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Is a General Theory of Life Possible? Seeking the Nature of Life in the Context of a Single Example

  • Thematic Issue Article: The Meaning of “Theory” in Biology
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Abstract

Is one of the roles of theory in biology answering the question “What is life?” This is true of theory in many other fields of science. So why should not it be the case for biology? Yet efforts to identify unifying concepts and principles of life have been disappointing, leading some (pluralists) to conclude that life is not a natural kind. In this essay I argue that such judgments are premature. Life as we know it on Earth today represents a single example and moreover there is positive evidence that it may be unrepresentative of life considered generally. Furthermore, as I discuss, the prototype for theorizing about life has traditionally been based on multicellular plants and animals. Yet biologists have discovered that the latter represent a rare, exotic, and fairly recent form of Earth life. By far the oldest, toughest, most extensive, and diverse form of life on our planet is unicellular, prokaryotic microbes, and there are reasons to suppose that this is almost certainly true elsewhere in the universe as well. If there are explanatorily and predictively powerful, biologically distinctive principles for life that can be gleaned from our insular example of life it is more likely that they will be found among the microbes. I discuss some provocative ways in which unicellular microbes differ from multicellular eukaryotes and argue that some of them just might provide us with key insights into the nature of life.

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Notes

  1. While there is disagreement among scholars of Aristotle, this interpretation is common.

  2. Darwin’s nineteenth century theory of evolution by natural selection suggested that many dissimilar-looking organisms (e.g., dogs and whales) descend from a common ancestor, and hence raised the possibility that life on Earth could have arisen from a universal common ancestor. Darwin’s reasoning was based on the idea that natural selection operating on heritable variation can gradually change the morphology of organisms in profound ways over long periods of time. The twentieth century discovery of the remarkable molecular and biochemical similarities among morphologically dissimilar organisms provides powerful support for his theory.

  3. In informal discussions, several microbiologists, including Norm Pace, have suggested this as a likely possibility.

  4. They argue that NASA is not playing fair because the Viking team agreed in advance upon a chemical-metabolic definition of life (DiGregorio 1997), and despite the strangeness of some of the ancillary results of the experiment, the definition was (strictly speaking) satisfied: metabolism, defined in terms of the conversion of a 14C nutrient solution to 14CO2 gas, occurred (DiGregorio 1997), and moreover the reaction was killed when the temperature was raised sufficiently high. This highlights the potential difficulties involved in basing the design of life-detection instrument packages for space missions on a definition of life; for more on this, see Cleland (2012) and Cleland and Chyba (2002).

  5. As discussed in Cleland (2007) and Cleland and Copley (2005), only 1 % of familiar microbes, let alone shadow microbes, can be cultivated, and the powerful molecular biology techniques (metagenomic analysis) developed to circumvent this problem are so closely tailored to the biomolecules of familiar life that they could not detect an even modestly different form of microbial life if it existed. For these and other more theoretical reasons (discussed in the cited papers) one cannot rule out the possibility of a heretofore undetected shadow biosphere descended from an alternative origin of life on Earth.

  6. I discuss these issues in much greater detail in my forthcoming book, The Quest for a Universal Theory of Life: Searching for Life as We Don’t Know It (under contract with Cambridge University Press).

  7. The term “microbe” is used loosely to encompass a large and diverse group of tiny organisms that, with a few exceptions, cannot be seen without the aid of a microscope. Most are single-celled prokaryotes (Bacteria and Archaea) and acellular viruses, but there are notable exceptions such as unicellular Eukarya (e.g., foraminifera) and minuscule, multicellular Eukarya (e.g., rotifers). Eukaryotes are distinguished morphologically from prokaryotes by their cell structure; the distinction is based primarily on the presence of a nucleus and other membrane bound subcellular structures (organelles) in the former but not the latter.

  8. Originally classified together as “bacteria” on the basis of their common prokaryotic cell structure, it is now recognized that Archaea and Bacteria (or Eubacteria) differ from each other in fundamental ways: the genetic machinery of Archaea is more similar to that of Eukarya than that of Bacteria and the chemistry of their cell walls differs from both Bacteria and Eukaya. This led to a major overhaul of the top taxonomic classification scheme, with three domains of life (Bacteria, Archaea, and Eukaryota or Eukarya) replacing the older five kingdoms of life.

