When Biology Transformed from Chemistry to Information Theory - Evolution News & Views

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When Biology Transformed from Chemistry to Information Theory

Oswald Avery.jpg

Watson and Crick generally get most of the credit for revealing the information carried by DNA, but as in most scientific advances, they were riding waves of progress behind them. The 1940s were heady days for genetics. In February 1944 (70 years ago this month), Oswald Avery (pictured above), Colin MacLeod and Maclyn McCarty identified DNA as the carrier of a bacterial gene. This began a sequence of major discoveries that concluded in 1970 with uniform agreement that all organisms -- from bacteria to man -- inherit their traits from information coded in DNA molecules. This important period is described by Matthew Cobb in Current Biology, "Oswald Avery, DNA, and the transformation of biology." It's a lively read, picturing competitors at the frontier of a scientific revolution racing to understand what they all know had profound implications.

Cobb's focus is primarily on Avery -- and rightly so, since most in the field recognized the paradigm shift it represented if his findings were true. Many read the Avery paper with interest, calling it "remarkable," "exciting," and "revolutionary." Having expected proteins, with their unlimited variety, to be carriers of genes, they had not been paying as much attention to DNA. Yet despite the celebrations, doubts persisted, leading competitors to continue experiments on proteins. While Avery had shown that a bacterium could adopt the form of another strain, even if it was dead, he had not identified the "transforming principle" that made it possible. Merely switching attention from one chemical to another could not explain the diversity of life.

Cobb appears eager to credit Avery with "the transformation of biology," wanting to set the historical record straight about a largely forgotten figure who preceded Watson and Crick. But a couple of others seem to have recognized the most interesting implications of the Avery paper -- implications that were to switch the focus from chemistry to information. Those two were Erwin Chargaff and Masson Gulland. Watch for their critical insight as we enter a meeting in progress at Cold Spring Harbor Laboratory in 1947:

.... The chemist Erwin Chargaff turned the tables on Mirsky, pugnaciously pointing out that there was no evidence that the nucleoproteins Mirsky had spent his life studying were actually present in cells; it was quite possible that an extraneous protein had bound to the DNA while the two substances were being isolated. Chargaff went on to outline a research programme that would preoccupy many scientists over the coming decade: "If, as we may take for granted on the basis of the very convincing work of Avery and his associates, certain bacterial nucleic acids of the desoxypentose type are endowed with a specific biological activity, a quest for the chemical or physical causes of these specificities appears appropriate, though it may remain completely speculative for the time being. (...) Differences in the proportions or the sequence of the several nucleotides forming the nucleic acid chain also could be responsible for specific effects" [26].

Chargaff's final suggestion touched on the second obstacle to the immediate acceptance of the Avery group's findings: given that DNA was essentially composed of four 'bases' it was unclear how it could produce the almost infinitely different effects produced by genes. It had been thought that the four bases were repeated in a constant, boring sequence, but in 1946 this had been challenged by the British chemist Masson Gulland, who wrote: "there is at present no indisputable evidence that any polynucleotide is composed largely, if at all, of uniform, structural tetranucleotides". Chargaff developed sophisticated techniques for measuring the exact proportion of the different bases and discovered that they were present in different proportions in different species -- DNA was not 'boring', and both he and Gulland suggested that DNA molecules might differ in the sequence of bases. Gulland was tragically killed in a train accident in 1947; had he lived, the history of the study of DNA might have been very different.

Right -- it's not the molecules, it's the sequence! While Cobb goes on to finish the story about Avery, we can see the birth of a key concept in intelligent design was coming to light seven years before Watson and Crick: specified complexity in a coded sequence.

Stephen Meyer also discussed this period in Signature in the Cell. He also sees Chargaff getting the critical insight:

When Erwin Chargaff, of Columbia University, read Avery's paper, he immediately sensed its importance. He saw "in dark contours the beginning of a grammar of biology," he recounted. "Avery gave us the first text of a new language or rather he showed us where to look for it. I resolved to search for this text."

.... More important, Chargaff recognized that even for nucleic acids with the same proportion of the four bases (A, T, C, and G), "enormous" numbers of variations in sequence were possible. As he put it, different DNA molecules or parts of DNA molecules might "differ from each other ... in the sequence, [though] not the proportion, of their constituents." (page 68).

It seems unfair that Watson and Crick, less educated about DNA than Chargaff was, get most of the honor for recognizing DNA as a bearer of information. That's another story. But Chargaff, Gulland, Avery, and all the researchers of that period enjoyed the gradually brightening light of a scientific revolution. Meyer describes some of the luminaries who transformed biology from chemistry to information theory:

Since scientists began to think seriously about what would be required to explain the phenomenon of heredity, they have recognized the need for some feature or substance in living organisms possessing precisely these two properties together. Thus Erwin Schrodinger envisioned an "aperiodic crystal"; Erwin Chargaff perceived DNA's capacity for "complex sequencing"; James Watson and Francis Crick equated complex sequences with "information," which Crick in turn equated with "specificity"; Jacques Monod equated irregular specificity in proteins with the need for "a code"; and Leslie Orgel characterized life as a "specified complexity." (Ibid. p. 387)

Once scientists switched their attention from chemistry to information, the effects were huge. It becomes apparent that life takes on a whole new character that rides on -- but is not derived from -- the material properties of chemicals. The information in DNA can, for instance, be expressed on a computer screen, in a book, or in human thoughts. To manifest itself in action, it uses DNA to direct the operation of the cell, but the information per se is immaterial. Information becomes a fundamental property of the universe, accompanying space, time, and matter.

Looking back over the past seven decades, we can see how this transformation fed the intelligent design revolution. Once the realization was there -- life is informational in nature -- the ID movement has since explored the implications further. While neo-Darwinists, heirs of the old 1930s paradigm, are stuck looking for unguided processes like mutation, ID advocates ask, Where does information come from? From uniform experience, we know of only one source: the activity of a mind or, more generally, intelligent causes.

That's why it is so apt to compare the DNA code to software (another scientific revolution that shortly followed the genetic revolution and has since overlapped with it). We know that software does not emerge from the medium that carries it, whether paper, a computer screen or a whiteboard. It is the product of mental activity. And since humans can even create software with DNA, it seems a secure "inference to the best explanation" that the DNA code had an intelligent cause for its origin. The inference is strengthened by the knowledge that no unguided process has ever produced specified complexity that yields functional information. Signature in the Cell is "the book" making this argument watertight.

So as we pause to remember Oswald Avery and his colleagues for identifying genes with DNA, let us not forget the other pioneers who first glimpsed biology's design revolution.

Image: Oswald Avery/Wikipedia.


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