UNIT TWO : ORIGIN AND EVOLUTION OF LIFE
Class : 11
Structural and anatomical evidences
The types of organs like homologous organs, analogous organ and vestigial organs provide the evidences about structure.
Homologous organ : The organs, which are similar in structures and origin, called homologous organ. For e.g. human hand, Birds wing, bats wing, Horse's front foot are homologous organ.
Analogous Organ : The organs, which are not similar in structure and origin but function is same are called analogous organ. For e.g. Bird's wing and insect's wing, Fishes eye and mollusk's eye The analogous organs are developed due to similar habitat in evolutionary process.
Vestigial Organ : The useless and reduced organ are called vestigial organs are called vestigial organ. In human body, there are about 200 types of vestigial organ. For eg. Nictitating membrane, Vermiform appendix, Canine teeth, Caudal Vertebrae, Some snakes have vestige of limbs, Fishes lived in dark caves have reduced eyes.
Anatomical Evidences
The arrangement of different types of system like blood vessels, alimentary canal, skeletal system, excretory system etc is similar in vertebrates. Thus, the anatomy suggests in favor of organic evolution showing that the anatomical similarities become more and more complex progressively as one proceeds from lower animals to higher animals. All the varieties of animals have inherited the anatomical similarities from a common ancestor.
Paleontological Evidences
The paleontology deals with the study of fossils thus pale ontological evidences are the evidences of evolution from the fossil record suggesting that the evolution occur from simple form to the complex form.
a) Archaeopteryx
The most favorable evidence, which prove pale ontological evidence, is a kind of fossil bird named Archaeopteryx. This provides connecting link between reptiles and birds suggesting that the birds might have been evolved from reptiles. It represented the characteristics of both a bird and the reptile. It possessed following characters
- It had a beak like a bird but the beak contained teeth like reptiles.
- Its forelimbs were modified into wings like birds but claws on its wing like reptiles.
- It had feathers like birds but also had scales like reptiles. It had feathery tail like birds but had vertebrae like reptiles. Therefore, it is proved that the birds were evolved from reptiles and therefore the birds are called glorified reptiles.
b) Horse's Phylogeny
The evolutionary history of horse is termed as horse's phylogeny. The first horse (Eohippus) was small. The food had four toes. The time passed on and the modern horse is evolved named Equus having one toe and the size is large and high. The major modifications occur in the course of evolution of modern horse are
Increase in the body size. Increase of length and mobility of neck. Reduction in the number of toes from four to one. Specialization of teeth for grinding grass. Fusion of metatarsals and metacarpals.
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Biology