  9. I am ignoring viruses because their status as living entities is controversial, and many biologists believe they evolved from prokaryotes; viruses cannot metabolize, and they cannot reproduce without parasitizing living cells. It is an interesting question, however, whether the earliest life on Earth was unicellular. Many researchers working on the origin of life are convinced that encapsulation is a precondition for the energetically uphill, abiotic synthesis of critical biopolymers such as peptides and oligonucleotides (as well as monomeric nucleotides and nucleosides) from more basic molecular building blocks.

  10. The historical Darwin was more open-minded about whether other mechanisms might be at work in biological evolution, but the classical account, which is incorporated into the Modern Synthesis, takes natural selection to be the basic mechanism.

References

  • Beatty J (1995) The evolutionary contingency thesis. In: Wolters G, Lennox JG (eds) Concepts, theories, and rationality in the biological sciences. University of Pittsburgh Press, Pittsburgh, pp 45–81

    Google Scholar 

  • Bedau MA (1996) The nature of life. In: Bedau MA (ed) The philosophy of artificial life. Oxford University Press, Oxford, pp 332–357

    Google Scholar 

  • Benner SA (1994) Expanding the genetic lexicon: incorporating non-standard amino acids into proteins by ribosome-based synthesis. Trends Biotechnol 12:158–163

    Article  Google Scholar 

  • Benner SA (2011) Comments on “A Bacterium that can grow by using arsenic instead of phosphorus.” Science 332:1149

    Google Scholar 

  • Benner SA, Hutter D (2002) Phosphates, DNA, and the search for nonterran life: a second generation model for genetic molecules. Bioorg Chem 30:62–80

    Article  Google Scholar 

  • Benner SA, Switzer CY (1999) Chance and necessity in biomolecular chemistry: is life as we know it universal? In: Frauenfelder H, Deisenhofer J, Wolynes PG (eds) Simplicity and complexity in proteins and nucleic acids. Dahlem University Press, Berlin, pp 335–359

    Google Scholar 

  • Benner SA, Devine K, Matveeva L, Powell D (2000) The missing molecules on Mars. Proc Natl Acad Sci USA 97:2425–2430

    Article  Google Scholar 

  • Biemann K, Oro J, Toulmin P, Orgel LE, Nier AO, Anderson DM, Simmonds PG, Flory D, Diaz AV, Rushneck DR, Biller JE, Lafleur AL (1977) The search for organic substances and inorganic volatile compounds on the surface of Mars. J Geophys Res 82:4641–4658

    Article  Google Scholar 

  • Borhani DW (2011) Comments on “A Bacterium that can grow by using arsenic instead of phosphorus.” Science 332:1149

    Article  Google Scholar 

  • Boto L (2009) Horizontal gene transfer in evolution: facts and challenges. Proc Roy Soc Lond B 277:819–827

    Article  Google Scholar 

  • Cleland CE (2007) Epistemological issues in the study of microbial life: alternative terran biospheres? Stud Hist Phil Biol Biomed Sci 38:847–861

    Google Scholar 

  • Cleland CE (2012) Life without definitions. Synthese 185:125–144

    Article  Google Scholar 

  • Cleland CE, Chyba CF (2002) Defining “life.” Orig Life Evol Biosph 32:387–393

    Google Scholar 

  • Cleland CE, Copley SD (2005) The possibility of alternative microbial life on Earth. Int J Astrobiol 4:165–173

    Article  Google Scholar 

  • Dagan T, Artzy-Randrup Y, Martin W (2008) Modular networks and cumulative impact of lateral transfer in prokaryotic genome evolution. PNAS 105:10039–10044

    Article  Google Scholar 

  • Dawkins R (1976) The selfish gene. Oxford University Press, Oxford

    Google Scholar 

  • Dawkins R (1983) Universal Darwinism. In: Bendall DS (ed) Evolution from molecules to man. Cambridge University Press, Cambridge, pp 403–425

    Google Scholar 

  • Delong EF, Pace NR (2001) Environmental diversity of bacteria and archaea. Syst Biol 50:470–480

    Article  Google Scholar 

  • DiGregorio BE (1997) Mars: the living planet. Grog, Berkeley, CA

    Google Scholar 

  • Doolittle WF, Bapteste E (2007) Pattern pluralism and the tree of life hypothesis. Proc Natl Acad Sci USA 104:2043–2049

    Article  Google Scholar 

  • Doolittle WF, Papke RT (2006) Genomics and the bacterial species problem. Genome Biol 7:116 1–7

    Article  Google Scholar 

  • Duhem, P (1954) The aim and structure of physical theory (Wiener, P. P. (trans.)). Princeton: Princeton University Press.

