At the Vanilla Bean this afternoon I read that in 1837 Charles Darwin scribbled in his notes that “life originated only once.” This was a remarkable thought-provoking idea during that time of civil unrest much about the economic issues discussed today here at the Cafe – the economic breach between the common folk and the wealthy gentry.
No, Darwin wasn’t thinking about a divine event that happened 5 or 6000 years before. He was only six months back from his five year voyage on the Beagle around the world, still a rare feat back then. I haven’t read enough to learn how he concluded that “life originated only once” but he is clearly right. If ‘life’ evolved from non-life more than once after a long time span between the two events, we probably would not recognize it and this second lifeform would not likely survive long enough to be detected.
This is some of the thinking I had to deal with when trying to write a three page essay for a client’s application to the EPA that had to do with the danger of creating unwanted new life forms as the result of escaped recombinant DNA.
This original event pondered by Darwin was an improbable stochastic event which once begun would likely out compete and erase any unlikely later origin-of-life events. How do we know that this happened only once? In 1964, the genetic code was systematically cracked in Marshall Nirenberg’s lab at NIH. This was the genetic code for the E. coli bacterium. It did not take even a decade to determine that humans and all other life forms had the same genetic code. This is consistent with “life originating only once” … some 3 billion years ago.
In my own bench mark discovery my colleagues at Max-Planck and I sequenced the human protein beta-actin, the most abundant protein in all replicating eukaryotic cells. This protein is fundamental to all eukaryotic cell life (cells with a nucleus). We had other reasons for wanting to determine the sequence of this protein, but what came out was that this protein is essentially the same in sequence as actin in yeast, the lowest eukaryotic life form. This demonstrated that this protein was the highest conserved protein in evolution from yeast to humans. A few years later I cloned the human beta actin gene and proved to myself that the genetic code was correct (in 1982) in that I was able to predict the mutation that I had discovered in this protein and its gene in terms of the gene’s altered nucleic acid sequence, and then found it to be true.
Oddly, it was only a year ago when writing that three page essay I mentioned that I discovered a not well-known paper that presented the discovery of an actin gene in a strain of cyanobacterium, a photosynthetic bacterium that lives in the ocean. This is the only known example of such an occurance. Since the actin gene and its protein is now well understood in terms of its roll in higher life forms it could be concluded that the actin gene escaped from a marine invertebrate into the cyanobacterium probably while the bacterium was passing through the gut of the marine invertebrate – a stochastic event. So I was able to make a strong argument that there has been no unwanted escape of a recombinant gene from an engineered organism. But I had to end with the caveat that the most highly conserved gene in eukaryotic life escaped into a bacterium in a millennial timeframe (there are rare examples of transkingdom transfer of other genes). Heck, our mitochondria and plant chloroplasts are assimilated bacteria. What is even more surprising is that cyanobacterium expressing actin survived and competed within the biosphere so that it could be discovered. So it’s not only the mutations that occur in genes that spur evolution and natural selection, it’s also transkingdom transfer of genes between distant organisms.
I had the chance to meet Carl Sagan when he visited Linus Pauling at our institute in Palo Alto in 1984 or 85. Anne Druyan was there too. He was trying to raise money for the search for extraterrestrial intelligence (SETI). When I put the thought that “life originated only once” together with the idea that there might be extraterrestrial life, I can only conclude that if it exists elsewhere it will be nothing like life on Earth. In fact, there may be good reason not to try and contact them.