The Origins of Life and the Diversity of Living Beings
If we are to believe certain researchers and their statements concerning the phenomenon of life, there are no more secrets left to discover today “The origins of life no longer form the subject of laboratory investigation”, stated an eminent specialist in molecular biology in 1972. Always assuming these words still carry a meaning, we may conclude that life does not contain any facts we do not know. In reality, however, the situation is quite different, and there are plenty of mysteries that still surround the origins of life.
Ingenious experiments have for many years been repeatedly performed by biochemists and biophysicians in an attempt to prove the possibility of spontaneously obtaining infinite quantities of certain chemical compounds found in cells that are structurally highly complex. The scientists in question are of the opinion that due to favourable physical influences, the compounds were able spontaneously to combine together in an organized fashion, and by uniting, were able to produce the fantastic complex we call the cell, or even more rudimentary living organisms. A statement such as this is tantamount to saying that the possibility of spontaneously forming steel particles from iron ore and coal at high temperature could have led to the construction of the Eiffel Tower through a series of happy coincidences that assembled the materials in proper order. Even then, this comparison is very weak, for the actual structural complexity of an elementary living organism is much more complex than the structure of the Eiffel Tower, considered in 1889 to be a triumph of metal construction.
Those who ardently defend the role of chance base their opinions on experiments of this kind, which claim to reproduce the possible origins of life. They repeat the views of Miller, who in 1955 induced the formation of complex chemical compounds; such as the amino acids present in cellular proteins, using electric sparks in an atmosphere of gas composed of steam, methane, ammonia and hydrogen. Needless to say, such experiments do not provide any explanation for the organization of the components; nor do we have any idea whether this favourably composed gas really existed in the earth's atmosphere two or three billion years ago. A theory cannot be built on unknown facts such as these. Even if a gas of this kind did exist in the earth's atmosphere; even if certain physical conditions did trigger high-powered electrical phenomena; even if complex organic chemical compounds had formed as a result of this fortunate combination of circumstances, there is nothing to prove that they could have induced the creation of living matter. The determining factor for this phenomenon remains unknown. Some researchers admit that there is an enigma in this. Others point to chance a convenient loophole that excuses them from acknowledging their ignorance. We shall come back later to the reasons why it is impossible to explain the phenomenon of life in terms such as these.
We must indeed turn to disciplines other than biochemistry to find the first clues to the problem, and in particular we must look toward palaeontology. Certain prehistoric animals and vegetals were not totally destroyed after their death. Their remains lay buried in sedimentary terranes, protected thereby from disintegration, and thus providing us with vestiges of these prehistoric life forms. The state in which the vestiges are found sometimes allows us ''to draw certain conclusions concerning the morphology and age of these once living beings [The material studied by Paleontology is limited to the bones and teeth]. It is in fact possible to gain an immediate idea of their age by establishing the date of the terranes. This can be done by various methods, in particular by radioactive measurements (radio chronology). For terranes that are geologically less ancient, carbon 14 tests are used, while strontium and rubidium tests are employed for older terranes. Having carried out these tests, experts can then determine the age of the specimens under investigation.
Tests such as these lead us to think that living beings existed in a unicellular state roughly one billion years ago [The earth is 4.5 billion years old]. Although it cannot be stated for sure, other forms may have existed before them. P: P. Grasse’, in his book entitled `Evolution du Vivant' [The Evolution of Living Organisms] [Published by Albin Michel, Paris, 1973], mentions the discovery of vestiges of much older organisms: for example, the existence of organized life forms roughly 3.2 billion years ago in the rock formations of the Transvaal. These forms could possibly represent tiny bacteria, smaller than 1 / 10,000 millimetres, as well as particles of amino acids. These organisms may have employed amino acids, or possibly proteins contained in the sea...Other microorganisms may also have been present in the sediments, such as cyanophilous algae containing chlorophyll. The latter is a basic agent in photosynthesis, a process by which complex organic compounds are formed from simple components through the effect of light. Fossilized vegetation resembling algae and filamentous bacteria have been found in more recent rock formations (2.3 billion years old) near the shores of Lake Superior in Canada. The bacteria and certain algae displayed an extremely simple structure, without the well known differentiated elements of the cells. Similar samples dating back roughly one billion years have been discovered in rock formations in Central Australia. This stage probably gave way to a period in which algae of a different kind displayed a genuine cell structure, with a nucleus and chromosomes containing molecules of deoxyribonucleic acid, D.N.A for short. Many facts about these algae remain unknown, however.
