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Science Frontiers ONLINE No. 92: Mar-Apr 1994 |
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The World Before Our World
Genetically speaking, modern terrestrial life is bilingual in the sense that it employs two chemical languages. Function is written in the 20 amino-acid "alphabet" of proteins, while information is conveyed in sequences of four nucleotide "letters" called codons. We need go no further with the genetics lesson because our purpose here is to speculate a bit about the monolingual world that is believed to have preceded ours.
This older world is commonly termed the "RNA World." It was and is monolingual because both function and information are carried on a single molecule. It is customary to call the RNA World "prebiotic," meaning that it was all chemistry and no life. But, one does wonder whether that was all there was to it. Catalysis and replication of genetic information occurred in the RNA World. What besides a chemical soup might have existed before "life-as-we-know-it" arrived upon the scene? A science fiction writer like H.P. Lovecraft could certainly come up with an ominous entity based upon RNA alone.
Be that as it may, a book is now on the market bearing the title The RNA World (R.F. Gesteland and J.F. Atkins, eds., Cold Spring Harbor Laboratory Press, 1993) Nature reviewed the book in its January 20 issue. In addition, the RNA World was discussed recently in Science. We now extract one nugget from each of these two sources.
From Nature's review. Humans are more primitive than microorganisms in the sense that we still retain cumbersome introns (nonsense DNA) in our genes, while lowly microorganisms have been able to eliminate them.
From Science. No one seems to have a clue about where RNA came from. C. de Duve ventured that:
"...the emergence of RNA depended on robust chemical reactions -- it is wrong to imagine that some fantastic single accidental event supported the development of the RNA World."
In connection with the generally accepted idea that the evolution of RNA must have taken hundreds of millions of years:
"...de Duve suggested that, on the contrary, for such a complex chemical process to succeed it must have been relatively fast in order to avoid decay and loss of information."
(Brenner, Sydney; "The Ancient Molecule," Nature, 367:228, 1994. O'Neill, Luke, et al; "What Are We? Where Did We Come From? Where Are We Going? Science, 263:181, 1994.)
Comment. O.K. There's the RNA World, then came ours. Will another kind of "world" succeed ours? Has it already?