Science Reader Question: Fugue in the Key of Adenine

Photo of sheet music

Variations on a theme are a very common form of musical expression. (Photo by FotoshopTofs)

This month, we’ve been addressing some reader questions on the topic of evolution. Having looked at how God’s intentions could be realized via a process that leaves degrees of freedom for creation, and how those intentions could be communicated and realized in a way that is not coercive, I want to elaborate on the source and nature of variation in evolution. This whole conversation started when I brought up research findings that indicated a retroviral sequence plays a role in human embryonic development. If evolution is just one mutation after another, and if the human genome is cobbled together from whatever viral parts or other tidbits are lying around, then aren’t we just pastiches and not original creations?

Talk about mutations long enough, and someone’s bound to bring up Shakespeare. How many mythical monkey-years must be spent banging on typewriters to get Hamlet? Richard Dawkins notably provided an illustration of selection by showing how to get from random nonsense to the immortal words of the bard “Methinks it is like a weasel.” One character at a time is changed until the desired quote emerges. The demonstration shows how selection works, but it reinforces some unhelpful analogies about DNA and mutations. Language metaphors for DNA are so natural we probably can’t get away from them entirely, but we can try other analogies beyond individual letters.

DNA are long chains of four different chemical subunits (called bases): adenine, cytosine, guanine and thymine. It is efficient to abbreviate these as A, C, G and T, writing out DNA sequences as “GATTACA” or what have you. It’s then intuitive to compare each base to a letter and equate genes to words or sentences. But that’s just an artifact of notation and doesn’t really provide functional equivalence. We could just as accurately write that sequence as “Guanine Adenine Thymine Thymine Adenine Cytosine Adenine.” Then we might naturally think of the individual bases as words.

Let’s see how the word analogy helps. With base-as-letter, a mutation turns “METHINKS IT IS LIKE A WEASEL” to “METHINKS UT IS LIKE A WEASEL” or “METHINKS IT IS LILE A WEASEL.” Every change reads like a corruption or mistake; there are no obvious possible improvements. But if subunits are words, then we can mutate “Methinks it is like a weasel” to “Methinks it is like a walrus” or “Methinks it is like a wombat.” These sentences have changed, but they are still grammatically correct and meaningful. Some options may habe shades of connotation with richer subtext or one word might sound more aesthetically pleasing than another, but each variant is still cromulent English. The shades of nuance between them more accurately reflect the biological implications of mutations.

Photo of a walrus

I’m not 100% certain Hamlet (or Shakespeare) would be familiar with the walrus, but it’s more likely him being familiar with wombats. (Photo by PublicDomainImages)

Once we starting thinking about mutations in terms of words instead of letters, it’s also easier to understand the other kinds of possible changes besides single substitutions. Strunk & White (perhaps wary of too many “words, words, words”) encourage simplicity, recommending you avoid “there is no doubt but that” when “no doubt” will do or shortening “owing to the fact that” to just “since.” Similarly, portions of genes can be deleted from one generation to the next and the result needn’t always be disastrous. Likewise, sequences can be inserted, much as we might add a phrase or clause to a sentence. “And it must follow, as the night the day, thou canst not then be false to any man” does not need “as the night the day” to be grammatical; the addition of the metaphor illustrates the point which can be stated without it. In fairness, not all insertions and deletions are functional, but hopefully this gives you some sense that they are possible operations and not automatically problematic.

Another common source of variation is repetition or duplication. Again, repeating letters is rarely meaningful, but words and phrases can be repeated productively. “My kingdom for a horse!” doesn’t convey as much desperation as the full quote. And while Shakespeare might lament the inelegance, we can meaningfully say “Buffalo buffalo” and “Buffalo buffalo buffalo” and “Buffalo buffalo buffalo Buffalo buffalo” and even “Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo.” Similarly, different numbers of repeats in a DNA sequence can provide meaningful information.

Duplication is a different sort of beast. Whole genes, even portions of chromosomes containing multiple genes, can be duplicated in their entirety. One copy can continue to serve its original function, while the other can be changed to do something else. I employ similar techniques in my writing. If I need a biographical statement, for example, I’ll copy an existing one and modify it to fit the new purpose. It’s easier than starting from scratch and doesn’t break what I’ve already done.

Hopefully, these examples help to broaden the picture of what mutations looks like. I find it more helpful picture variation in evolution as editing and revising a manuscript rather than as banging away on a typewriter to find the needles of recognizable English words in the haystack of random gibberish.

Still, editing and revising might not seem worthy of God; we value originality much more highly. Well, at least we do in writing. In other creative endeavors, variations on a theme are perfectly acceptable expressions of creativity. (And even in writing, we may overestimate originality; ask Shakespeare about Amleth.) I recently enjoyed a Pittsburgh Symphony Orchestra performance of Rhapsody on a Theme of Paganini by Rachmaninov. The piece is revered in the piano and orchestra repertoire; its famous 18th variation is particularly sublime. No one holds it against Rachmaninov that his composition is constructed around a melody by another composer; he is lauded for his skill at transformation. This particular performance had an extra wrinkle: soloist Cameron Carpenter performed on a digital pipe organ, not a piano. He and the orchestra were really playing Carpenter’s own arrangement of the piece, allowing Carpenter to contribute his own flourishes, such as voicing that 18th variation as an accordion, to what Rachmaninov and Paganini wrote.

We are left then with the question of provenance. Even if variations on a theme are a valid way to express creativity, is there any dignity trying to make something out of the detritus of an unwanted retroviral infection? I can only think to answer “I hope so”; if God can redeem a virus, then he can redeem a sinner like me. And on this front, there is good news! The stone that the builders rejected has become the cornerstone. The Bible teems with reclamation projects. Notice too how Jesus takes a quote from Psalms and gives it new meaning by putting it in a new context. In a similar fashion, a retrovirus sequence takes on new meaning as soon as it is inserted into another genome. We may still be able to recognize its origin, but it has been grafted in and afforded the same privileges as sequences that had been there the whole time.

Hopefully this brief, incomplete survey of sources of biological variation helps you see mutations as more than just a series of mistakes. As a closing thought, I recommend reading Tolkien’s Ainulindalë in which he describes the creation of Middle Earth as a musical composition. The evil Morgoth tries to infect the song with his own dark melody, which the creator ultimately harmonizes with the rest of the piece. Perhaps that story might illustrate how to reconcile retroviral infection with creation.

The retrovirus example was raised as a concern with respect to man’s creation in God’s image, so next week we’ll look more directly at the imago Dei.

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Andy Walsh

Andy has worn many hats in his life. He knows this is a dreadfully clichéd notion, but since it is also literally true he uses it anyway. Among his current metaphorical hats: husband of one wife, father of two elementary school students, reader of science fiction and science fact, enthusiast of contemporary symphonic music, and chief science officer. Previous metaphorical hats include: comp bio postdoc, molecular biology grad student, InterVarsity chapter president (that one came with a literal hat), music store clerk, house painter, and mosquito trapper. Among his more unique literal hats: British bobby, captain’s hats (of varying levels of authenticity) of several specific vessels, a deerstalker from 221B Baker St, and a railroad engineer’s cap. His monthly Science in Review is drawn from his weekly Science Corner posts — Wednesdays, 8am (Eastern) on the Emerging Scholars Network Blog.

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