Spontaneous Generation

The spontaneous generation is the appearance of an living being without ascending.

The belief in the spontaneous generation formed part of the common direction a long time, because the appearance of living beings where one did not see any is a phenomenon of current observation. During millenia, the men had realized that their livestock needed a coupling to produce the small ones. The cows could not have calves without bull, the ewes not of lambs without ram, etc Nevertheless, for the small animals, one continued to believe that small mice could be born spontaneously from a heap from rags and maggots to leave a piece of meat. The micro-organisms, microbes and yeasts, seemed the obvious product of a spontaneous generation.

The careful experiments of Pasteur at the 19th century clearly established that in all the supposed cases of spontaneous generation, there was in fact of the germs, of eggs, at the origin of the appeared living beings. In an isolated medium and suitably sterilized, the life does not appear spontaneously, at least not on typical time and space scales of a laboratory. The questioning of the spontaneous generation played a great part in measurements of hygiene and Asepsie against the development of the diseases. Felix-Archimedes Pouchet inventive of the Heterogeny, with which Pasteur was opposed to the Academy of Science remained until its death convinced of the spontaneous generation.

The assumption of the spontaneous generation today lost any scientific credit, except within the framework of research on the origin of life on ground. An original spontaneous generation is the most plausible solution with the problem of the regression ad infinitum. The conditions of the primitive Ocean, the matter and the serviceable time, make that it is not possible to extend the negative results of Pasteur to the question of the origin of life.

The problem of the regression ad infinitum

The problem of the regression ad infinitum is that of the Paradoxe of egg and the hen. The origin of a hen, or any Pluricellular living being , is a egg. The origin of a hen egg is a hen. Who was the first there? One can suppose that there is no first, that the hens and the eggs followed one another without there never being beginning.

In this form, this assumption is incompatible with what one knows of the history of the life about the Ground. It is not contestable that the living beings of today evolved/moved starting from primitive forms Unicellulaire S. But one could still accept a regression ad infinitum of the unicellular ones. It is not very plausible, initially because the Earth exists only since 4,5 billion years. It could be sown outside but a space flight would be rather incredible all the same. At all events, the assumption of the regression ad infinitum runs up against the temporal finitude of the Universe. It imposes that time does not have a beginning, which is logically possible, but incompatible with the data of observation, on the direction where it is impossible that our universe is remained such as it is since an eternity (an infinitely long time). Is there a direction perhaps to ask what there was before the great initial explosion (the Big Bang), but unless questioning all that one knows, it is not possible to believe that unicellular existed at the time of the first moments of the known universe.

To escape the difficulties ad infinitum from the regression without giving up the theories, it should be supposed that the life can appear spontaneously without transgressing the known laws. That resulted in supposing that in an ocean without life, of the unicellular prebiotic molecules then primitive ones could appear.

The Chance and the Complexity

The theory of the spontaneous generation seems to run up against the complexity of the living beings. Even most elementary, like the Bacterium S, are wonders of molecular technique. The molecules many, complex and are remarkably well adapted to their function. Very light differences in the fitting of the thousands of atoms whose these molecules are made up and all the bacterium can cease functioning. It does not appear conceivable, without resorting to the miracles, that such complicated molecules, and a fortiori the bacteria of which they are the components, can be appeared simply by testing all the possible combinations in an ocean of simple molecules; the age of the Univers would be one very insufficient duration. If molecules randomly are mixed, one obtains a formless mass and not an living being.

However, it is important to realize well that we, the men, who we question on so-called “the miracle” of the appearance of the life, we are descendants of these improbable but however possible primitive organizations. And it is there that it is necessary well to make the difference between an impossible event and an improbable event. An impossible event never arrives, even with billion “tests”. An improbable event, on the other hand, will occur but statistically all the more seldom as it is improbable. Thus, an event which has a chance on a billion to occur, will have relatively many chances to occur with several billion “tests”.

If one now considers the astronomical number of planets in the universe, on the large majority of these planets, where the life did not appear, or then where the life appeared but did not evolve/move as much as on Earth, there are beings questioning themselves on the “miracle” of the hazardous organization of the molecules, organization which carried out, with the million and the million years, with them?

It is probable in a measurement which we do not know if one considers the gigantic quantity of stars being able to join together planets around them only on the level of the galaxy in which we live.

There thus were a very high number of “missed tests”, planets without life, and the Earth, like probably much of another planets, where it appeared, by chance. The very improbable event of the life had “granted tests enormously”; this event thus arrived. This mechanism does not require nor does not bar from a divine intervention.

Our capacities to fill with wonder to us in front of the beauty at the life coming from its emergence, since we are one of very, very remote descendants, it does not have there in the final analysis what to be astonished that we are there.

Numerical experiments of Kauffman

That complex forms cannot have a random origin was a principle very generally accepted. Stuart Kauffman is the first to have questioned it following numerical experiments. He studied the dynamics of cellular networks of automats generated in a random way. He then observed that animated stable forms of a periodic movement appeared spontaneously, whatever the initial conditions. He thus saw complex and durable forms generated in a purely random way. He quickly understood that its observation renews in a very original way our ways of explaining the phenomena and that he could apply it to the question of the origin of life. He spent a few years before making it accept by other scientists.

Autocatalytic networks

When many different molecules are put in presence, one can describe chemical dynamics by a network. Each species of molecules is connected to the other species with which it reacts. Such a network can have autocatalytic loops , i.e. a molecular species, call has, supports it, or Catalyze, of the chemical reactions which will lead to the production of molecules of type A. Such a loop is potentially explosive, because there is a snowball effect, but if the species from which has is produced are in limited quantity, the self-production of has itself is limited.