The pluricellular stage was to follow, but "in the animal kingdom, between uni and pluricellular forms, there was still a hiatus". Two basic notions must be mentioned immediately
a. The aquatic origins of primitive organisms;
b. The emergence of a growing complexity, passing from one form to another combined with the appearance of new organisms.
This growing complexity is ever present throughout evolution: We find similar fossilized vegetation at a much more `recent' period, 500 million years ago. We cannot be certain, of course, that today's bacteria are identical to those said to have appeared on earth as the first living organisms. They may have evolved since then, although bacteria such as Escherichia Coli have indeed remained the same for 250 million years.
Whatever the answer, the origins of life definitely appear to be aquatic. According to today's thinking, it is impossible to conceive of life without water. Any search for traces of life on other. planets begins with the question: Has water been present there? On the earth's surface, the combination of certain conditions including the presence of water was required for life to exist at all.
The complexity of living matter in those very first organisms is not likely to have been as great as it is in today's cells. Nevertheless, as P: P. Grasse’ points out: "In order for life to exist, there must be a production and exchange of energy. This is only physically possible within a system that is heterogeneous and complex. The established facts at the command of the biologist provide a reason for him to concede that the first living form was of necessity an organized entity". This leads Grasse’ to stress the important fact that today's bacteria, which appear to be the simplest living organisms, obviously attain a high degree of complexity. They are indeed composed of thousands of different molecules containing systems of catalysis that are themselves highly numerous, and which enable the bacteria to synthesize their own substance, to grow and to reproduce. The catalysis relies on enzymes, which act in infinitely small quantities, each enzyme performing its own specific function.
Like the amoeba, unicellular life forms are composed of differentiated elements. Their structure is amazingly complex, even though the cells are measured in units of 1 / 1,000 of a millimetre. Within the fundamental substance of unicellular forms, called cytoplasm, whose chemical structure is highly complex, there are numerous differentiated elements, the most important of which is the nucleus. This is composed of many parts, in particular the chromosomes containing the genes. These control every single aspect of the cell's functioning. They give orders through a system of information transfer, using transmitters and a system to receive the orders as they come in. The chemical vehicle supporting the genes has been clearly identified: It is deoxyribonucleic acid (D.N.A.), a molecule of complex structure. The `messenger' is a related molecule known as ribonucleic acid, R.N.A for short. Within the cell, it is this system that ensures the formation of new proteins from simpler chemical elements (synthesis of proteins).
It is difficult not to feel tremendous admiration for the molecular biologists that first discovered these extremely complex mechanisms systems so perfectly regulated to maintain life that the slightest malfunction leads to deformities or monstrous growths (cancer is a case in point) and ends in death. As far as I am concerned, however, the brilliant analysis of the way this system works (for each and every cell is a kind of computer comprised of innumerable interrelations) is just as amazing as the general conclusions cited above concerning the supposed resolution of unexplained facts on the origins of life. One very important question immediately springs to mind, based on the results of these investigations: How could 'a system as complex as this have been formed? Was it the work of chance, following a host of trials and errors? That seems most unlikely. What other logical theories are there? It is common knowledge that a computer will only function if it has been programmed, a fact that implies the existence of a programming intellect, that provides the information required to operate the system. That is the problem facing all thinking people who seek an explanation to such questions; people who refuse to accept mere words of groundless theories; people who will only acknowledge conclusions based on facts. Given the present state of knowledge, however, science has not provided any answer to this precise point.
The Diversity of Living Beings
There is tremendous diversity among living beings. From the most ancient times, human observers have noted this diversity and have taken great pains to analyse it in minute detail. Naturalists record the striking precision of certain primitive peoples in their ability to distinguish between the species of animals surrounding them. Having received no instruction from outside, these peoples have compiled inventories that are not far off the work of an expert.
The first distinction to be made between living beings is the separation of the animal and vegetable kingdoms. Although they share a common basic element the cell as well as numerous constituent substances, they are different in several ways. The vegetable kingdom is directly dependent on the earth for its nourishment. It also requires a much greater capacity for producing complex chemical compounds from simple bodies and light. The animal kingdom, on the other hand; depends on the vegetable kingdom for its nourishment (at least with regard to animals that have attained a certain degree of complexity), and carnivores depend on other species of animal.