  • Dupré J (1993) The disorder of things. Harvard University Press, Cambridge, MA

    Google Scholar 

  • Emmeche C (1992) Life as an abstract phenomenon: is artificial life possible? In: Varela FJ, Bourgine P (eds) Toward a practice of autonomous systems. Proceedings of the First European Conference on Artificial Life. MIT Press, Cambridge, MA, pp 466–474

    Google Scholar 

  • Fekry M, Tipton P, Gates K (2011) Kinetic consequences of replacing the internucleotide phosphorus atoms in DNA with arsenic. ACS Chem Biol 6:127–130

    Article  Google Scholar 

  • Fitzgerald MC, Chernushevich I, Standing KG, Kent SBH, Whitman CP (1995) Total chemical synthesis and catalytic properties of the enzyme enantiomers L- and D-4-oxalocrotonate tautomerase. J Am Chem Soc 117:11075–11080

    Article  Google Scholar 

  • Fraser C, Alm EJ, Polz MF, Spratt BG, Hanage WP (2009) The bacterial species challenge: making sense of genetic and ecological diversity. Science 323:741–746

    Article  Google Scholar 

  • Gilles D (1993) Philosophy of science in the twentieth century. Oxford University Press, Oxford

    Google Scholar 

  • Glavin D, Schubert M, Botta O, Kminek G, Bada J (2001) Detecting pyrolysis products from bacteria on Mars. Earth Planet Sci Lett 185:611–616

    Article  Google Scholar 

  • Goldenfield N, Woese C (2007) Biology’s next revolution. Nature 445:369

    Article  Google Scholar 

  • Hogan CM (2010) Biodiversity: bacteria. In: Draggan S, Cleveland CJ (eds) Encyclopedia of earth. National Council for Science and the Environment, Washington DC http://www.eoearth.org/article/Bacteria?topic=49480

  • Hotopp JC, Clark ME, Oliveira DCSG, Foster JM, Fischer P, Torres MCM, Giebel JD, Kumar N, Ishmael N, Wang S, Ingram J, Nene RV, Shepard J, Tomkins J, Richards S, Spiro DJ, Ghedin E, Slatko BE, Tettelin H, Werren JH (2007) Widespread lateral gene transfer from intracellular bacteria to multicellular eukaryotes. Science 317:1753–1755

    Article  Google Scholar 

  • Jakosky BM (2007) Mars. In: Woodruff TS, Baross JA (eds) Planets and life. Cambridge University Press, Cambridge, pp 357–384

    Google Scholar 

  • Joyce GF (1994) Foreword. In: Deamer DW, Fleischacker GR (eds) Origins of life: the central concepts. Jones and Bartless, Boston, pp xi–xii

  • Kauffman SA (2000) Investigations. Oxford University Press, Oxford

    Google Scholar 

  • Keeling PJ, Palmer JD (2008) Horizontal gene transfer in eukaryotic evolution. Nat Rev 9:605–618

    Article  Google Scholar 

  • Keller EF (2002) Making sense of life: explaining biological development with models, metaphors, and machines. Harvard University Press, Cambridge, MA

    Google Scholar 

  • Klein HP, Horowitz NH, Biemann K (1992) The search for extant life on Mars. In: Kieffer HH, Jakosky BM (eds) Mars 1221–1233. University of Arizona Press, Tucson, pp 1221–1233

    Google Scholar 

  • Koonin EV, Wolf YI (2009) Is evolution Darwinian or/and Lamarckian? Biol Direct 4:1–42

    Article  Google Scholar 

  • Lavoisier, M [AL] (1783) On the nature of water and experiments which appear to prove that this substance is not strictly speaking an element but that it is susceptible if decomposition and recomposition. Observations sur la Physique 23: 452-455. Translated by Giunta, CJ (2001) Using history to teach scientific method: the role of errors. J Chem Educ 78:623–627

  • Levere TH (2001) Transforming matter: a history of chemistry from alchemy to the buckyball. Johns Hopkins University Press, Baltimore