The living beings are always autocatalytic networks. All their molecules (DNA, Protein S and others) react with the molecules introduced (the Aliment S) to produce molecules similar to themselves. The Plante S are even able to use the sunlight to this end.

By studying models, Kauffman established that under rather general conditions a network of chemical reactions contains necessarily autocatalytic networks. It is enough that the network is sufficiently bulky, that the molecular species are the sufficiently many and reactive ones with respect to the others.

The primitive ocean was a mixture of water and molecules organic. Those can be very complex and very reactive. It thus seems that the primitive ocean satisfied the conditions of the theory kauffmanienne of the spontaneous generation.

The autocatalytic networks explain the reproduction of the molecules but alone they are not enough to explain the reproduction the unicellular ones.

Spontaneous formation of the blisters

It is enough to agitate a soapy Eau to obtain foam. The sea foam is formed in the same way, all the more easily as water is dirtier. One explains it starting from the character Amphiphile certain molecules. A molecule is absorbent if she “prefers” being in water that in oil, i.e. so spontaneously, because of the laws of the Physique statistics, they concentrate more in water in oil. It is Hydrophobe, or lipophilic, in the opposite case. Certain molecules, such as those of the soap, are lengthened with an absorbent end and the other hydrophobic subject, this is why they are known as amphiphilic. When they are put in solution in water, they then form spontaneously many structures which can be very complex and in particular the double-layered ones which is folded up in blister S. a Bicouche is a wall, plunged in the water, of which the two faces are made up of absorbent heads, the hydrophobic ends being gathered inside the double-layered one. A blister is a small bag full of water, which floats in the water, and whose wall is double-layered.

The cells of the living beings are very elaborate blisters. Their wall is primarily double-layered but it is much more complex than the walls of the blisters in soapy water. The interior of the cell especially is very different from its outside, which is not the case of the blisters only one forms by agitating a dirty water.

First cells

Very many blisters could be formed in the primitive ocean, as easily as today the scum of the sea. That such a blister is the place of autocatalytic reactions is completely plausible. If its walls are such that they let penetrate the small molecules necessary to the reproduction of the grosses, then one obtains, by the simple play of the physical and chemical laws, an organization able to feed and grow. Of course the blisters are not always equipped with such a capacity, but if they rather many and are diversified enough such a event is perhaps not completely improbable.

So that a cell is alive, it is not enough that it is able to grow, it is necessary still that it can reproduce. The most probable destiny of a blister in growth is to explode and thus to disperse all its contents, which amounts dying. But one can suppose that certain blisters incorporated in their wall of the molecules which make it suitable for form new blisters, via protuberances which are detached for example. This part of the scenario suggested here of the origin of life is perhaps not very plausible but it is not either completely excluded, especially if one thinks of the diversity of the two-dimensional structures which can be formed spontaneously on the double-layered ones.

If a blister is able to grow while feeding and to reproduce, by forming protuberances, then it is a primitive living being. It with the essential property of the living beings, capacity to reproduce when it is placed in a suitable environment. One can then suppose that such a blister is the ancestor of all the living beings which exist today.

The origin of the DNA and the genetic code

The first autocatalytic networks were not as elaborate as those of today, founded on the very complex machinery of the DNA, the Ribosome S, the genetic Code and proteins. But the primitive living beings were able to evolve/move. Their autocatalytic networks could be modified by the incorporation of new molecules, absorptive in an exceptional way. Such modifications are héritables, because once a molecule is incorporated in an autocatalytic network, it becomes able to reproduce. The conditions of the evolution by the Natural selection, such as they were stated by Darwin ( the origin of the species ), are thus met: random variations héritables and competition within a population for the access to the resources. The primitive cells most powerful are those which reproduced best and they tended to dominate the population. One can then suppose that the primitive living beings evolved/moved. Their rudimentary autocatalytic techniques improved until reaching a point of quasi-perfection, namely the techniques of Réplication of the DNA and manufacture of the proteins which are had since billion years by all the living beings.

How to know if this theory is true?

One cannot go up the time to go to see how was the primitive ocean and how it evolved/moved. But one can find testimonys indirect. The past leaves traces in the present. If there are the good tools, theoretical and observational, one can deduce the past as from the present. For example, the autocatalytic techniques of today are to some extent fossilized since of the billion years, since they or little did not evolve/move. They thus inform us about a very remote past. By combining this information with others, one can hope to go up even further in time. Experiments in laboratory of prebiotic Chimie can bring invaluable information.

Biology and cosmology

The theory of the spontaneous generation leads to a unified vision of the Matière and Vie. The appearance and the evolution of the life are conceived there like consequences necessary of the Dynamique of the universe. As soon as adequate conditions are met (water Liquide, which supposes a adequate Température, and organic molecules in abundance, in other words, water salts), the matter expresses its capacity to generate the life. In a metaphorical way, one can say with Kauffman which the living beings can on their premises feel in the universe, because the matter is as the nourishing earth which gave us the life. In the first time of its existence the Earth was a still fluid and extreme matter sphere, permanently bombarded by meteorites of all sizes. The elements which constituted it (like metals and the mineral substances which enters the composition of the rocks) formed a rather homogeneous mixture.

Sources

Stuart Kauffman, At home in the universe
John Maynard Smith, Eörs Szathmary, the origins of life

See too

Experiment of Miller
Origins of life
Synthesis of the proteins
Vitalism
Abiogénèse

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