Question

Discuss the role of chance and direction in evolution and in determining the phenotype of a population

Answer 1

Evolution from prokaryotes to humans has occured because of the gradual changes and selection . It took millions of years for these changes to accumulate. There was no preplanned direction for evolution of humans. We have evolved by chance.

Raw material for evolution are variations. New variations are acquired through mutations. All mutations which occur naturally are random. Mutations are due to errors in copying of the DNA. Normally the DNA wrrors are rectified by varions repair enzymes present. But rarely they remain unrectified. Such errors in DNA will cause changes in phenotype which we call mutations. These mutations are random and bring random changes in the organism. So the phenotype or the trait has developed because of the mutations which are random. So it is by chance a variation occurs.

But the selection of variation is based on advantage and it is directional. If the variant is having advantage in the survival, such a variation is selected by nature. Based on the survival advantage the trait gets selected and establishes in the population. So the direction of selectrion is based on the advantage the variation gives to the population.

For example, giraffe did not get its long neck because it wanted reach to the tall trees. A mutation leading to sligtly longer neck has occurred by chance. But giraffe with such mutation had advantage over the others in reaching to tall plants. So such giraffe survived more and produced more offspring leading to incease in the number of such giraffe.

The selection process is continuous and directional as it selects advatageous phentypes. The neck became longer and longer over time to reach the present day evolution because of continuous process of selection of more and more longer neck. The process of evolution does not stop. It is a continuous process. Where the evolution leads to is not predictable as mutations occur by chance.