DNA and proteins need one another, but could not have come about at the same time.
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.
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:
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:
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.)
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Last update: 12 Feb 2015
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