Darwinism theory and its criticism

Darwin proposed the theory of natural selection after travelling all around the world and observed different species in the same area.

1. SEMINAR Topic: Darwin’s theory of evolution and its criticism Submitted by, maria manoj

2. Introduction Darwinism is a theory of biological evolution developed by Charles Darwin and others It states that all species of organisms arise and develop through the natural selection of small, inherited variations that increase the individual’s ability to compete, survive, and reproduce. Also called Darwinism theory. In 1831, he Ships on a trip around the world abroad In HMS beagle.

3. During his travels, Darwin made numerous observations and collected evidence that lead him to propose a revolutionary hypothesis about the way life changes over time.

4. Darwin saw far more diversity during his travels than he saw in his native country

5. Patterns of diversity Darwin was intrigued by the fact that so many plants and animals seems remarkably well suited to whatever environment they inhabited. He was also impressed by the ways in which organisms survived and produced offspring. He was also puzzled by where different species lived and did not live. Preserved remains of ancient organisms. Some looked like organisms that were still alive. Others looked completely unlike any creature he had ever seen. Darwin wondered, why had so many species disappeared, and how were they related to living species.

6. Galapagos islands Of all the beagles ports of call, the one that influenced Darwin the most was a group of islands off the coast of south America called the Galapagos islands. Although they were close together they all had different climates and differences between the species.

7. Observations Darwin observed that the characteristics of many animals and plants varied noticeably among the different islands of the Galapagos. Darwin began to wonder if animals living on different islands had once been members of the same species.  

8. Origin of species by theory of natural selection Over production or enormous fertility; living organisms have an innate capacity to produce more individuals to ensure continuity of the race . For example, oyster- 60-80 million eggs per year. rabbit - 4 litters per year salmon produces -28,000,000 eggs in a season.

9. 2. Struggle for existence: Organisms multiply in a geometric ratio, while the food supply increases in an arithmetic ratio. This leads to intense competition between organisms to ensure living to obtain maximum amount of food and shelter. Struggle exists at three levels: Intraspecific struggle is the competition among individuals of the same species or closely related forms. This type of struggle is very severe as the need of the population is the same. Interspecific struggle is the struggle between organisms of different species living together. Individuals of one species compete with other species for similar requirements. Struggle with the environment means the various hazards of the nature like extreme heat or cold, excess moisture or drought, storms, earthquakes, volcanoes eruptions, etc. also affect the survival of various organisms .

10. Variations among organisms Differences that exist among organisms are called variations. Variations may be harmful, neutral or useful. Variations that are passed on from generation to generation are called heritable variations and these form the raw material for evolution. These variations arise due to changes in the genes or the chromosomes. 4. Survival of the fittest: During the struggle for existence, the individuals that exhibit variations beneficial in facing the environment will survive, while those that cannot face the hardship will be eliminated. Those organisms best able to survive and reproduce will leave more offspring than those unsuccessful individuals. This is referred to as survival of the fittest.

11. According to Darwin, the giraffe exhibited variations in the length of the neck and legs. When the grass on the ground became scarce, giraffes with long necks and legs had an advantage over those with shorter neck and legs, as they could feed on the tall trees. So these forms survived and reproduced and became abundant. Over a period of time, giraffes with short necks starved and became extinct.

12. Origin of species: As a result of struggle for existence , individuals that are better adapted, survived and became abundant. Slowly over a period of time, this group, which was remarkably different from the original population ,process continues to give rise to new species. Members of this group may possess variations that may be beneficial to them in another environment. T wo or more species may arise from a single ancestral species. Over many generations, unequal reproduction among individuals with different genetic traits changes the overall genetic composition of the population. This is evolution by natural selection. This mechanism can cause a population to change so much, that it becomes a new species. This is known as speciation.

13. Criticism of Darwinism: The following points have been raised against the theory of natural selection: Darwin was unable to explain the mechanism of inheritance of characters. Darwin proposed the theory of pangenesis to explain this phenomenon. He said that every cell or organ produces minute hereditary particles called pangene or gemmules . These were carried through the blood and deposited in the gametes. This theory was not accepted. According to natural selection, only useful organs are favored by natural selection. The existence of vestigial organs in organisms could not be explained. In some species of deer, the antlers develop beyond the stage of usefulness. These structures are of no functional significance to the animal. +

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