Question

Explain the theory of evolution and mention the proof supporting it.

Answer 1

There are various theories of evolution but the most acceptable one is the theory of ‘Gradual development of living organisms’. According to this theory, the first living material which is the protoplasm was formed in the ocean. Gradual changes resulted in the formation of unicellular organisms and further developments resulted in the formation of larger and more complex organisms. However, these changes did not occur overnight, they were slow and gradual changes that took almost 300 crore years. These changes and developments are often referred to as evolution and are the prime cause of diversity of plants and organisms which we see on Earth today. There are various evidence that supports evolution:

1. Morphological evidence: Similarity in morphological features of animals and plants is evidence that they have evolved from common ancestors.
   For example: In animals similarities like structure of mouth, position of eyes, structure of nostrils and in plants, similarities in characters like leaf shape, leaf venation, leaf petiole represent common ancestry.
2. Anatomical evidence: Organs of different animals are dissimilar in function but similar in structures of bones and bony joints shows that these animals may have common ancestors.
   For example, the human hand, cat’s foreleg, patagium of bat and flipper of a whale perform different functions, but their bones are similar in structure.
3. Vestigial organs as evidence: Underdeveloped useless organs in organisms are called vestigial organs. Such organs are useless in some organisms but these organs are useful in other organisms.
   For example, the appendix is useless in humans but functional in cattle. Ear pinna muscle is useless in humans but useful in monkeys.
4. Connecting links: Connecting links refers to plants and organisms which show characteristics related to two different groups.
   For example, Peripatus is considered a connecting link between annelida and arthropoda. It has characteristics like a segmented body, thin cuticle, and parapodia-like organs, which are similar to annelids. It also shows tracheal respiration and an open circulatory system which is similar to arthropods. Another example is duck billed platypus which is a connecting link between reptiles and mammals because it lays eggs like reptiles and has mammary glands like mammals.
5. Embryological evidence: Embryology is used as one of the evidences of evolution. Comparative study of embryos shows that there is a lot of similarity in them at the initial stages whereas this similarity decreases gradually. This similarity in the development of embryos represents a common origin of organisms.

Answer 2

1. According to the theory of evolution, the first living material (protoplasm) was formed in the ocean.
2. Unicellular organisms formed in the course of time.
3. Slow and gradual changes in unicellular organisms led to the formation of larger and more complex organisms.
4. Through evolution, plants and animals progressively developed from their ancestors that had different structural and functional organization.
5. The evidence supporting the theory of evolution includes morphological evidence, anatomical evidence, vestigial organs, and paleontological evidence.