Forty2: The first part of your assertion is rather more difficult to attack, so I’m doing it second.
Your claim deals with the probability of an unspecified ‘protein’ forming and folding randomly. I concede that it is extremely unlikely for a protein to form and correctly fold randomly. However, I argue that this does not preclude an abiogenetic origin of life on Earth. I dealt with protein folding in a previous post; now I’ll argue that protein synthesis is also non-random.
Unlike protein folding, proteins do not self-synthesize. You can’t just mix together amino acids and expect to get proteins. Protein synthesis is a directed process; protein sequences are stored in (present-day) cells as DNA, transcribed to messenger RNA by other proteins, and taken to ribosomes, where they pair with complementary transfer-RNAs which add a particular amino acid to a growing ‘proto-protein’. This, incidentally, is called the Central Dogma of Molecular Biology, and is rare among dogmas as being testable and observable (though more has been added to it since its first formulation).
It’s possible to create random proteins: you can add a ‘coupling agent’ to the aforementioned mixture of amino acids, and random amino acid chains (peptides) begin to form. The probability of a given polypeptide forming in this way is (1/20)^n, where n is the number of amino acids in the sequence. For n=100, this is 8 x 10^-131 – it would take many times the age of the universe for a given sequence to appear.
Clearly, proteins do not arise randomly. So we have two possible conclusions:
- Life cannot have arisen without supernatural intervention.
- A mechanism for directed protein synthesis, and perhaps for assembling those proteins that could not self-assemble, existed prior to the first proteins.
The discovery of catalytic RNAs in the early 80s led to the suggestion of an ‘RNA world’, a time when life was based on the catalytic activity of RNA, rather than proteins. While RNA catalysis is rather more limited than that of proteins, it is sufficient to direct protein synthesis – even now, the ribosomes where proteins are synthesized are made up mostly of RNA.
Some, but not all, of these ‘ingredients’ in RNA have been shown to arise from simple chemicals that would have been present in the early atmosphere and oceans. Those which have not yet been observed probably someday will be. Presumably, a mechanism existed for the synthesis of the bases and sugars in RNA and for the assembly of ribonucleotides, the ‘building blocks’ of RNA.
Present-day RNA contains four different bases, but primordial RNA may have had a different (almost certainly smaller) number.
Lacking any knowledge of a non-random process for RNA synthesis that may have existed in the primordial world, I’m going to assume that RNA synthesis, at least at first, is random.
The first step is finding an RNA capable of synthesizing RNA according to a template – a replicator. As soon as such an RNA arose – it would have been a small, crude molecule at first – the possibility for evolution on a molecular level begins. Replicators capable of working more quickly would emerge by slight errors in the replication process, and those new replicators would eventually lead to new replicators, making the old ones obsolete. These replicators would have had the ability to use templates other than their own complements, and they would have made copies of many other RNAs.
It is known that amino acids can arise from simple molecules (e.g. in the Miller-Urey experiment – the conditions of the experiment were not the same as the early atmosphere, but other routes would have existed). And once ribozymes capable of RNA synthesis arose, it would be a matter of time before RNAs began to conduct peptide synthesis. This would probably have been an adaptation of the existing process – they would have used a template, and not merely catalyzed random peptide synthesis.
Essentially, what I’m arguing is that neither protein synthesis nor protein folding is a random process. The sequences of proteins in present-day organisms are the result of billions of years of evolution, and are much more complex than the proteins that would have existed at the beginning of that process.*
*: We know more than you’d expect about the earliest forms of life. By analyzing the DNA of organisms from bacteria to mammals, one can predict what proteins are found in all life, and thus must have been present in the ‘last common ancestor’ of all living organisms.
I think that’s enough for now. Forty2, I’m sure you’re unconvinced. But if there’s anyone here who might be only somewhat doubtful about evolution, maybe I’ve convinced them that it really doesn’t matter what the odds of synthesizing and folding your unnamed protein randomly are. No living thing has ever depended on a randomly-created protein for its existence – organisms carry the information, the result of the lengthy process of evolution, needed to make proteins of their own.**
**: This isn’t true of ribozymes. A process called SELEX (the E stands for evolution…) has been developed for selecting RNA sequences capable of catalyzing a given reaction out of countless random sequences.
There’s a very good website explaining one theory of the origin of life at The Geochemical Origins of Life. There’s a ‘layman’s abstract’ available, but you’ll need a basic understanding of chemistry.