Write short notes based upon the information known to you:

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1. Lamarckism:

1. Jean-Baptiste Lamarck proposed that morphological changes occur in living organisms due to ‘use or disuse of organs’. These ‘acquired characters’ are transferred from one to the next. This is called as theory of inheritance of acquired characters or Lamarckism.
2. He gave the example of a giraffe. The neck of giraffe has become too long due to browsing on leaves of tall plants by extending their neck for several generations.
3. Similarly, shoulders of the ironsmith have become very strong due to frequent hammering movements.
4. Wings of birds like ostrich and emu have become weak due to no use.
5. Development of organs due to specific activities or their degeneration due to no use at all was widely accepted but transfer of those characters from generation to generation was rejected.
6. It had been verified many times that modifications brought in us are not transferred to next generation and thereby Lamarck’s theory was disproved.

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2. Darwin’s theory of natural selection:

1. Charles Darwin had collected innumerable specimens of plants and animals and depending upon the observations of those specimens; he published the theory of natural selection which preaches the survival of fittest. For this purpose, Darwin had published a book titled ‘Origin of Species’.
2. All the organisms reproduce prolifically. They compete with each other in a life-threatening manner.
3. Only those organisms which show the modifications essential for winning the competition survive.
4. Besides this, natural selection also plays important role because nature selects only those organisms which are fit to live and the rest perish.
5. Sustaining and selected organisms can perform reproduction and thereby give rise to the new species with their own specific characters.Sustaining and selected organisms can perform reproduction and thereby give rise to the new species with their own specific characters.
6. Darwin’s theory of natural selection was a milestone and widely accepted for long duration. However, some objections were raised against the theory.

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3. Embryology:

1. Embryology deals with the study of development of an organism from an embryo.
2. Comparative study of embryonic developmental stages of various vertebrates shows that all embryos show extreme similarities during initial stages.
3. These similarities decrease gradually.
4. Similarities in initial stages indicate the common origin of all these animals.

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4. Evolution:

1. Progressive development of plants and animals from the ancestors having different structural and functional organization is called evolution. This is a very slow-going process.
2. Different theories about origin and evolution of life have been proposed till today of which theory of 'Gradual development of living organisms’ is accepted.
3. 3.5 billion years ago, life had been non-existent on the Earth.
4. At the beginning, there may have been only simple elements in the ocean on the Earth and simple type of organic and inorganic compounds may have been formed from those.
5. Complex compounds like proteins and nucleic acids may have formed over the long period from those simple compounds.
6. First primitive type of cells may have been formed from the mixture of different types of organic and inorganic compounds.
7. In due course of time, unicellular organisms were formed. Gradually, changes occurred in the unicellular organisms from which larger and more complex organisms were formed.
8. All those changes were slow and gradual. Duration of all these changes is almost 300 crore years

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5. Connecting link:

1. Some plants and animals show morphological characters by which they can be related to two different groups they are called as connecting links.
2. Different theories about origin and evolution of life have been proposed till today of which theory of 'Gradual development of living organisms’ is accepted.
3. In Peripatus, characters like segmented body, thin cuticle and parapodia like organs are present.
4. Similarly, these animals show tracheal respiration and open circulatory system similar to arthropods.
5. This indicates that peripatus is connecting link between Annelida and Arthropoda.
6. Similarly, duck billed Platypus lays eggs like reptiles but shows relationship with mammals too due to the presence of mammary glands and hair.
7. These examples indicate that mammals are evolved from reptiles and amphibians from fishes.

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