Briefly explain the meaning of the following statement The h

Briefly explain the meaning of the following statement \"The history of life on Earth is the product of descent with modification from shared ancestors.\" Give a short and clear explanation of any one piece of evidence supporting that statement.

Solution

21. (a) Ancestors of living organisms have undergone several modifications to give rise to the forms we actually see now. This is possible due to evolution and natural selection. However, the process has been very slow. The common ancestors of living organisms underwent gradual as well as slow changes in order to evolve. However, nature selected for only the best descendant that was fit to survive under the existing conditions(natural selection). The Theory of Evolution of Darwin clearly emphasises on Branching descent and natural selection. This process of evolutionary change first of all started in different cellular forms of life with varying degrees of metabolic capability. Some of the descendants of common ancestor are better equipped to survive in otherwise hostile environment. Nature selects for only the best adapted form out of several descendants of common ancestor. Nature selects for only the fit descendants and the rest perish. Fitness of organisms are based on characteristics which are inherited.

(b) The most important peice of evidence suggesting the same is the comparative study of DNA base sequence of these organisms. Organisms descended from a common ancestor have closely related DNA base sequences( Sequence of A,T,G and C). Such organisms are said to be phylogenetically related. On the other hand, oraganisms that have descended from different ancestors do not show similarity in DNA base sequences. Comparison of the DNA genetic sequences of organisms has revealed that organisms that are phylogenetically close have a higher degree of DNA sequence similarity than organisms that are phylogenetically distant. All this information is also helpful in creating a phylogenetic tree.