The Origin of Life by S. Shafqat
The Origin of Life by S. Shafqat
On a warm and humid day approximately 3.8 billion years ago, with the adolescent Earth cooling down into its permanent features and with rain and lightning dominating the skies, some random molecules came together in a primordial water-soup – perhaps in the sea, perhaps in some pond or lake on a stretch of land – and found that they were better off together than alone. This spontaneous assembly harnessed energy from its surroundings and managed to make another of its own kind. And with this the game of life was afoot. Between that original self-replicating assembly and us is evolution, something we have been able to decipher and understand. But between that cell-like assembly and the soupy lifeless mixture that existed before it lies perhaps the most unbridgeable chasm ever contemplated by human intellect: the emergence of life.
The origin of life, clearly one of the most momentous events in the history of the universe, remains a process of which we know very little. Nevertheless, this mystery generates the most deep and intense fascination. Although no one knows the truth yet, most people who think seriously about this problem agree on the following basic facts:
1. The origin of life happened. That is, there was a time in the universe when there was no life and then there was life. It was a distinct event.
2. It was a unique event. That is, it happened only once. After that first time, all living matter has come from other living matter.
3. It happened against great odds. The second law of thermodynamics holds that a system left to itself increases in entropy (i.e., becomes more disordered). Random molecules somehow organizing themselves into orderly self-replicating assemblies violate this law.
Logically speaking, there are really only two possibilities. Either life arose from a purely physical phenomenon, or it arose through intelligent intervention. Intelligent intervention is usually taken to mean something supernatural, something beyond physical reality, like God. There is also a subview to this which holds that life on Earth was planted from outer space, but that leaves unaddressed the problem of how life arose in outer space in the first place, so this line of thinking really does not add anything to the discussion.
There are problems with both the physical view and the supernatural view.
The biggest problem with the physical view is that no one has been able to replicate the origin of life. After all, if it is simply a question of bringing together the right chemicals and physical conditions, the event should be reproducible. Indeed, given the advanced state of biological knowledge today, the inability of laboratory scientists to synthesize life appears especially remarkable. It is as if we could take apart a watch and know precisely which component fitted in where, but were still unable to put it back into working order. Although the quest remains elusive, proponents of this view say that they just need to know more about life itself as well as about primordial conditions on Earth before the genesis of life can be recreated in the laboratory. Opponents say that the origin of life can never be reproduced by man because it was a supernatural event.
The problem with the supernatural view is that since it has not helped us in any other aspect of understanding the natural world, it is unlikely to be helpful in this case as well. Proponents of this view say that there is so far no evidence that would directly falsify this hypothesis, so it remains a viable possibility. Opponents say that reductionism – the scientific approach that reduces all observed phenomena to physics and chemistry – has so far been hugely successful in explaining the phenomenon of life, so this is the right approach to understanding the origin of life.
There is not much room for discussion as regards the supernatural view, but regarding the reductionist view, several interesting points can be made. In the first place, since anythingâ€™s possible, it is certainly conceivable that life spontaneously arose from non-living matter. The law of entropy need not be violated if the generation of order at one point in the universe gets counterbalanced by the generation of even greater disorder at another point, so that the universe as a whole tends towards disorder. Secondly, there are two tantalizing pieces of scientific evidence that support the reductionist view, namely the Miller-Urey experiments and the catalytic properties of ribonucleic acid (RNA). Let us look at these individually.
In 1953 Stanley Miller, working in the laboratory of Nobel laureate Harold Urey at the University of Chicago, showed that complex organic molecules can be produced from simple chemicals under certain conditions. Miller passed electrical discharges through a mixture of methane, ammonia, steam and hydrogen and, after several days, isolated a complex mixture of organic compounds from the resulting brew, including several of the biological amino acids that are routinely found in living tissue. Millerâ€™s conditions resembled the known atmosphere of Jupiter, which was considered the best guess for what primitive conditions on Earth may have been like nearly four billion years ago when life is estimated to have emerged on our planet. The Miller-Urey experiments have been widely reproduced, sometimes with interesting variations. For example, the absence of oxygen from the starting mixture is important – in the presence of oxygen, no amino acids are generated. Tantalizing as these results are, however, the production of amino acids is not the same as the production of life. The creation of life â€˜in a test tubeâ€™ remains the holy grail of this approach.
The catalytic properties of RNA are exciting because they give this crucial biological molecule the dual properties of being a carrier of genetic information as well as an enzyme, making it an ideal candidate for being the first step in the origin of life. The phenomenon of life relies on two critical kinds of molecules, informational molecules and catalytic molecules. Informational molecules carry and transmit genetic information and encode the design blueprint for all living organisms. Catalytic molecules facilitate all the chemical reactions that make life go on. The known informational molecules are DNA and RNA, both nucleic acids; the known catalytic molecules are enzymes, which are proteins. One of the conceptual hurdles in origin-of-life thinking has been the need to postulate at least two different kinds of molecules – nulceic acids and proteins – coming together on the primitive Earth and becoming spontaneously organized into self-replicating assemblies. There is now good evidence that RNA itself has some enzymatic properties and can catalyze certain chemical reactions. Thus it is plausible that the spontaneous production of RNA was the only real hurdle to be overcome for life to emerge. This, too, is tantalizing but, beginning from RNA alone, nobody has yet been able to get to life as we know it.
A related, and perhaps even more intensely fascinating, field is the search for life elsewhere in the universe. If life is found on other planets, it will be a strong endorsement for the reductionist view because it will suggest that, as with any other physical phenomenon, so long as the conditions are right, life is born. So far there is no convincing evidence of extraterrestrial life, however. Even so, absence of evidence is obviously not evidence of absence.
So which view is the correct one ?
It is clear that all the major intellectual victories in modern science are attributable to reductionism. We have understood the most about ourselves and the world around when we have worked under the assumption that these things can in fact be understood, in the most simple and verifiable terms. If we invoke supernatural explanations for our observations, then there is no motive to try and understand them because we are effectively conceding that these phenomena lie forever beyond human comprehension. In the matter of the origin of life, however, the choice is hardly that simple. Biologists today have comprehensive knowledge of the inner workings of cells and know the complete genetic blueprint of several bacteria (the simplest independent life forms) with 100% accuracy. Therefore, if their view is to be unquestionably accepted, reductionists can reasonably be expected to show us that life can be synthesized from non-life. This has yet to be done, so it may be said that the jury is still out. Richard Fortey, the famous English paleontologist, has likened the promises of synthesizing life by modern scientists to the claims of turning copper into gold by the alchemists of yesteryears. Just a little more knowledge and the right conditions, the alchemists would say, but it never happened. Could it be that the modern biologists who have taken up the challenge of converting dust to life are the alchemists of today ?
Regardless of the data limitations in this problem, considerations about how life began remain an area of intense speculation. This is the intellectual nexus of cosmology and biology, where human self-perception must confront modern scientific doctrines. Although it is at present firmly the province of speculation, how delicious to contemplate that it may not always be so!