westall F., Brack A. (2007) Mars. In: Sullivan W. T., Baross J. A. (eds) Planets and life. Cambridge University Press, Cambridge, pp 357–387
Joyce, G. F. (1995). The RNA world: Life before DNA and protein. In B. Zuckerman & M. Hart (Eds.), Extraterrestrials—where are they? (Vol. II, pp. 139–151). Cambridge: Cambridge University Press.
Keller E. F. (2002) Making sense of life. Harvard University Press, Cambridge, pp 284–294
Klein H. P. (1978) The Viking biological experiments on Mars. Icarus 34: 666–674
Kripke S. (1972) Naming and necessity. Harvard University Press, Cambridge
Kuhn T. (1962) The structure of scientific revolutions. University of Chicago Press, Chicago
Lange M. (1995) Life, ‘artificial life,’ and scientific explanation. Philosophy of Science 63: 225–244
Lavoisier, A. L. (1783). On the nature of water and on experiments which appear to prove that this substance is not strictly speaking an element but that it is susceptible of decomposition and recomposition. Observations sur la Physique, 23, 452–455 (trans. Carmen Giunta. http://webserver.lemoyne.edu/faculty/giunta/laveau.html).
Locke J. (1689) An Essay Concerning Human Understanding. Oxford University Press, Oxford
Mellor C. H. (1977) Natural kinds. British Journal for the Philosophy of Science 28: 299–312
Needham P. (2002) discovery that water is H2O. International Studies in the Philosophy of Science 15: 205–226
Putnam, H. (1975). The meaning of ‘meaning’. In K. Gunderson (Ed.), Language, mind and knowledge: Minnesota studies in the philosophy of science (Vol. VII, pp. 131–193). Minneapolis, MN: Minnesota University Press.
Psillos S. (1999) Scientific realism: How science tracks truth. Routledge, London
Roberts G. (1994) The mirror of alchemy. University of Toronto Press, Toronto
Ruiz-Mirazo K., Pereto A., Moreno J. (2002) A universal definition of life: Autonomy and open-ended evolution. Origins of Life and Evolution of the Biosphere 34: 323–346
Ward P. D., Brownlee D. (2000) Rare Earth. Copernicus, New York
Woese C. R. (2004) The archaeal concept and the world it lives in: A retrospective. Photosynthesis Research 80: 371–372
Zemach E. M. (1976) Putnam’s theory on the reference of substance terms. The Journal of Philosophy LXXIIII: 116–126
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Cleland, C.E. Life without definitions. Synthese 185, 125–144 (2012). https://doi.org/10.1007/s11229-011-9879-7
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DOI: https://doi.org/10.1007/s11229-011-9879-7