Sunday, July 11, 2010

The similarity between New Testament textual analysis and bacterial plasmid phylogeny

In Prof. Bart Ehrman's excellent lecture series from the Teaching Company called "From Jesus to Constantine" he spends some time explaining the history of the documents of the New Testament. He describes various motifs of textual mutation caused by scribes' errors and theological corrections.

I was struck by the similarity between these motifs and the same motifs in biological DNA mutation.

The most obvious are the point mutations. There are many tens of thousands of spelling differences among the Greek and Latin manuscripts. The vast majority of these are irrelevant as they do not change the interpretation of the text. In biological terms, we might call these "point mutations of synonymous coding regions" which is a really fancy way of saying "spelling mistakes" that do not change the interpretation -- the functionality -- of the DNA. Prof. Ehrman points out that, including these textual point mutations, there are more differences in the Greek manuscripts of the New Testament than there are words!

The second motif is selection. As theological beliefs wandered throughout the centuries, the scribes forced "corrections" on the text to make it more in line with contemporary thought. One example he mentions is the story in Luke of Jesus and his family visiting Jerusalem. In the story the family accidentally leaves Jesus behind. 3 days later (!) they realize they forgot him and go back to find him in the Temple. In the Greek manuscripts Mary says: "You're father and I have been looking all over for you." But at the time the manuscript was being copied many centuries later, the theological orthodoxy had incorporated the story of the virgin birth so how could this passage be right: "your father and I have been looking..." so it was changed to "we've been looking...". This adaption was more "theological fit" than its cousins and was thus selected for in manuscripts over the ages.

The third -- and most incredible -- is the similarity between bacterial plasmids and marginal insertion mutations. The copied manuscripts were used by teachers and would sometimes end up with marginal notes -- writings in a different hand scribbled in the margins of the book. One example of this is the line in first Corinthians chapter 14:34 that "women should remain silent in the churches". Sometimes a scribe would read these marginal notes and think: "that's a good bit, I will maintain it into the next copy." What begins in separate hand becomes a marginal note now written with the same hand as the main-line text. Another generation or more later another scribe comes along and sees this marginal note and thinks: "What's this doing in the margins?" and inserts it into the main line text.

Similarly, in bacteria and other organisms, there's sometimes extra loops of DNA that are independent of the main-line chromosome called "plasmids". These stand-alone pieces of DNA are copied independently of the main-line but are occasionally inserted into the main-line. Once inserted, like the inserted marginal text, they cannot be distinguished from the original thus they become a permanent part of the main-line code. Because we have the sequences of thousands of bacteria, we can see evidence of this throughout history.


flash and zak said...

Whoa, that's awesome!

Anonymous said...

To what extent are each guided by selection for a fitness function? I wonder if there is a way to express the rate and frequency at which fitness criteria change. The modern day has both calcified and put extreme pressure on these texts to change (eg the fitness function WOULD be radically different, yet artificial constraints [printing] inhibit change). Will human ability to manage DNA change do the same for genes?

Adam Norwood said...

Interesting comparison! This reminds me of the recent news that a line from Joyce's "Portrait of the Artist as a Young Man" was included as a watermark in Ventner's synthetic cell genome, and is assumedly deteriorating through successive generations.

PS: I also wanted to say that I've enjoyed your series on math -- it's good to get a different angle on some of these basics that I only half-remember from school, and the etymology lessons are up my alley, too.