In our lifetimes, it may not be possible to arrive at a detailed picture of how life was created on earth from organic molecules. Yet it must be remembered that our knowledge in building this picture has advanced through gigantic leaps in insight and the secrets of cellular machinery at work have gradually unfolded before our eyes. Without invoking any supernatural designer, it may be fair to say that over vast geological times (4 billion years in the case of our planet), nature might be the most intelligent designer that ever existed, as the evolution of life unfolded.
Perhaps the creation of the first genome (a complete set of genes that sustains life) was the most complex leap ever in the process. Creation of human beings from our earliest mammalian ancestor by contrast, is seemingly far less complex as the genes mutated, shifted, rearranged and natural selection helped to consolidate the process.
By and large, amongst scientists involved in working out the chemical beginnings of life, the idea that at some stage in the primordial oceans life consisted solely of RNA molecules, has almost universal support at present. By the 1980’s, the picture of a RNA World ( a term coined by Walter Gilbert, Harvard chemist, nearly 25 years ago) was firmly in place, but a few important details were left to be filled in. After decades of searching, more and more RNA molecules were found in nature which acted both as carriers of genetic information as well as acted themselves as enzymes to aid their own replication and could therefore be considered self propagating molecules. The RNA enzyme first discovered by Robert Cech, University of Boulder Colorado (who won the Nobel Prize for it in 1989), comes from a strange one celled animal Tetrahymena, is capable of swapping bits of information with other RNA enzymes/sequences, and it can be considered to equivalent of having sexual reproduction.
— Michael Denton (Evolution: A Theory In Crisis)
Ed. comment : Perhaps we are quite close to recreating this miracle!
As the original inhabitants have of the RNA world have largely disappeared, for the past decade, scientists have been artificially trying to ‘evolve’ RNA sequences in the laboratory starting with short chains. By 2001, the first prototype called the R18 had evolved which of the partially replicate itself. In 2011, Philipp Holliger and colleagues at Cambridge, UK, have reported the most advanced RNA enzyme that has evolved on its own as yet in the laboratory- the tC19Z, which replicates up to half of its own length. We are getting quite close to the fully replicating RNA strand in the laboratory, which can be considered the first experimental species of self-evolved RNA that could lead an independent life given the right circumstances.
Our lab experiments as well as chemical analysis of asteroids that have arrived on Earth have demonstrated that all the constituents that would successfully lead to an RNA world can be found in nature under the conditions that we think were present in the early part of the Earth’s atmosphere and oceans. There are still many questions that remain to be answered before we have a complete model of the RNA world, some of which date back even further to the rise of RNA itself. One fundamental problem has been a satisfactory explanation of how the four activated nucleotides (five for DNA), which are the building blocks of RNA itself, were self-assembled. John Sutherland of Cambridge UK has so far only replicated two of them in the laboratory, and is reportedly ‘closing in’ on the other two. Jack Szostak of Harvard has not only demonstrated that primordial clay that promotes RNA chain formation not only encourages cell membranes to from around these chains, he has actually grown proto-cells that carry RNA and even divide without any of the modern cell division machinery.
We do not know for sure yet whether RNA based ‘life’ evolved around the hydrothermal vents on the ocean floor or in cold ice (both are plausible scenarios with their own advantages). But it is not unlikely that we would see life emerge from primordial chemicals in the lab under right conditions under our very eyes. The miracle of life rather, as despite the small odds of it happening it happened !
Adapted from ‘First life: The search for the first replicator’ by Michel Marshall.
Link to the article : http://www.newscientist.com/article/mg21128251.300-first-life-the-search-for-the-first-replicator.html?full=true
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