Berlinski continued: an alphabet in every living creature .... DNA .... acts as life's primordial text, the code itself organized in nucleic triplets, like messages in Morse code. Each triplet is matched to a particular chemical object, an amino acid. ....They correspond to letters in an alphabet. ..... Like the nucleic acids, proteins are alphabetic objects ..... On average, proteins are roughly 250 amino acid residues in length, so a given protein may be imagined as a long biochemical word, one of many. ..... The MIT physicist Murray Eden ..... estimates the number of the viable proteins at 10 to the 50th power. ..... It would seem that evolution, Murray Eden writes in artfully ambiguous language, "was directed toward the incredibly small proportion of useful protein forms. . . ,"
Planets of Possibility
THIS IS not yet an argument, only an expression of intellectual unease; but the unease tends to build as analogies are amplified. The general issue is one of size and space, and the way in which something small may be found amidst something very big.
Linguists in the 1950's, most notably Noam Chomsky and George Miller, asked dramatically how many grammatical English sentences could be constructed with 100 letters. Approximately 10 to the 25th power, they answered. This is a very large number. But a sentence is one thing; a sequence, another. A sentence obeys the laws of English grammar; a sequence is lawless and comprises any concatenation of those 100 letters. If there are roughly (1025) sentences at hand, the number of sequences 100 letters in length is, by way of contrast, 26 to the 100th power. This is an inconceivably greater number. The space of possibilities has blown up, the explosive process being one of combinatorial inflation.
Now, the vast majority of sequences drawn on a finite alphabet fail to make a statement: they consist of letters arranged to no point or purpose. It is the contrast between sentences and sequences that carries the full, critical weight of memory and intuition. Organized as a writhing ball, the sequences resemble a planet-sized object, one as large as pale Pluto. Landing almost anywhere on that planet, linguists see nothing but nonsense. Meaning resides with the grammatical sequences, but they, those sentences, occupy an area no larger than a dime.
How on earth could the sentences be discovered by chance amid such an infernal and hyperborean immensity of gibberish? They cannot be discovered by chance, and, of course, chance plays no role in their discovery. The linguist or the native English-speaker moves around the place or planet with a perfectly secure sense of where he should go, and what he is apt to see.
The eerie and unexpected presence of an alphabet in every living creature might suggest the possibility of a similar argument in biology. It is DNA of course, that acts as life's primordial text, the code itself organized in nucleic triplets, like messages in Morse code. Each triplet is matched to a particular chemical object, an amino acid. There are twenty such acids in all. They correspond to letters in an alphabet. As the code is read somewhere in life's hidden housing, the linear order of the nucleic acids induces a corresponding linear order in the amino acids. The biological finger writes, and what the cell reads is an ordered presentation of such amino acids-a protein.
Like the nucleic acids, proteins are alphabetic objects, composed of discrete constituents. On average, proteins are roughly 250 amino acid residues in length, so a given protein may be imagined as a long biochemical word, one of many.
The aspects of an analogy are now in place. What is needed is a relevant contrast, something comparable to sentences and sequences in language. Of course nothing completely comparable is at hand: there are no sentences in molecular biology. Nonetheless, there is this fact, helpfully recounted by Richard Dawkins: "The actual animals that have ever lived on earth are a tiny subset of the theoretical animals that could exist." It follows that over the course of four billion years, life has expressed itself by means of a particular stock of proteins, a certain set of life-like words.
A COMBINATORIAL COUNT is now possible. The MIT physicist Murray Eden, to whom I owe this argument, estimates the number of the viable proteins at 10 to the 50th power. Within this set is the raw material of everything that has ever lived: the flowering plants and the alien insects and the seagoing turtles and the sad shambling dinosaurs, the great evolutionary successes and the great evolutionary failures as well. These creatures are, quite literally, composed of the proteins that over the course of time have performed some useful function, with "usefulness" now standing for the sense of sentencehood in linguistics.
As in the case of language, what has once lived occupies some corner in the space of a larger array of possibilities, the actual residing in the shadow of the possible. The space of all possible proteins of a fixed length (250 residues, recall) is computed by multiplying 20 by itself 250 times (20 to the 250th power). It is idle to carry out the calculation. The numbers larger by far than seconds in the history of the world since the Big Bang or grains of sand on the shores of every sounding sea. Another planet now looms in the night sky, Pluto-sized or bigger, a conceptual companion to the planet containing every sequence composed by endlessly arranging the 26 English letters into sequences 100 letters in length. This planetary doppelganger is the planet of all possible proteins of fixed length, the planet, in a certain sense, of every conceivable form of carbon-based life.
And there the two planets lie, spinning on their soundless axes. The contrast between sentences and sequences on Pluto reappears on Pluto's double as the contrast between useful protein forms and all the rest; and it reappears in terms of the same dramatic difference in numbers, the enormous (20 to the 250th power) overawing the merely big (10 to the 50th power), the contrast between the two being quite literally between an immense and swollen planet and a dime's worth of area. That dime-sized corner, which on Pluto contains the English sentences, on Pluto's double contains the living creatures; and there the biologist may be seen tramping, the warm puddle of wet life achingly distinct amid the planet's snow and stray proteins. It is here that living creatures, whatever their ultimate fate, breathed and moaned and carried on, life evidently having discovered the small quiet corner of the space of possibilities in which things work.
It would seem that evolution, Murray Eden writes in artfully ambiguous language, "was directed toward the incredibly small proportion of useful protein forms. . . ," the word "directed" conveying, at least to me, the sobering image of a stage-managed search, with evolution bypassing the awful immensity of all that frozen space because in some sense evolution knew where it was going.
And yet, from the perspective of Darwinian theory, it is chance that plays the crucial -- that plays the only role in generating the proteins. Wandering the surface of a planet, evolution wanders blindly, having forgotten where it has been, unsure of where it is going.
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