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Dream a Little Dream of AEG


Did AEG come before DNA? Did a ghost just fly past the window? Did aliens invade my dreams? If you think science should stick to hard facts, you don't know the world of "origin of life" science, where imagination rules.

Astrobiology, a science without a subject, is a hybrid between real-world science and science fiction. Much of it deals with the observable chemistry of life on earth and the geochemical conditions of other worlds. That's all good science: it's observable in the here and now. But to think today's chemistry has anything to do with the origin of life requires an existential leap into an unobservable past. The best an astrobiologist can do is "suggest" that a certain scenario is possible.

The power of suggestion rules astrobiology. Look at this headline from NASA's Astrobiology Magazine: "Did AEG come before DNA?" First we have to know what AEG, aka N-(2-aminoethyl)-glycine, is.

Scientists believe that prior to the advent of DNA as the Earth's primary genetic material, early forms of life used RNA to encode genetic instructions. What sort of genetic molecules did life rely on before RNA?

The answer may be AEG, a small molecule when linked into chains form a hypothetical backbone for Peptide Nucleic Acids, which have been hypothesized as the first genetic molecules. (Emphasis added.)

Already the author has led readers into fantasyland, suggesting a hypothetical backbone of a hypothesized first genetic molecule. These suggestions are piled onto the long-running suggestion that an "RNA World" ruled biochemistry before DNA took over.

NASA's astrobiologists picked up the suggestion from a paper in PLoS ONE by six origin-of-life researchers from Sweden and Wyoming: "Cyanobacteria Produce N-(2-Aminoethyl)Glycine, a Backbone for Peptide Nucleic Acids Which May Have Been the First Genetic Molecules for Life on Earth."

Well, they may have been; but then again, they may not have been.

The research team did some legitimate science. They looked for AEG in cyanobacteria, and found it. But observations of AEG in living organisms doesn't help advance the suggestion that mythical life bootstrapped up to RNA, then DNA, by using AEG first. Astrobiology Magazine acknowledges the distinction: "While the analysis is certain, its significance for studies of the earliest forms of life on earth remains unclear." Then the writer employs the power of suggestion again: "Does the production of AEG by cyanobacteria represent an echo of the earliest life on Earth?"

Well, maybe it does, and then again, maybe it doesn't.

Throughout the PLoS ONE paper, between sections on real chemistry and biochemistry, the researchers tease readers with the power of suggestion: "It has been hypothesized that RNA was the primary molecule for conveyance of genetic information by life on earth prior to the evolution of DNA over 3.5 billion years ago." My oh my, who would have ever hypothesized that? Last sentence: "It is tantalizing to hypothesize that the presence of AEG in cyanobacteria may be an echo of the pre-RNA world."

Tantalizing as it may be, scientists are supposed to resist temptation. Hypothesizing is different from fantasizing. If they want to actually hypothesize this, then they need to construct a hypothesis that can be tested. However, no test is proposed.

The background here is evolutionary naturalism. A mythical AEG evolved from a chemical soup. This pre-RNA World evolved into a mythical RNA world. Then, somehow, "the advent of DNA" (unexplained) occurred to take over the job of storing genetic information. All this happened spontaneously. They're implying that the molecules did it themselves from the bottom up, without design.

Skeptics are unwelcome at this party: they're killjoys and spoilsports. They awaken the dreamer from his dream by asking hard questions:

  • How concentrated would the AEG have to be to hold useful information?
  • How would the molecules become one-handed?
  • How can RNA "take over" the genetic information in AEG?
  • How can DNA "take over" the genetic information in RNA?
  • How would mindless molecules know what "genetic information" is?
  • Since there's no natural selection before accurate replication, isn't all this highly improbable?
  • How did accurate replication emerge without error catastrophe?
  • How did the genetic molecules become isolated in containers?
  • How did the containers allow the right ingredients in while keeping toxic ingredients out?
  • How would you test this scenario without investigator interference?
  • What would you accept as a falsification of this suggestion?

Questions like these are as unpleasant as the scene in Back to the Future III where Marty tries to rouse Doc from a drunken stupor with hot sauce and a dunk in cold water.

Intelligent-design scientists would ask other questions, like: Does the AEG have a function in living cells? "The metabolic function of AEG in extant species of cyanobacteria and its potential evolutionary significance is unknown," the astrobiologists say, "although we do note that PNAs [peptide nucleic acids] have been investigated by the pharmaceutical industry as possible gene silencers."

ID researchers would pursue that angle as a possible function for these molecules. That's a testable research program. It may not be as fun as offering suggestions, but it leads to real understanding.

Image credit: Jake Bellucci/Flickr.