Hi Platypus,
I agree with the thrust of your argument.
Words in natural language generally have an arbitrary relationship to the thing that they signify. So we have "dog" in English, but "hond" in German, "chien" in French, etc. It doesn't matter what word we use, as long as the community agrees what each word-sound signifies. In human language, what guarantees the relationship between signifier and signified is a consensus over correct word use. At the level of the sentence, meaning is generated by consensual rules of grammar.
In the case of DNA, on the other hand, the "meaning" of a triplet of nucleotides is a physical property of the structure of transfer RNA molecules. The DNA triplet "CTT" codes for the amino acid leucine because the transfer RNA molecule which bears leucine has the nucleotide triplet "GAA" in its anticodon region, and the connection between the signifier and signified is guaranteed by the physical existence of hydrogen bonds between complementary bases. In natural language, the connection between signifier and signified is not guaranteed by a physical property of the universe in this way.
What difference does grammar make? In human language, the sentence "I like taking my dog for a walk" is well-formed and meaningful, while the 'mutated' version, "I like taking my dog for a", is badly-formed and meaningless, because the interrelationships between component words do not follow consensual rules of grammar.
In DNA, on the other hand, there are no grammar rules, so "ACTGAGACC" is just as meaningful as "ACTGAG". This difference is rooted in the fact that sentences in language are
statements about the world. The sentence "I like taking my dog for a walk" is a statement about the world. The question "where are the bananas?" is a statement to the effect "I want you to tell me where the bananas are". The DNA sequence "ACTGAGACC", in contrast, is not a statement about anything.
Structural constraints on the information content of DNA sequences (for example, the rule that each codon must consist of three nucleotides) should not be confused with grammar because these constraints are not related to the meaning of the DNA sequence. This is clear if you imagine a language consisting only of three-letter words, such that each word is an analogy for a codon. This makes no difference to the grammatical rules of language: "the dog ate ham" is a meaningful sentence while "the ate ham dog" is meaningless. In DNA on the other hand, we can switch around codons as much as we like without ever breaking a grammatical rule and hence generating an "invalid" nucleotide sequence.
The analogy does not work even for stop codons, which might be taken at first glance as corresponding to full stops. If we introduce a full stop into the sentence "the dog ate ham", we might get something like "the." which does not mean anything. If we introduce a stop codon into a DNA sequence we will get a shorter but always grammatically valid protein.
So, for me, it is the question of grammar that is the key difference between DNA and human language. Meaning in human language is mediated by grammar and consensus, while in DNA it is guaranteed by the physical structure of the molecules involved. Meaning can be lost in natural language when sentences are poorly formed. DNA sequences cannot be poorly formed because there is no grammar to define what is "poor".
I suppose that a creationist would say that a DNA sequence corresponding to a nonfunctional protein (or a protein with reduced function) is defined as "poor" based on its effect in the living organism. But to preempt this argument i would point out that poor performance of a protein does not equate to "loss of information", any more than the sentence "I want you to tell me where the bananas are" contains less information when it is ineffective and nobody tells you where to get the fruit.
Mick
Edited by mick, : added last paragraph
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