There must have been a long and complicated transitional stage between the nonliving and the first truly living thing, an extended chronology of events unlikely to be preordained
in its myriad details. A law of nature could not alone explain how life began, because no conceivable law would compel a legion of atoms to follow precisely a prescribed sequence of assemblage.So,although complying with the laws of nature, the actual route to life must have owed much to chance and circumstance—or contingency, as philosophers call it.
Or there was a intelligence doing the job. Why excluding that alternative first hand ?
Inside each and every one of us lies a message. It is inscribed in an ancient code, its beginnings lost in the mists of time. Decrypted, the message contains instructions on how to make a human being. Nobody wrote the message; nobody invented the code. They came into existence spontaneously. Their designer was Mother Nature herself, working only within the scope of her immutable laws and capitalizing on the vagaries of chance. The message isn’t written in ink or type, but in atoms, strung together in an elaborately arranged sequence to form DNA, short for deoxyribonucleic acid. It is the most extraordinary molecule on Earth.
Wow. What a statement of faith, presented as if it were a consumed and brute fact. How can someone come to such a contradictional conclusion ?
Although DNA is a material structure, it is pregnant with meaning. The arrangement of the atoms along the helical strands of your DNA determines how you look and even, to a certain extent, how you feel and behave. DNA is nothing less than a blueprint—or, more accurately, an algorithm or instruction manual—for building a living, breathing, thinking human being.
Where does biological information come from?
DNA stores the information needed to construct and operate the organism. One aspect of the mystery of biological order can therefore be expressed by the question: where does biological information come from? Communication theory—or information theory, as it is known today—says that noise destroys information, and that the reverse process, the creation of information by noise, would seem to us a miracle. A message emerging on its own from radio static would be as surprising as the tide making footprints on the beach. We are back with the same old problem: the second law of thermodynamics insists that information can no more spring into being spontaneously than heat can flow from cold to hot.
The solution to the problem may once again be found in the fact that an organism is not a closed system. The information content of a living cell can rise if the information in its surroundings falls. Another way of expressing this is that information flows from the environment into the organism.Life avoids decay via the second law of thermodynamics by importing information, or negative entropy, from its surroundings. The source of biological information, then, is the organism’s environment. Both metabolism and reproduction are driven by information flow from environment to biosystem.Successful mutations are those that are better adapted to their
environment, and it is therefore the environment that provides—or, more accurately, selects—the information that ends up in the DNA. So the environment feeds the information into the genetic message via natural selection
Incredible. How does that make sense ?
We will not be able to trace the origin of biological information to the operation of local physical forces and laws. In particular, the oftrepeated claim that life is written into the laws of physics cannot be true if those laws are restricted to the normal sort, which describe localized action and proximate forces. We must seek the origin of biological information in some sort of global context. That may turn out to be simply the environment in which biogenesis occurs. On the other hand, it may involve some nonlocal type of physical law, as yet unrecognized by science, that explicitly entangles the dynamics of information with the dynamics of matter.
Although biogenesis strikes many as virtually miraculous, the starting point of any scientific investigation must be the assumption that life emerged naturally, via a sequence
of normal physical processes.
No !! There is no reason to exclude a priori one of the two possible mechanisms.....
Whatever the precise chemical sequence may have been, life must have formed as a result of some sort of molecular self-assembly.
That would be the case if no creator was around.....
Two major obstacles stand in the way of further progress towards life in a primordial soup. One is that in most scenarios the soup is far too dilute to achieve much. Haldane’s vast ocean broth would be exceedingly unlikely to bring the right components together in the same place at the same time. Without some mechanism to concentrate the chemicals greatly, the synthesis of more complex substances than amino acids looks doomed
But now we hit a snag. The second step on the road to life, or at least the road to proteins, is for amino acids to link together to form molecules known as peptides. A protein is a long peptide chain, or a polypeptide. Whereas the spontaneous formation of amino acids from an inorganic chemical mixture is an allowed downhill process, coupling amino acids together to form peptides is an uphill process. It therefore heads in the wrong direction, thermodynamically speaking. Each peptide bond that is forged requires a water molecule to be plucked from the chain. In a watery medium like a primordial soup, this is thermodynamically unfavorable. Consequently, it will not happen spontaneously: work has to be done to force the newly extracted water molecule into the watersaturated medium. Obviously peptide formation is not impossible, because it happens inside living organisms. But there the uphill reaction is driven along by the use of customized molecules that are pre-energized to supply the necessary work. In a simple chemical soup, no such specialized
molecules would be on hand to give the reactions the boost they need. So a watery soup is a recipe for molecular disassembly, not self-assembly.
