Theories of evolution: We all know that theory of evolution is given by Darwin, but before him there were many other scientists who have first work on the idea and gave different explanations on this theory.
Anaximander: He first explained about evolution in book called ”On nature” where he claimed that life started in water bodies then slowly spread to other drier areas.
Xenophanes: He explained different theories of evolution with the study of fossil.
Aristotle: He was the other great scientist who gave the idea of evolution with the study of marine animals and hence developed an epigenetic model of evolution.
John Ray: He also gave the idea of evolution through his book named, “Historia Plantarum”.
Carolus Linnaeus: He was the first one who gave systematic classification of species and he also gave concept on evolution but his ideas and explanation on evolution was not that clear with any strong evidences.
Comte de Buffon: He also gave the idea on evolution keeping environment as the direct medium for the changes that took place rather than anything else.
Pierre- Louis Moreau de Maupertuis: He gave the another theory where he explained that any changes that occurred with time was due to the chance only and in a book he also gave emphasis on the fact that strong and well adapted animals can have more offspring than that of weak animals.
George Cuvier: He was one of the great biologists who made several researches and contribution in the field of biology but he didn’t believe in the process of evolution and hence concluded that organism exists as a whole and any modification can cease their survival.
Lamarckism: His theories and concept for evolution was appreciated worldwide. He explained to the world that life started in a very simple form but slowly moved to the complex form. His theories are: 1. Use and disuse of organ: According to this theory, more we use any organ more it gets developed and less is the use, less will be it development. The most famous example includes neck of giraffe. It used its neck to reach the branches of the tree but could reach their due to short neck but slowly their neck developed and became longer than before so that they can reach high branches of trees. This theory failed because he explained the mechanism but couldn’t give the appropriate reason behind this. 2 Inheritance of acquires character: According to this theory, the character that is acquired by any organism is passed to the offspring. In case of neck of giraffe, if the parents are born with short neck but their neck is modified and developed large due to instant use then this character is transferred to the offspring. But this theory is also disapproved after the discovery of laws of heredity.
These are some of the theories of evolution before that of Darwinism theory. He explained his ideas, observations with most appropriate examples and explanation in book named origin of life. According to his theory, organism is produced in large number and all have equal chances of survival called overproduction. Among the thousands of offspring only some survive whereas others die. It is because only those who are fit for the survival survives and other dies called survival of the fittest. In the next theory he explained natural selection where nature selects only those organisms that are fit for the survival and possess necessary characters. Likewise, variation on the other hand serves as the advantages for every individual to survive in the population. This way Darwin gave different theories on evolution that is accepted and approved by everyone. Though there were some doubts in his theories but where soon cleared by Neo- Darwinism; scientist who worked on Darwin theory and cleared all the hazy concepts.
There are many theories on origin of life that have explained on how life began on the earth.
1. Special creation by god: This theory is not accepted because it focuses on the creation of this world under a supernatural power.
2. Theory of abiogenesis: According to this theory, life is created from non-living substance. This theory is supported by Aristotle and Von Helmont.
3. Theory of panspermia: This theory was given by Richter that tells that life is originated from other planet in the form of spores.
4. Theory of catastrophism: According to this theory, life was already there on the earth.
5. Theory of biogenesis: This theory was supported by different scientist and they have given different experiments to prove this theory. According to this theory, life came from preexisting form of life on the earth.
6. Theory of biochemical origin of life: According to this theory, life on the earth is the slow and gradual process that is originated when the temperature, atmosphere and environment on the earth became suitable that supported it. This concept is explained by Miller and Urey in the artificial way using ammonia, hydrogen, methane and water and electric spark in closed vehicle that help in origin of life.
7. Chemogeny: According to this theory, first simple compounds were formed, then organic compound were formed from the simple one and then complex were formed from organic ones. Then coacervates were formed, after the formation of coacervates, microspheres came that directed in the formation of primitive life, then autotrophs and finally the eukaryotes.
This way life on the earth was generated from simple to complex form that involves slow process with chemical changes taking place.
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