The key component of the theory of evolution is natural selection. Define this p

Question

The key component of the theory of evolution is natural selection. Define this process. Why is it commonly known as “survival of the fittest”? What are examples of factors (selective pressures) that drive evolution of populations?

Be able to explain why the following statement is true: Natural Selection works on individuals while evolution works on populations over generations. Or to put it another way: Individuals do not evolve, populations do.

How can evolution explain the formation of complex structures such as the eye or the flagella motor?

Explanation / Answer

The struggle for existence means the competition between species to obtain food, living space and other needs of life. In the struggle, the predators having advantage would catch more prey and if the prey has an advantage could have better escaping options like camouflage or protection like that of porcupine. This is the central idea of Darwin’s theory of evolution. A key factor leading the struggle for existence is the suitable of organism to its environment to survive and reproduce. This is known as fitness. Some organisms adapt certain characters to improve their chance of survival. This can be explained as survival of the fittest which gives the idea that the organism that can fit more in an environment can survive longer and reproduce successfully.

Each trait is controlled by two or more alleles in a gene pool. The genetic variations in species are possible through mutation and gene shuffling. The changes in environment and genetical changes caused by mutations are few examples of selection pressures.

The process of natural selection is the source of evolutionary change. Small populations with less genetic variations become more or less common in population and it is simply by chance. Large populations with big genetic variation have the traits with high chances to become common in population. The random change in allele frequency is known as genetic drift which is operated by means of size selection.

In natural selection the biological traits have more or less chances to become common in population irrespective of the source of inheritance. This is known as sexual selection.

The individuals showing higher fitness near the center of the curve than the individuals at either end of the curve is known as the stabilizing selection. The population of lizards with the smallest and largest being easily preyed up on than the middle sized lizards is a kind of natural selection through stabilizing selection.

The individuals exhibit high fitness at one end of the curve than the individuals of the middle and at the other end of the curve. This is known as directional selection, a process of natural selection.

The individuals at the upper and lower ends of the curve exhibit the higher fitness than the individuals at the middle of the curve. This is known as disruptive selection, a process of natural selection.

For example, a change in distribution is caused due to stabilizing selection because of which a new beach color makes medium tan crabs the least visible to predators than dark or light colored crabs.

Individual birds with varying beak sizes have different chances of survival during draught. When the food sources are scarce the birds with the largest beaks were able to survive and the beak size plays an important role in the mating behavior resulting in average beak size in the population. The change in the beak size is based on the directional selection.

Theory of natural selection proposed by Darwin was questioned by the example of the evolution of eye. The eye’s ability to provide vision depends on the arrangement of its parts. Eye is the complex part with function as simplest light-sensitive spot. The selective advantage should be more to overcome the effects of genetic drift’s tendency and to eliminate beneficial mutations. Primitive eyes and light-sensing organs can be found in the animal kingdom and the evolutionary history of eyes was drawn out through comparative genetics. By these results, it can be known that the eyes must have arisen independently at least 30 times because of no availability of evolutionary pattern to explain the origin of eyes from a common ancestor.

The bacterial flagellum, a whip like cellular organelle used for movement through propulsion like a motor. The proteins that make up a flagellum are arranged into motor components. There is no evolutionary evidence available for organization and function of flagellum. Earlier flagella were simple than the sophisticated components of flagella found in later generations. The evolvement of flagellum might have involved the recombination of sophisticated parts that were evolved for other purposes earlier.

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