The Origin of Life
Although popular science books peddle the idea that life started quite readily in some propitious primeval soup, any who have looked at the question at all seriously are only too aware that the origin of life poses formidable if not insurmountable problems.
In 1953 it had all looked so promising: Not only did James Watson and Francis Crick work out the double-helix structure of DNA, but in the same year Stanley Miller published the results of his famous ‘primeval soup’ experiments in which he produced some amino acids by passing an electric spark through a mixture of water vapour, hydrogen, methane and ammonia. So, just as basic genetic mechanisms were being understood, came the first clear evidence that organic compounds could arise from abiotic sources – prompting enthusiastic speculations about the origin of life.
It was recognised that amino acids are only rudimentary building blocks, but biologists were sure the rest would follow. They were confident that the origin of life could be accounted for solely in terms of physics and chemistry, and that it was just a matter of time before the whole story, from prebiology to simple organisms and then to the full array of present-day life, would be unravelled. According to Miller, biologists of the 1950s expected to be able to explain the origin of life within 25 years.
But it didn’t work out that way. In fact 40 years after his early soup experiments, Miller admitted that solving the riddle of the origin of life had turned out to be much more difficult than he or anyone else had anticipated. And now, after more than 60 years, the problem of the origin of life is just as insoluble, if not more so as we have explored various possible routes and found them to be dead ends. A clear indication that the problem is proving such an obstacle is that there is no generally accepted coherent theory for the origin of life; different groups of investigators have their preferred options, and point out the failings of others’.
So why has the bubble burst?
We have come to realise that there are some fundamental problems.
1. Even the simplest forms of life are complex on at least 2 different levels:
- biological systems comprise a complex interplay of biological macromolecules (generally proteins, often with nucleic acids also involved);
- and the individual biological macromolecules are complex, such as proteins which comprise highly specific sequences of amino acids.
This compounded complexity presents a formidable – probably insuperable – challenge to a trial-and-error origin of biological systems. Read further.
2. A prime example of this complexity is of course the interdependence of genes and proteins – that each requires the other for their production – a classic chicken-and-egg scenario. And a key feature of this interdependence is the genetic code, which is implemented by at least two layers of enzymes; which, again, would appear to make any evolutionary origin totally unrealistic. See genetic code.
Of course, various possibilities have been suggested for trying to scale the mountain; but they have all turned out to be blind alleys:
1. Because some amino acids – the building blocks of proteins – have been found in primordial soup experiments, it was hoped that polypeptides might also arise. But the conditions required for making and breaking peptide bonds (to try out different sequences) are not compatible; and in the absence of enzymes to control which reactions take place, all manner of unwanted side reactions occur.
2. Because of the difficulties with putative primordial proteins, hope has been pinned on nucleic acids, particularly RNA. But an additional problem here is that the nucleotide building blocks are even less likely to arise and more likely to degrade.
For further discussion on these see here;
and for a wider discussion of the subject see Chapter 13 ‘Chicken and Egg’ in Evolution under the microscope.
Notes display in the main text when the cursor is on the Note number.
1. Horgan J, The End of Science, Little, Brown & Company, 1996, p138.