    Google Scholar 

  • Lipson H, Pollack JB (2000) Automatic design and manufacture of robotic life forms. Nature 406:260–267

    Google Scholar 

  • McDaniel LD, Young E, Delaney J, Ruhnau F, Ritchie K, Paul JH (2010) High frequency of horizontal gene transfer in the oceans. Science 330:50

    Article  Google Scholar 

  • Mitchell SD (2002) Ceteris paribus: an inadequate representation for biological contingency. Erkenntnis 57:329–350

    Article  Google Scholar 

  • Mojzsis SJ, Arrhenius G, McKeegan KD, Harrison TM, Nutman AP, Friend CR (1996) Evidence for life on Earth before 3,800 million years ago. Nature 384:55–59

    Article  Google Scholar 

  • Olendzenski L, Gogarten JP (2009) Evolution of genes and organisms: the tree/web of life in light of horizontal gene transfer. Ann N Y Acad Sci 1178:137–145

    Article  Google Scholar 

  • Oparin A (1957) Origin of life (translated from 1936 edn). Dover, New York

    Google Scholar 

  • Oyama VI, Berdhal BJ (1976) The Viking gas exchange experiment: results from Chryse and utopia surface samples. J Geophys Res 82:4669–4675

    Article  Google Scholar 

  • Pigliucci M (2007) Do we need an extended evolutionary synthesis. Evolution 61:2743–2749

    Article  Google Scholar 

  • Poole AM (2009) Horizontal gene transfer and the earliest stages of the evolution of life. Res Microbiol 160:473–480

    Article  Google Scholar 

  • Ray TS (1992) An approach to the synthesis of life. In: Langdon C, Taylor C, Farmer JD, Rasmussen S (eds) Artificial life II. Addison-Wesley, Redwood City, CA, pp 371–408

    Google Scholar 

  • Rosenberg A (1994) Instrumental biology, or the disunity of science. University of Chicago Press, Chicago

    Google Scholar 

  • Schulze-Makuch D, Irwin LN (2006) The prospect of alien life in exotic forms on other worlds. Naturwissenschaften 93:155–172

    Article  Google Scholar 

  • Shapiro R (2000) A replicator was not involved in the origin of life. IUBMB Life 49:173–176

    Google Scholar 

  • Sober E (1991) Learning from functionalism: prospects for strong artificial life. In: Langdon C, Taylor C, Farmer JD, Rasmussen S (eds) Artificial life II. Addison-Wesley, Redwood City, CA, pp 749–765

    Google Scholar 

  • Sterelny K, Griffiths PE (1999) Sex and death. University of Chicago Press, Chicago

    Google Scholar 

  • Tsapin AI, Goldfeld MG, McDonald GD, Nealson KH, Moskovitz B, Solheid P, Kemner KM, Kelly SD, Orlandini KA (2000) Iron (VI): hypothetical candidate for the Martian oxidant. Icarus 147:68–78

    Article  Google Scholar 

  • Verela F, Maturana H, Uribe G (1974) Autopoiesis: the organization of living systems, its characterization, and a model. BioSystems 5:187–196

    Article  Google Scholar 

  • Ward PD, Brownlee D (2000) Rare earth. Springer, New York

    Google Scholar 

  • Woese CR (1998) The universal ancestor. Proc Natl Acad Sci USA 95:6854–6859

    Article  Google Scholar 

  • Woese CR (2004) The Archaeal concept and the world it lives in: a retrospective. Photosynth Res 80:361–372

    Article  Google Scholar 

  • Wolfe-Simon F, Blum JS, Kulp TR, Gordon GW, Hoeft SE, Pett-Ridge J, Stolz JF, Webb SM, Weber PK, Davies PCW, Anbar AD, Oremland RS (2011) A bacterium that can grow by using arsenic instead of phosphorus. Science 332:1163–1166

    Article  Google Scholar 

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  1. Department of Philosophy, Center for Astrobiology, University of Colorado, Boulder, CO, USA

    Carol E. Cleland

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Correspondence to Carol E. Cleland.

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Cleland, C.E. Is a General Theory of Life Possible? Seeking the Nature of Life in the Context of a Single Example. Biol Theory 7, 368–379 (2013). https://doi.org/10.1007/s13752-012-0045-3

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