an essay on evolution of life
Answers
If the definition of evolution is changing in time, then the opposite of evolution is, clearly, not changing in time, or “stasis,” which means to stay the some in time. Things either change in time, or they don’t change in time. Those are the two opposites that must be considered when discussing evolution. Has the distribution of life on Earth change in time, or not change in time? If it’s change in time, then evolution is a fact; if it has not changed in time, then evolution is an error. So all we have to do is identify what has occurred in the past, in order to determine whether or not life has change over time. There is another question one could ask, “How in time did life come to be on the Earth?” One answer could be what science provides, according to certain rules that science choose to follow. Another answer could be God put life here. However, this is a statement that cannot be proven or disproved according to the rules of science, and it therefore is not a scientifically valid statement. Science is agnostic on God; it takes no position on God. If we chose science and God (which many people do), then one rephrases the question slightly: How, according to the rules of nature, did God create life on Earth? This is really the same as “how, according to the rules of nature, did life appear on Earth?” which is the question every evolutionary scientist is trying to answer. Whether one believe in God or not, the results, when conducted scientifically, should come out the same. The idea of evolution is one of the truly great ideas humankind has ever expressed.
Answer:
The word evolution, arising from the Latin word evolvere (to unroll) means the development of something by natural processes. Thus, we may talk of the evolution of the Earth, of the evolution of Man or of the evolution of a political dogma. When we talk of the Evolution Theory or about Organic Evolution we mean the evolution of life on this Earth, the greatest exponent of which idea was Charles Darwin.
If there can be a story based on facts there can be none more interesting than, that of the evolution of life on our Earth. The ideas of Evolution once began as poetic dreams, then as whispered theories, finally condensing into the bold assertions of Charles Darwin. Since then, evidences have piled up to such an extent that Evolution is no longer a mere theory but an established fact.
In talking about the evolution of life we begin from the beginning. Astronomers and geologists have concluded that this Earth first evolved out of celestial bodies as a fiery spinning ball of extremely hot gases. Gradually, through hundreds of millions of years, the gases cooled down and a solid core was formed.
An atmosphere of air (possibly somewhat different in composition from what it is today) formed a covering round it and the hot steam poured down as water forming the first seas and lagoons that were rather shallow. Life first began on this shallow water when it cooled down a bit. How did it begin? We have not yet got the answer but, perhaps, someday we shall. In all probabilities its origin was merely accidental and was possible only in the peculiar conditions of that time.
Still there are some scientists who believe that life originated outside our Earth and then it got transferred here. Whatever may be the cause of its origin, life began on this water by the formation of a speck of that mysterious substance— protoplasm. But, possibly, before the appearance of protoplasm there was a long history of natural synthesis of the most interesting organic substance protein, which is the basis of all living matter.
Proteins are formed of a number of common elements—C, H, O and N. But, protein molecules are very complicated and very large. As compared to the molecular weight 18 of water, that of insulin, a very simple protein and the only protein whose constitution is known (the structure was first established by Sanger in 1958 for which he was awarded the Nobel Prize), is about 5,000 while most protein molecules weight over 100,000 and some are known weighing about 10,000,000.These complex molecules are formed of simpler amino acid molecules which have the peculiar characteristic of having both acidic (CO.OH) and basic (NH.H) Parts so that the acid part of one molecule can unite with the basic part of another and, thus, a number of amino acid molecules may form what is known as a peptide chain (Fig. 792).
These chains turn and twist to form the complex protein molecules (Fig. 793). The atmosphere on our very primitive Earth had not been the same through the ages. About 3500 million years ago, when ‘life’ was possibly being evolved, it was much warmer there was no free oxygen in the air which, on the other hand, was possibly composed of free hydrogen, ammonia, methane and water vapour. It has been shown by Miller and Urey in 1955 that such a mixture of gases in a closed chamber when subjected to electric discharges gives rise to many of the known amino acids by artificial synthesis.
Such synthesis of amino acids might have taken place naturally in those days as result of atmospheric electric discharges or natural radiation. As this type of synthesis was possibly only in the atmosphere prevalent at that time, one may suppose that the origin of ‘life’ was possible only in those days. At least 21 types of amino acids are well-known today and they may combine in endless ways forming hundreds of protein types. Some of the proteins, like the egg albumin, have been obtained in crystalline forms.
We are now aware of a very interesting group of substances—the Viruses which are somewhat intermediate between the living and the non-living. The virus substances had been known since their discovery by Ivanovsky in 1892 as peculiar things which cause dreadful epidemic diseases in plants (e.g., tobacco mosaic virus) as well as animals (chicken-pox, smallpox, measles, influenza, poliomyelitis, rabies, etc.). The infective principles were known but they were not visible under the microscope and they could not be assigned to any type of living beings.
In 1953 Stanley obtained tobacco mosaic virus in the form of crystals which could infect other tobacco plants. Further researches have shown that these virus particles are nucleoproteins, i.e., compounds of nucleic acid and some protein. Each virus particle has a central core of ribonucleic acid (RNA) or, sometimes, deoxyribonucleic acid (DNA) and is encased by proteins.
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