8. Darwinism.pptx
- 2. Charles Darwin (1809–1882) was born in Shrewsbury, in western England. Even as a boy, he had a consuming interest in nature. When he was not reading nature books, he was fishing, hunting, riding, and collecting insects. Darwin’s father, a physician, could see no future for his son as a naturalist and sent him to medical school in Edinburgh. But Charles found medicine boring and surgery before the days of anesthesia horrifying.
- 3. He quit medical school and enrolled at Cambridge University, intending to become a clergyman. (At that time, many scholars of science belonged to the clergy.) At Cambridge, Darwin became the protégé of John Henslow, a botany professor. Soon after Darwin graduated, Henslow recommended him to Captain Robert FitzRoy, who was readying the survey ship HMS Beagle for a voyage around the world. Darwin would pay his own way and serve as a conversation partner to the young captain. FitzRoy, who was himself an adept scientist, accepted Darwin because he was a skilled naturalist and they were of similar age and social class.
- 5. Darwin embarked from England on the Beagle in December 1831. The primary mission of the voyage was to chart stretches of the South American coast that were poorly known to Europeans. Darwin, however, spent most of his time on shore, observing and collecting thousands of plants and animals. He described features of organisms that made them well suited to such diverse environments as the humid jungles of Brazil, the expansive grasslands of Argentina, and the towering peaks of the Andes. He also noted that the plants and animals in temperate regions of South America more closely resembled species living in the South American tropics than species living in temperate regions of Europe. Furthermore, the fossils he found, though clearly different from living species, distinctly resembled the living organisms of South America.
- 6. Darwin also spent much time thinking about geology. Despite repeated bouts of seasickness, he read Lyell’s Principles of Geology during the voyage. He experienced geologic change firsthand when a violent earthquake shook the coast of Chile, and he observed afterward that rocks along the coast had been thrust upward by several meters. Finding fossils of ocean organisms high in the Andes, Darwin inferred that the rocks containing the fossils must have been raised there by many similar earthquakes. These observations reinforced what he had learned from Lyell: Physical evidence did not support the traditional view that Earth was only a few thousand years old.
- 7. Darwin’s interest in the species (or fossils) found in an area was further stimulated by the Beagle’s stop at the Galápagos, a group of volcanic islands located near the equator about 900 km west of South America (Figure 22.5). Darwin was fascinated by the unusual organisms there. The birds he collected included several kinds of mockingbirds. These mockingbirds, though similar to each other, seemed to be different species. Some were unique to individual islands, while others lived on two or more adjacent islands.
- 9. The animals on the Galápagos resembled species living on the South American mainland, most of the Galápagos species were not known from anywhere else in the world. Darwin hypothesized that the Galápagos had been colonized by organisms that had strayed from South America and then diversified, giving rise to new species on the various islands.
- 10. Charles Darwin‟s concept of natural selection was explained clearly and convincingly by him in his masterpiece - The Origin of Species‟ the 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 in 1859. Its essence is that the animal and the plant worlds came into existence by a process of dynamic descent.
- 11. Darwin‟s explanation of the way in which evolution occurs may be generalized as follows. The change in species by the survival of an organismal type exhibiting a natural variation that gives it an adaptive advantage in an environment, thus, leading to a new environmental equilibrium, is evolution by natural selection. Thus natural selection is a continuous process of trial and error on a gigantic scale, for all of living matter is involved.
- 12. It includes the following element. The universal occurrence of variation Over production (rapid multiplication) Struggle for existence (a) Intraspecific struggle (b) Interspecific struggle (c) Environmental struggle Survival of the fittest Inheritance of useful variations
- 13. The difference between individuals within a population of a species constitutes variations. Variations are the characteristic of every group of animals and plants and there are many ways in which organisms may differ. Due to the variations some individuals would be better adjusted towards the surroundings than the others. Adaptive modifications are caused through the struggle for existence.
- 14. According to Darwin, the variations are continuous and those which are helpful in the adaptations of an organism towards its surroundings would be passed on to the next generation, while the others disappear. This will lead to change in populations over successive generations in a process that Darwin called descent with modification. Ultimately, natural selection leads to greater adaptation of the population to its local environment; it is the only mechanism known for adaptive evolution.
- 16. 1. While natural selection theory explains survival of the fittest, it does not explain the arrival of the fittest. 2. Over-specialization of some organs like tusks of elephants, antlers of deer have developed so much that instead of providing usefulness to the possessor they often give hindrance to them. 3. Natural selection cannot account for degeneracy-to say an organ is no longer useful and, hence, disappears, is to state the effect and not the cause. 4. One of classical objections to natural selection is that new variations would be lost by “dilution” as the individuals possessing them bred with others without them. 5. Darwin indirectly accepted the Lamarckian idea of inheritance of acquired characters in the form of pangenesis hypothesis, which cannot be accepted in the light of present knowledge of genetics. Antlers of deer Tusks of elephants,
- 17. Neo-Darwinism is a modified form of Darwinism. The Neo-Darwinians like T.H. Huxley, Herbert Spencer, D.S. Jordan, Asa Gray, E. Haeckel and A. Wiesmann believed that natural selection has accounted everything that is involved in evolution. Certain Neo-Darwinians such as A. Wiesmann and his followers rejected Darwin‟s theory except its principal element of natural selection. These Neo-Darwinians, though distinguished between germplasm and somatoplasm of living organisms in their germplasm theory, yet they could not appreciate the role of mutations in evolution.
- 18. Neo-Darwinians thought that adaptations result from multiple forces and natural selections is only one of these many forces in contrast to Darwin‟s belief who held that adaptations result mainly by a single source, i.e., natural selection Neo-Darwinians also believed that characters are not inherited as such but there are character determiners, the determinants or biophores, which control only the development. The ultimate character would result out due to the interaction of the determiners, activity of the organism and the environment during development. Thus, Neo-Darwinism was incomplete and partly wrong because it lacked present understanding of genetics.