Defender's Guide to Science and Creationism

Mark Vuletic

Assertion

DNA and proteins need one another, but could not have come about at the same time.

Background

The creationist contention is that DNA cannot replicate without the aid of certain proteins, but that those proteins cannot form unless they have been specified by a sequence of DNA. The origin of life therefore would have required DNA and all of the necessary proteins to suddenly appear together at the same time, which is too improbable.

Analysis

The creationist contention is built upon a false assumption. While modern genetic systems may require both nucleic acids and proteins to function, the precursors from which they evolved may not have.

I. Primitive genetics first

One possibility is that modern genetic systems began as more primitive systems built of components (usually nucleic acids) that did not require proteins to function, either because they were self-catalyzing or because the catalysis was mineral-based. The prime example of a genetics-first proposal is the "RNA world" hypothesis (which is based on nucleic acids but not on DNA) according to which

when life emerged, RNA performed two major enzymatic activities. First, it functioned as a replicating enzyme and replicated itself without a protein. Second, at a later stage, RNA started to catalyze the different processes involved in protein synthesis. Gradually, following processes of natural selection, the proteins synthesized in this manner became the efficient enzymes known to us today and could replace the RNA enzymes. Later, the change from RNA to DNA took place. (Fry 2000:136)

A few other proposals that invoke simpler genetic systems include:

  • Albert Eschenmoser's pyranosyl-RNA hypothesis (Eschenmoser 1994).
  • Stanley Miller's urazol-substituted RNA hypothesis (Kolb et al. 1994).
  • Peter E. Nielsen's peptide-nucleic acid (PNA) hypothesis (Nielsen 1993).
  • Graham Cairns-Smith's clay mineral precursor hypothesis (Cairns-Smith 1982 and 1985).

II. Primitive metabolism first

A different set of proposals suggests that free-standing metabolism arose first, not necessarily based on proteins, and with very rudimentary non-nucleic acid hereditary mechanisms. Some current metabolism-first proposals include:

  • Freeman Dyson's "double-origin" hypothesis (Dyson 1985)
  • Stuart Kauffman's autocatalytic theory (Kauffman 1993; see also Chapter 3 of Kauffman 1995)
  • Günter Wächtershäuser's pyrite hypothesis (Wächtershäuser 1992)

None of these hypotheses, or any of the many other hypotheses and variations on hypotheses, has yet gained a consensus, and in fact some of these hypotheses suffer from serious and well-known problems, which may or may not be patched up in the future. But it should be clear that it is simply not possible to stipulate in advance, as the creationists do, that the interdependence of modern proteins and nucleic acids demonstrates that genetic systems could not have come into existence naturally. The question of whether or not a natural origin of life is possible can only be settled by waiting for the researchers to exhaust their hypotheses. (Much of the information for this part was gathered from Chapters 11 and 12 of Fry 2000; interested parties are strongly encouraged to read the book for more details.)

References

Cairns-Smith AG. 1982. Genetic Takeover and the Mineral Origins of Life. Cambridge: Cambridge University Press.

Cairns-Smith AG. 1985. Seven Clues to the Origin of Life. Cambridge: Cambridge University Press.

Dyson F. 1985. Origins of Life. Cambridge: Cambridge University Press.

Eschenmoser A. 1994. Chemistry of potentially prebiological natural products. Origins Life Evol. Biosphere 24:238-240.

Fry I. 2000. The Emergence of Life on Earth: A Historical and Scientific Overview. New Brunswick: Rutgers University Press.

Kauffman SA. 1993. Origins of Order: Self-Organization and Selection in Evolution. New York: Oxford University Press.

Kauffman SA. 1995. At Home in the Universe: The Search for the Laws of Self-Organization and Complexity. New York: Oxford University Press.

Kolb VM, Dworkin JP, and Miller SL. 1994. Urazole is a potential precursor to uracil. Origins Life Evol. Biosphere 24:107-108.

Nielsen PE. 1993. Peptide nucleic acid (PNA): a model structure for the primordial genetic material? Origins Life Evol. Biosphere 23:323-327.

Wächtershäuser G. 1992. Groundwork for an evolutionary biochemistry: the iron-sulfur world. Prog. Biophys. Molec. Biol. 58:85-201.

Last update: 12 Feb 2015

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