Craig Venter was interviewed by Charlie Rose last week, repeating highlights from his recent book “Life at the Speed of Light”. As one of these, Craig told Charlie that if we were just to send a DNA sequencing instrument to Mars, sequence the DNA of Martians living there, radio that sequence back to Earth, and synthesize the Martian DNA here, then we could have Martian life on Earth without needing to do the rocket science needed to actually send a physical specimen of Martian life from Mars back to Earth.
Radio waves travel, of course, at the speed of light. Hence: life at the speed of light.
No one is a bigger fan of Craig than I am. However, Craig would be a better synthetic biologist if his enormous imaginative powers included imagination within organic chemistry.
Basically, Craig has caught himself in the “Earth-o-Centricity” trap. The trap catches those who assume that the chemical structures of the molecular parts of life throughout the universe are the same as the molecular parts of life on Earth.
Ask yourself a simple question: What makes us certain that Martian life has DNA? After all, the RNA-World hypothesis holds that life on Earth, at least for part of its early natural history, used RNA rather than DNA as its genetic material. If instead of going to Mars, we were to send Craig’s sequencer back in time to sample the life on early Earth expecting to find DNA, that hypothesis (if true) would imply a disappointment.
Nor is it beyond possibility that another biopolymer having a quite different backbone structure could support genetics. According to the “polyelectrolyte theory of the gene”, the only “universal” for a genetic biopolymer is a repeating backbone charge.
And even if Martians living today do have DNA, what makes us think that its building blocks have the same structure as the building blocks of terran DNA? Researchers in my laboratory have shown that alternative nucleobases can serve the roles of G, A, C, and T in natural DNA. What if Martian life used these?
If aliens have different biochemistries, Craig’s proposal is, well, problematic. The polymerase chain reaction (PCR) works only if it is done with enzymes and substrates appropriate for the genetic biopolymer being amplified. Considerable amount of work, some in our laboratories, shows that the enzymes that PCR amplify terran DNA do not work so well with structurally modified DNA, even if that structural modification is small. Likewise, the triphosphates included in a typical PCR kit (the terran G, A, C, and T) work only if Martian DNA is also built from G, A, C, and T).
If Martian genetics were based on a molecule whose structure differed even slightly (and certainly if that structure different dramatically) from the structure of DNA and RNA, Craig’s mission would be a flop, perhaps not a cosmic flop but, at least, and interplanetary flop.
And unfortunately, the outcome could be considerably worse. Absent exceptional cleanliness, any sequencer that we send to Mars would carry with it a few terran microbes, microbes having exactly the DNA that Craig’s sequencer would most efficiently amplify and sequence. Unless Martian genetics had exactly the same biomolecules as terran, his sequencer would sequence these hitchhiking microbes. At the speed of light, we would recover the DNA of a terran organism that we ourselves had just sent to Mars. Bummer.
Earth-o-Centricity afflicts everyone. Like the screen writers for low budget science fiction movies, where all of the aliens appear to be Hollywood actors wearing prostheses.
The central challenge when setting out to discover alien life boils down to two simple chemical facts: It is easy to detect a molecule whose structure is known. It is difficult to detect a molecule whose structure is not known. And unless Martian biomolecules are like terran biomolecules, they will be difficult to detect. Even if we are sitting on a pile of them.