This article is inspired by the book “The Selfish Gene” by the well-known scientist Richard Dawkins. One of the chapters describes the idea of how the life could potentially appear and develop to the first cells and bacterias. I was so impressed by this idea, that decided to tell about it in short to my readers and subscribers of my blog.
Darwin’s theory of evolution is really a general law of the survival of the stable. The universe is populated by stable things. A stable thing is just a collection of atoms that is permanent or common enough to deserve a name. It can be Everest or Empire State Building, both last enough to be worth naming. Or it can be some class of entities, that come into existence too often to get a collective name, such as rain drops. The drop has its stable rounded shape due to the action of the aerodynamic forces. You never see square-shaped rain drops, right?
Everything you see around you is a stable pattern of atoms, even ocean waves, though their lives are short. Soap bubbles tend to be spherical because this is a stable form for thin films filled with gas. When atoms meet they may link up together forming molecules, complex collection of atoms. Molecules can be more or less stable, small or extremely large. For example, a crystal such as diamond can be regarded as a single molecule since it’s internal structure is endlessly repeated.
In modern organisms we can find incredibly complex molecules, such as hemoglobin in our blood. Hemoglobin is a protein molecule build from chains of smaller molecules, amino acids, each of them containing a few dozen atoms arranged in a precise pattern. There are 574 amino acid molecules in a hemoglobin molecule, forming a globular three-dimensional structure of bewildering complexity.
Hemoglobin illustrates the principle that atoms tend to fall into stable patterns. If a group of atoms in the presence of energy falls into a stable pattern it will tend to stay that way. The earliest way of natural selection was simply a selection of stable forms and rejection of unstable ones. There is no mystery about this, it had to happen by definition.
Among the possible chemical materials on Earth before the life were water, carbon dioxide, methane and ammonia. Chemists have tried to imitate the chemical conditions of the young Earth and put these simple substances together, and added some source of energy like ultraviolet light or electric sparks. After a few weeks of such simulation, something interesting is usually found inside: a large number of molecules more complex than the ones originally put it. In particular, scientists have found amino acids - building blocks of proteins. Thus, the existence of amino acids implies only the presence of a few simple gases in the atmosphere and some volcanoes, sunlight or thunders. More recently in the laboratory simulations of the early Earth have been found organic substances called purines and pyrimidines. These are the building blocks of the DNA, genetic molecule itself! Moreover, we now find organic molecules in meteorites and even comets.
Today large organic molecules would not last long enough to be noticed: they would be quickly absorbed by bacteria or other living creatures. But in those days these organic molecules could drift untouched in this thickening ancient soup.
At some point, a particularly remarkable molecule was formed by accident. We will call it the replicator. It may not necessarily have been the biggest or the most complex molecule around, but it had the extraordinary ability to create copies of itself. Actually, a molecule that makes copies of itself is not as difficult to imagine as it seems at first, and it only had to arise once. Imagine it as a large molecule consisting of a chain of various sorts of building block molecules. The small building blocks were in abundance in the soup surrounding the replicator. And suppose each building block can attach itself to the same kind of blocks. The attaching blocks to the replicator will have the same sequence mimicking the replicator itself. This is how crystals are formed. The two chains eventually might split apart and we get two replicators, each of which can create new copies of itself.
We can imagine a more complex possibility: each building block can attach itself not to the same kind of blocks, but to some particular another type of blocks. Then the replicator would act as a template not for an identical copy, but for a kind of “negative”, which would in its turn make a copy of the original “positive”. The modern equivalents of the replicator, the DNA molecules, also use positive-negative replication.
We get into the situation when we have a large population of identical replicas. But any copying process has an important property: it is not perfect. Mistakes happen. As mistakes were made and propagated, the primeval soup became populated by not identical copies, but several varieties of replicating molecules, all descended from the same ancestor. This makes the evolution possible. Some varieties were more stable than others, so they became more numerous because they lived longer and had more time to make their copies. But some of the rivals “species” could replicate faster than others on average, even though lived less. Others could develop some other characteristics which could help them outnumber the first two kinds of replicators.
We can now see that some varieties must actually have become less numerous because of the competition, and ultimately many of their lines must have gone extinct. They didn’t know they were struggling. But they were, in the sense that any mis-copying that resulted in a new higher level of stability, or a new way of reducing the stability of rivals, was automatically preserved and multiplied. The process of improvement was cumulative. Ways to increase stability and of decreasing rivals’ stability became more and more efficient. Some of them may have “discovered” how to break up molecules of rivals varieties chemically, and to use the released building blocks for making their own copies. These proto-predators simultaneously obtained “food” and removed competing rivals. Other replicators perhaps discovered how to defend themselves, either chemically or by building a physical wall of protein around themselves. This is how the first living cells appeared. Replicators began to construct for themselves containers/vehicles for their existence. Such containers were like survival machines. Survival machines got bigger and more elaborate, and the process was cumulative and progressive.
Four thousand million years later, what happened to the replicators? They didn’t die, but do not look for them floating in the sea. They are in you and me, they created us, body and mind. They have come a long way, and we are their survival machines.