To be sure, there would have been no lack of available energy sources on the early Earth to provide the work needed to forge the peptide bonds, but just throwing energy at the problem is no solution. The same energy sources that generate organic molecules also serve to destroy them. To work constructively, the energy has to be targeted at the specific reaction required. Uncontrolled energy input, such as simple heating, is far more likely to prove destructive than constructive. The situation can be compared to a workman laboriously building a brick pillar by piling bricks one on top of another. The higher the pillar goes, the more likely it is to wobble and collapse. Likewise, long chains made of amino acids linked together are very fragile. As a general rule, if you simply heat organics willy-nilly, you end up, not with delicate long chain molecules, but with a tarry mess, as barbecue owners can testify.
It is true that the second law of thermodynamics is only a statistical law; it does not absolutely forbid physical systems from going “the wrong way” (i.e., uphill). But the odds are heavily weighted against it. So, for example, it is possible, but very unlikely, to create a brick pillar by simply tipping a pile of bricks out from a hopper. You might not be surprised to see two bricks ending up neatly on top of one another; three bricks would be remarkable, ten almost miraculous. You would undoubtedly wait a very long time for a ten-brick column to happen spontaneously. In ordinary chemical reactions that take place close to thermodynamic equilibrium, the molecules are jiggled about at random, so again you will likely wait a very long time for a fragile molecular chain to form by accident. The longer the chain, the longer the wait. It has been estimated that, left to its own devices, a concentrated solution of amino acids would need a volume of fluid the size of the observable universe to go against the thermodynamic tide and create a single small polypeptide spontaneously. Clearly, random molecular shuffling is of little use when the arrow of directionality points the wrong way.
There is a more fundamental reason why the random self-assembly of proteins seems a nonstarter. This has to do not with the formation of the chemical bonds as such, but with the particular order in which the amino acids link together. Proteins do not consist of any old peptide chains; they are very specific amino-acid sequences that have specialized chemical properties needed for life. However, the number of alternative permutations available to a mixture of amino acids is superastronomical. A small protein may typically contain a hundred amino acids of twenty varieties. There are about 10 (which is one followed by 130 zeros) different arrangements of the amino acids in a molecule of this length. Hitting the right one by accident would be no mean feat
Getting a useful configuration of amino acids from the squillions of useless combinations on offer can be thought of as a mammoth information-retrieval problem, like trying to track down a site on the Internet without a search engine. The difficulty can be expressed in thermodynamic terms by recalling the connection between information and entropy explained in chapter 2. The highly special information content of a protein represented by its very specific amino-acid sequence implies a big decrease in entropy when the molecule forms. Again, the mere uncontrolled injection of energy won’t accomplish the ordered result needed. To return to the bricklaying analogy, making a protein simply by injecting energy is rather like exploding a stick of dynamite under a pile of bricks and expecting it to form a house. You may liberate enough energy to raise the bricks, but, without coupling the energy to the bricks in a controlled and ordered way, there is little hope of producing anything other than a chaotic mess. So making proteins by randomly shaking amino acids runs into double trouble, thermodynamically. Not only must the molecules be shaken “uphill,” they have to be shaken into a configuration that is an infinitesimal fraction of the total number of possible combinations.
Pluck the DNA from a living cell and it would be stranded, unable to carry out its familiar role. Only within the context of a highly specific molecular milieu will a given molecule play its role in life. To function properly, DNA must be part of a large team, with each molecule executing its assigned task alongside the others in a cooperative manner. Acknowledging the interdependability of the component molecules within a living organism immediately presents us with a stark philosophical puzzle. If everything needs everything else, how did the community of molecules ever arise in the first place? Since most large molecules needed for life are produced only by living organisms, and are not found outside the cell, how did they come to exist originally, without the help of a meddling scientist? Could we seriously expect a Miller-Urey type of soup to make them all at once, given the hit-and-miss nature of its chemistry?
Life as we know it requires hundreds of thousands of specialist proteins, not to mention the nucleic acids. The odds against producing just the proteins by pure chance are something like 1O^40000 to 1.