Defender's Guide to Science and Creationism

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

Mark I. Vuletic

Last updated 21 March 2008

Background

The creationist contention is that DNA cannot replicate without the aid of certain proteins, but these proteins cannot form unless they have been specified by a sequence of DNA. Abiogenesis therefore would have to involve DNA and all of the necessary proteins suddenly appearing together at the same time, which is improbable enough to discount if only natural forces are in operation.

Analysis

The fact that modern genetic systems require both nucleic acids and proteins to function does not mean that a stepwise evolution of such systems is impossible. Proposals for the origin of modern genetic systems typically posit either that a primitive genetic system arose before metabolism, or else that a primitive metabolism arose before genetic systems.

According to the genetics-first class of proposals, modern genetic systems are descendants of simpler genetic systems which are not necessarily based on nucleic acids and do not require proteins to function, either because the genetic components are self-catalyzing or because the catalysis is 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).

According to the metabolism-first class of proposals, free-standing metabolisms, not necessarily based on proteins, with very rudimentary non-nucleic acid hereditary mechanisms arose before acquiring more complex genetic systems. 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.

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