Question

Define evolution. How does it occur? Describe how fossils provide us evidences in support of evolution.

Answer 1

Evolution: Evolution is the process of generating new varieties by the accumulation of genetic differences in the pre-existing life forms or living organisms over a certain period.

Evolution occurs because of the following reasons-

a. Variations:

• The variations are the differences in the characteristics of the traits of individuals of the same species.
• The variations can be either hereditary or environmental.
• Hereditary variations are differences in the genetic makeup of individuals of the same species. The hereditary variations are passed on to the next generation.
• Environmental variations are differences in the outer look or physical appearance of the individuals due to environmental conditions. They arise due to the influence of the environment and these are non-inheritable.
• Sexual reproduction includes the formation of the gametes. These gametes are formed after the recombination or reshuffling of the genes of the parent. The reshuffling causes variations.
• Errors in the copying of the genes or DNA (Deoxyribonucleic acid): This creates variations in both sexually and asexually reproducing organisms.

b. Theory of natural selection:

• The theory of natural selection explains how the accumulation of the variations (genetic differences) in the populations occur that lead to the generation of the new varieties.
• This theory proposed by Charles Darwin suggests that evolution occurs due to selection by the nature. Genetic differences naturally exist in the population of the same species. Nature selects the differences that favor reproduction and survival in an environment.
• Some individuals of the same species carry some variations within the genes that make them survive in a better way than others. These favorable variations help with the struggle for survival and reproduction.
• Nature selects the organisms that are reproductively fit for survival over the other individuals.
• These favorable variations are then passed on to the next generations. Over a period, the variations become fixed or get accumulated in the population.
• This way, the new variety is created having those favorable variations.

c. The other factors that lead to evolution are:

• Genetic drift: Genetic drift is the alteration in the frequencies of the genes because of a chance event.
• Geographical isolation: Geographical isolation is the prevention of the gene flow among the group of population separated by a geographical barrier such as a mountain or a river.

Example of evolution: resistance against insecticide in insects

• The spraying of the insecticide on a population of insects does not kill all the insects.
• Some of the insects have variations in their genes that help them survive. The variations help them break down insecticide or fight against this.
• The insects carrying favorable variations survive and reproduce to increase their number. The favorable variations keep passing on to the next generations.
• These insects show resistance against insecticide, so, unless the amount of the insecticide is increased or the insecticide is changed, they keep growing due to the resistance in them.
• When a new insecticide is used, the insects can develop resistance again by the same process, that is, accumulation of the favorable variations.

Fossils: Fossils are the preserved remains of organisms like plants and animals that existed on the earth a long time ago but got buried or extinct.

Evidence of evolution:

• The fossils help in tracing the particular time when the organism was living. For example, the depth at which the fossil is found is related to the period during which the fossil (organism) lived.
• The fossils provide the order of evolution of different species over time.
• Example: Archeopteryx is an example of a fossil that has features of both birds (have feathers) and reptiles (have a long tail). This fossil represents an interlink between birds and reptiles. This concludes that the birds have evolved from reptiles.