The Path to the Chromosome Theory of Heredity :: History Science Biology Essays

The Path to the Chromosome Theory of Heredity The notion of the chromosome conjecture of heredity is actually important to the understanding of evolution and genetics. There were many ideas, some correct and others not, which influenced the revolutionary discovery of chromosomal heredity. The main st unitys in the path to the chromosomal theory are the pangenesis hypothesis, the germ-plasm theory, and Mendels Laws.PangenesisLamarck expressed the idea that by simply using or not using certain organs they may be essential or atrophied and their offspring can then inherit these acquired characteristics. (Milner p. 375, 1993) It should be noted that this theory was not widely accepted largely due to the fact that the French word that Lamarck used in the sense of must was translated as wants to, which makes it sound as though the organism decides to change its body. Furthermore, Lamarck provided no mechanism by which this could take place. (www.ridgenet.net/do_while/sage/v1i8f.htm ) Darwin was the one to give a mechanism for Lamarcks idea. This mechanism is known as pangenesis.Darwins ideas of evolution were well founded in the offset printing however, as his theory progressed he reverted to Lamarckian thought to explain his observations. To begin his theory he started with the observations that there is variation in offspring. He wrote, no one supposes that all the individuals of the same species inhabiting the same confined locality, are cast of the same moldI am convinced that the most experienced naturalist would be surprised at the number of the cases of variabilityas I have collected (Chapter 2 of Origin of Species). He sees that there is a struggle for foundation saying, as more individuals are produced than can possibly survive, there must in every case be a struggle for existence (Chapter 3 of Origin of Species). Finally, Darwin recognized that there is a survival of the fittest in that the organisms with the best variations for the continuan ce of the species live and those with variations that are not as useful to the continuation of the species hold out (Chapter 4 of Origin of Species). Darwin begins to diverge into Lamarckian thought at this point. Darwin wrote that, slightly different changes in the conditions of life add to the vigor and fertility of all perfect beingsthe crossing of forms which have been exposed to slightly different conditions of life or which have varied, favours the size, vigor, and fertility of their offspring (Chapter 9 of Origin of Species).