Explain the theory of evolution of life with the help of following evidence of organic evolution :
{a} Anatomical evidence {vestigial structures}
{b} Palaeontological evidences
Answers
ANATOMICAL EVIDENCES
Vestigial Organs: These are those organs which occur in reduced form and are useless to the possessor but are fully developed and functional in the related animals. These organs were necessary in the ancestral forms; bur are gradually disappearing in the present say forms due to change in their mode of life. EXAMPLES:
1 Tail bone(coccyx) in human beings.
2 Third eyelid in human beings(Nictitating membrane) is highly reduced and non-functional in all of us as the cornea is cleaned by the upper eyelid. But it is well developed and functional in frog, pigeon and cat.
3 Auricular muscles are present in pinna in mammals with these muscles mammals like rabbit, dog and cow move their pinna towards the source of sound. But in case of man these muscles are reduced and non-functional.
4 Caecum and vermiform appendix: vermiform appendix is the blind tube at the end of caecum found in some mammals. In herbivores. caecum and vermiform appendix are highly developed and helps in the digestion of cellulose. But in man it is reduced and non functional.
5 The snakes have evolved from lizard like reptiles having two pairs of limbs(functional). But due to change in their mode of life, they have lost the limbs but pythons and boas still retain the hind limbs.
PALEONTOLOGICAL EVIDENCES:
- Fossils of single celled prokaryotes or microfossils were found that were believed to be 3500 million year old. These were similar to those found living today.
- Fossilized remains of STROMALITES were found and provided information on the structure of early organisms. Simple bacteria existed in these structures were very similar to present day STROMALITES>
- Discovery of NANOBACTERIA were found in meteorite of mars.
In general, using fossil evidence from different rock layers it has been found that the more primitive cells and marine organisms are found in lower layers compared to the more complex and land dwelling organisms. It suggested that simple organisms precede complex organism.
a) Evidences from Comparative anatomy
b) Evidences from Paleontology
a) Evidences from Comparative anatomy/ Anatomical evidences {vestigial structures}
The organs which were functional in the ancestors but non-functional and reduced in the descendants are called vestigial organs. Presence of vestigial organs is the most convincing evidence in favor of organic evolution and also supports the concept of disuse proposed by Lamarack.
E.g. Hind limbs in python, hind limbs and pelvic girdle in whale , wings of flightless birds, vermiform appendix, coccyx, plica semilunaris, hair on the body, etc., in humans.
b) Evidences from Paleontology/Palaeontological evidences
Paleontology is the study of prehistoric life through fossils.Fossils are the remnants of plants or animals that were preserved in the layers of the earth and have been excavated from the soil.They are of various types like moulds, casts, petrifications, coprolites, actual remains of animals preserved in ice, etc. They support the idea that life has gradually evolved on the earth. The biologists and paleontologists have found the fossils of many transitional forms which link all the major groups of vertebrates.
E.g. Eusthenopteron between fishes and amphibians, Seymouria between amphibians and reptiles, Archaeopteryx between reptiles and birds, Cynognathus between reptiles and mammals etc.
[The age of fossil is calculated by using Carbon¹⁴, Uranium²³⁸ and Pottasium⁴⁰. Of these, as C¹⁴ is commonly used to determine the age of comparatively recent and this method is called Radio Carbon Dating method]