Concerted Evolution

When astrobiologist and Prof. Emeritus, David Deamer, of the University of California, Santa Cruz, discusses "How Did it all Begin?", his lecture starts with a mythical voyage through the cultural references that inevitably shape our view of other worlds. "Movies are the myths of late-20th century western culture. Because of the power of films like ET to capture our imagination, we are more likely than past generations to accept the possibility that life exists elsewhere in our galaxy."

Sounds of Earth
On the chance that someone is out there, NASA approved the placement of a phonograph record on each of the Voyager spacecraft. The recording, called "Sounds of Earth" fits on a 12-inch, copper disc containing greetings from Earth people in 60 languages, samples of music from different cultures and eras, and natural sounds of surf, wind and thunder, and birds, whales and other animals. The record also contains electronic information that an advanced technological civilization could convert into diagrams, pictures and printed words, including a message from President Carter. Credit: NASA

Indeed among cultural references, no single exchange between another galactic civilization and Earth stands out like the musical exchanges that resonated in one of the first such popular films, "Close Encounters of the Third Kind". For its dramatic closing, music became a universal form of complex communication that transcended the otherwise untranslatable language barrier. Music is part of the tentative terrestrial messages for science as well. When a quarter-century ago, the Voyager probes carried outwards the symbols of terrestrial civilization on a golden record, the mixture of choices available to the scientific community at that time included images, music and languages. The languages–more than 55 in all–welcomed any listener to Earth. Spoken greetings ranged from ancient Akkadian to modern Wu. The music ranged from Chuck Berry to Bach. And the images included a mixture of scientific motifs, like DNA, solar systems, and human anatomy.

But the early Voyager efforts predated much of the startling advances in genetics. When Voyager launched in 1977, the DNA helix was known but no complete organism on Earth was even close to being sequenced. Today, that is where David Deamer has applied the current science of DNA to craft a new and surprisingly musical message. His work with musicians has spawned a new genre in music, where DNA sequences are given musical notes, and encoded for both our listening, as well as what might provide a fitting transmission to accompany the DNA helix first sent out on the Voyager record.

Crafting Beethoven’s Fifth in Four Base Pairs

When Prof. Deamer saw the first portion of a repeating sequence of about 300 bases found throughout all the DNA of the human body, he reported seeing it as resembling musical notations: C-T-G-G-G-C-G-T-G-G-T-G-G-C-T-C-A-C-A-C-C-T-G-T-A-A-T-C-C-C. The letters stand for base-pairs or DNA subunits that pair up with their opposing (G-C, T-A) molecules to form the familiar DNA helix. He wrote: "When a colleague showed me this sequence (which had just been discovered in his laboratory), the first thought that came to mind was that it could almost be musical notation. There were the notes of C (cytosine), G (guanine), and A (adenine), which represent three of the four bases found in DNA. If T, the symbol for the fourth base (thymine), were transposed into the note E, we would have four musical notes that fit nicely into the key of C….Could there really be a musical message in our genes?"

Test Tube Cymbals

Professor Deamer’s curiousity is shared by colleagues at the University of Wales. When the Welsh Computer Science Department first published a program to analyze DNA musically, Dr. Ross King noted in the London Times that "proteins are beautiful and similar to music in structure–neither completely repetitive nor completely random".

The question of a genetic musical message is indeed central to an entire evolutionary debate aptly called "Concerted Evolution". Each organism has a DNA structure wrapped into larger blocks or chromosomes, and those chromosomes–23 pairs for humans–have very few superficial similarities. The length differences alone can span 700% from shortest to longest sequences. At first glance, these differences suggest that the chromosomes evolved independently of each other.

But a larger statistical analysis–akin to musical analysis– is only now beginning to reveal remarkable similarities, which in turn suggest that a kind of concerted evolution, or even common ancestral molecules, might have a role to play in how DNA evolved. If one chromosome was duplicated and slightly modified from another, then subsequently evolved in a similar cellular environment, some statistical history should be discernable. The debate itself is only possible with the large number of whole organisms now sequenced in genetic libraries.

Because of the complexity of a single strand of DNA, scientists have long sought new ways to compare and communicate such complex information. Whether among colleagues or the distant neighbors that might read the original Voyager DNA helix, the message is often cryptic. [For instance, if all the DNA in one human cell could be arranged and straightened out as a single strand, it would measure about 1.5 meters long. And comparing the trillions of cells in a single person makes for astronomical dimensions]. So code visualization has reached a stage of statistical sophistication that rivals what even the most well-tuned music critic might disassemble from a long sequence of contrasting notes. But what has become clear from such complex analysis is that not only do chromosomes have a kind of concerted evolution (statistical similarities), but also they have the same similarities that one expects in good music. This kind of correlation is often called a fractal spectrum, meaning that it shares features apparent when viewed across narrow statistical windows as well as broad segments.

What’s Next

For audiophiles who share an interest in astrobiology, there are a number of forthcoming missions and opportunities to listen in. In 2007 the French NetLander mission will feature what is called the Mars Microphone, to transmit back to Earth the sounds from the surface of the Red Planet.

Meanwhile, a quarter-century journey by the Voyager probes continues to carry both greetings in the languages of many terrestrial civilizations, as well as images of DNA. See related musical source links for converted annotations, including mobile phone ringtones for DNA.


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