Medical brain notes 33

  THEORIES OF EVOLUTION   Introduction   Several opinions had been made available to explain the origin and existence of various forms of life. The existing living beings show characteristic resemblances in form and functions. There are evidences for succession of several types of living organisms occupying earth. Populations of animals and Plants tend to undergo predictable changes in their population intensities. An explanation to all these interesting natural happenings had been attempted through various modern theories of evolution. An initiation for such evolutionary thought process was well provided by Lamarck. This evolutionary theorizing culminates in the modern synthetic theory of evolution afforded by different fields in biology.   Lamarckism   Jean Baptiste de Lamarck (1744 - 1829) is well known for his theory of evolution. In 1809 he published his book titled ' Philosophie Zoologique '. This book contains his views on evolutionary mechanisms. Eventho...

  THEORIES OF EVOLUTION   Neo-lamarckism   Lamarck's 'theory of inhertitance' was further studied by a group of scientists. Their ideas supporting Lamarck's opinion collectively constitute neo-Lamarckism.   The neo-Lamarckians were of the opinion that 'adaptions' are universal in nature. An adaptation happens through causal relationship of structure, function and environment. Due to changes in the environment, habits and life style of organism gets altered. Thus gradually the organism acquires new structures. The newly obtained character gradually becomes an inheritable trait. This opinion and argument is a modified form of Lamarckism. These ideas stressed direct action of environment on organisms.   Support to neo-Lamarckian concept - Experiments   1. McDougall (1938) tried to prove that learning is an acquired character that can be inherited. He did his experiments on rats.   He deviced a 'T' shaped tank. The tank had two exits. One exit was well lig...

  THEORIES OF EVOLUTION   Darwinism   Darwinism comprises the natural selection concept as advanced by Charles Robert Darwin in 1859. His theory provided the correct idea to explain all processes and intricate mechanisms of evolution. The theory of natural selection is considered on par with Newton's law of gravitation and Einstein's theory of relativity. The monumental work of Darwin was titled as 'The Origin of species' (the original full title of the book was 'On the Origin of species by means of Natural Selection, or the Preservation of favoured Races in the struggle for life').   The book of Darwin convincingly demonstrates the fact of evolution. Further, it elaborates on the theory of natural selection as a convincing mechanism for providing evolutionary transformations.   Charles Darwin was born in Shrewsbury, England on February 12, 1809. While studying in college at England through his friendship with Professor J.S. Henslow, Darwin became familiar with ...

  Modern concept of Natural Selection (or) Modern synthetic theory of Evolution.   Modern development in biological fields such as Cell biology, Genetics and Populations genetics helped in the development of modern synthetic theory of evolution. It was caused due to contributions made by eminent scientists such as Th. Dobzhansky, S.Wright, H.J.Muller, J.S. Huxley, R.A.Fisher, Ernst Mayr, G.L.Stebbins and others.   The basic concept of modern synthetic theory was provided by Th. Dobzhansky in his book titled 'Genetics and the Origin of species' (1937) G.L.Stebbins in his book 'Process of organic evolution' (1971) suggests five basic processes essential for evolution. They are  gene mutations ,  chromosomal aberrations ,  genetic recombinations ,  natural selection  and  reproductive isolation . Contributions made by others provided additional factors such as  Hardy-Weinberg equilibrium ,  Genetic drift  and  Polymorphism . ...