Notes On Evolutionary Relationships I - CBSE Class 10 Science
All the life on Earth has descended from a common ancestor. Evolution: It is the sequence of gradual changes over millions of years in which new species are produced. Charles Robert Darwin was an English naturalist who observed various species of life on the earth and put forward the idea of “evolution of species by natural selection.” He said that a species inherits its characters from its ancestors. Variations: These are the differences among individuals of a species caused by genetic and environmental factors. Mutation: It is the change in the sequence of the nitrogen base pairs in DNA. e.g. A mutation in the gene for green colouration in green beetles leads to offspring with brown colouration. Gene flow: It is the transfer of genes from one population to another due to migration. Breeding between the brown and green beetles introduces new gene combinations into the population. Natural selection: It explains that organisms that are physiologically or behaviourally better adapted for the environment are selected. Selected organisms can survive and reproduce.  Genetic drift: It is the genetic variation in small populations caused by a specific environmental factor.  Species: It can be defined as a group of individuals of the same kind that can interbreed and produce fertile progeny. Speciation: It is an event that splits a population into two independent species which cannot reproduce among them.          • Process of speciation-Genetic drift: It occurs due to changes in the frequencies of particular genes by chance alone. e.g. If a hurricane strikes the mainland, and bananas with beetle eggs on them are washed away to an island. This is called a genetic drift.          • Process of speciation - natural selection: These are the variations caused in individuals due to natural selection which lead to the formation of a new species. e.g. If the ecological conditions are slightly different on the island as compared to the mainland, it leads to a change in the morphology and food preferences in the organisms over the course of generations.          • Process of speciation - splitting of population: A population splits into different sub-populations due to geographical isolation that leads to the formation of a new species.

#### Summary

All the life on Earth has descended from a common ancestor. Evolution: It is the sequence of gradual changes over millions of years in which new species are produced. Charles Robert Darwin was an English naturalist who observed various species of life on the earth and put forward the idea of “evolution of species by natural selection.” He said that a species inherits its characters from its ancestors. Variations: These are the differences among individuals of a species caused by genetic and environmental factors. Mutation: It is the change in the sequence of the nitrogen base pairs in DNA. e.g. A mutation in the gene for green colouration in green beetles leads to offspring with brown colouration. Gene flow: It is the transfer of genes from one population to another due to migration. Breeding between the brown and green beetles introduces new gene combinations into the population. Natural selection: It explains that organisms that are physiologically or behaviourally better adapted for the environment are selected. Selected organisms can survive and reproduce.  Genetic drift: It is the genetic variation in small populations caused by a specific environmental factor.  Species: It can be defined as a group of individuals of the same kind that can interbreed and produce fertile progeny. Speciation: It is an event that splits a population into two independent species which cannot reproduce among them.          • Process of speciation-Genetic drift: It occurs due to changes in the frequencies of particular genes by chance alone. e.g. If a hurricane strikes the mainland, and bananas with beetle eggs on them are washed away to an island. This is called a genetic drift.          • Process of speciation - natural selection: These are the variations caused in individuals due to natural selection which lead to the formation of a new species. e.g. If the ecological conditions are slightly different on the island as compared to the mainland, it leads to a change in the morphology and food preferences in the organisms over the course of generations.          • Process of speciation - splitting of population: A population splits into different sub-populations due to geographical isolation that leads to the formation of a new species.

#### Activities

Activity 1 Newscientist.com has created an animation template which allows the user to know basic concepts of 'Evolution'. It deciphers important steps in evolution in the form of labels. These labels when clicked provide us necessary information to support the concept of 'Evolution'. Go to Activity Activity 2 Sciencenetlinks.com has created a game named 'Evolution'. The undercurrent of the game is to make the student more knowledgeable about the concept of 'Industrial Melanism'. The game is based on pepper moth and birds which feed on the former.   Go to Activity Activity 3 Mnh.si.edu has compiled an interactive session based on the concept' Evolution of Mammals'.It has a time liner on which we have to scroll upon the age. Based on the age selected, evolutionary changes that occurred during that period of time are listed. As per the period selected, mammal of that period is spotlighted. By just clicking on the options given, we can know about gradual evolutionary changes underwent by that mammal. Go to Activity

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