Henceforth, we shall concentrate uniquely on the animal kingdom, which is extraordinarily varied and large. There may be as many as 1.5 million species living on our planet. The list has continued to grow, especially in recent decades, with the discoveries made in the marine world. Ever since the natural sciences gained stature and importance in the seventeenth century, format classifications have constantly appeared, each updated in turn as new data are discovered.
Aristotle drew a distinction between animals with red blood and those without, but no other studies of a serious nature were undertaken until the seventeenth century, when more interesting characteristics began to attract attention. For example: Some observers were struck by the question of respiration through the lungs or the branchiae (fish gills), the existence or absence of a vertebral skeleton (backbone), the anatomy of the heart (number of ventricles), or the existence of hair as opposed to feathers. ' In the classifications that were to follow, characteristics such as these remained distinctive of certain animal groups.
The distribution of distinguishing attributes opened the way for classification by group, with series of subdivisions. Thus the phyla [Plural of Phylum] characterise the broad basic divisions of the living beings presenting similar features, allowing us to put them in the same group. Each phylum can be divided into clearly defined classes; these are also determined by a certain number of specific characteristics. Similarly, each class contains several clearly differentiated orders, which nevertheless maintain the general features of their class and phylum. An order consists of various families, the families are composed of genera [Plural of genus], and the genera contain different species displaying both collective and specific characteristics. Classification is further complicated, however, by the existence of intermediary forms.
The first phylum of this classification is composed of unicellular forms, known as protozoans. It includes the most primitive beings, which very probably divided at some point in time, thus giving birth to pluricellular forms: This is the first example of evolution in the course of time.
The structure of these pluricellular forms (spongiae, cnidariae and ctenophores) became more complex as some acquired more specialized functions, without however constituting organs with clearly defined attributes. For example, some provided the covering of animals, others developed the ability to contract, or became sensitive to outside stimuli, and others acquired reproductory functions. The system grew more involved when a cavity appeared that served as a digestive tract (cnidariae and ctenophores) and the sensory organs made their appearance. This group did not as yet possess a head, however.
Embryological data have been of great value in establishing the various classifications in the animal kingdom. Thus an important stage in the growth of a structural complexity was reached with the early appearance during embryonic development of an extra germ layer. The number of layers thus grew from two to three, each layer ensuring the formation of clearly defined organs. Animals with three germ layers were in turn divided into 2 groups: those containing a single cavity (the digestive tract) and those with cavities that developed next to the digestive tract and which were responsible for the formation of tissues and various other organs. The broad divisions of the animal kingdom, here reduced to their most basic terms, already seem to suggest a methodical organization.
The latter guided, the birth of the various phyla, of which 20 emerged (very unevenly) into the following four groups
a. The unicellular forms, constituting a unique phylum;
b. The pluricellular beings containing two germ layers in the embryo [The external layer (ectodern) and the internal layer (endodern)], these gave birth to three phyla;
c. The pluricellular beings with three germ layers [The first two layers plus a third (mesodern) interposed between the two others] but containing only one cavity, these accounted for six phyla.
d. The group of animals with three germ layers and several cavities, constituting the other twelve phyla, two of which are particularly important: They are the arthropods which comprise the largest number of species in the animal kingdom, among which we find the insects and the vertebrates, the latter including fishes, reptiles, birds and mammals.
Nevertheless, the gaps in our knowledge of the transitions from one of these groups to another are very wide indeed. In the case of the insects, one of the most important groups, we know nothing whatsoever of their origins (P. P. Grasse) Likewise, there are no fossils left to indicate the beginnings of the various phyla. "Every explanation of the mechanism that governs the creative evolution of the basic organizational plans is weighed down with hypotheses. This statement should figure at the beginning of any book dealing with evolution. Since we have no firm documentary evidence; statements on the origins of the phyla can only be suppositions, opinions whose degree of feasibility we have no way of measuring." P. P. Grasse’s observation on the phyla should caution any statement on the origins of the major basic divisions. From this point of view, the determining causes of the phenomena in question are just as mysterious as the birth of the most rudimentary life forms.