The following points highlight the five important evidences that prove the evolution of life on earth. The evidences are: 1. Miller-Urey Experiment 2. Palaeontological Evidences 3. Comparative Anatomy and Morphological Evidences 4. Biochemical Evidences 5. Bio-Geographical Evidences.
1. Miller-Urey Experiment:
Stanley Miller and Harold Urey performed the experiment in 1953.
They demonstrated clearly that ultraviolet radiations or electrical discharges or a combination of these can produce complex organic compounds from a mixture of CH4, NH3, H2O and H2 and the ratio of methane, ammonia and hydrogen was 2: 1: 2 in the experiment Electric discharge was created, in a closed flask containing CH4, NH3, H2 and water vapour at 800°C.
The conditions were set similar to those in the primitive atmosphere in the laboratory. After a week, they observed the presence of complex molecules like sugar, pigments, nitrogen bases, fats and amino acids in the flask.
They proved that the first non-cellular form of life was created about 3 million years ago (mya) and non-cellular bio-molecules exist in the form of RNA, DNA, protein and polysaccharides, etc.
2. Palaeontological Evidences:
It is the study of fossils. Rocks from sediment and cross-section of the earth’s crust depict the arrangement of these sediments one over the other, during a long history of earth.
Sediments of different aged rocks contain fossils of different life forms that lived and died during the formation of a particular segment.
A study of fossil in different sedimentary layers indicates the geological period in which they existed.
The study showed that the life forms varied overtime and certain life forms are restricted to certain geological time scale. Hence, new forms of life have evolved at different times in the history of earth.
3. Comparative Anatomy and Morphological Evidences:
These show the similarities and differences among the organisms of today and those existed years ago. These evidences come from the comparative study of external and internal structure.
These can be determined by the following types:
It is the relation among the organs of different groups of organisms, that show similarity in the basic structure and embryonic development, but have different functions. Homology in organs indicates common ancestry. It is based on divergent evolution. When due to different needs, some structures developed differently, the condition is called divergent evolution. This results in the formation of homologous organs.
Examples of homology are as follows:
(a) Forelimbs of animals like whales, bats and cheetah.
(b) Vertebrate’s heart and brains.
(c) Thorns and tendrils of Bougainvillea and Cucurbita.
It is a situation, exactly opposite to the homology. In analogy, the organs are functionally similar but anatomically different. Convergent evolution is the evolution where different structures develop similarly. This results in analogous organs.
Examples of analogy are as follows:
(i) Wings of butterfly and birds.
(ii) Eyes of Octopus and mammals.
(iii) Flippers of penguins and dolphins.
(iv) Sweet potato (root modification) and potato (stem modification).
4. Biochemical Evidences:
Among diverse organisms, the similarities in proteins and genes perform a common function. The metabolic processes in different organisms are also similar. This occurs due to common ancestry.
5. Bio-Geographical Evidences:
It suggests that the species restricted to a region, develop unique features. Also, species present in widely separated region show similarity of ancestry. Habitat isolation has probably restricted these organisms to a particular geography on the earth.