Evolution Class 12 Notes

What is Evolution?

Evolution is the study of the different forms of life, its characteristics and the changes over several generations. It is the scientific theory used by biologists to study the genetic variation in a population.

There are many theories about how life originated on the planet earth. The theory of evolution is based on the idea that all species are correlated and progressively varies with time.

Darwin’s Theory of Evolution

Charles Robert Darwin, an English naturalist, geologist, and biologist, is well known for his theory of evolution and the process of natural selection. He gave the theory of evolution, which is known as ‘Darwin’s theory of natural selection’ and also published a book, on “Origin of Species by Natural Selection”.

According to Darwin’s Theory, the main features of this theory are as follows,

  • All organisms reproduce and multiply enormously.
  • No two individuals are alike. They are different from each other either in their size, shape, behavior, etc.
  • Some traits are consistently passed on from their parent to the offspring.
  • The rate of reproduction varies in all living species. Some reproduce more and some minimum.

A Brief Account of Evolution

According to the several theories of Evolution:

  • The first cellular forms of life appeared on earth was about 2000 million years ago.
  • Later single-celled organisms, multicellular forms, and invertebrates were formed and became active.
  • Jawless fish evolved and different organisms started to invade from water to land. Later, amphibians, reptiles some of them to viviparous mammals came into existence.
  • About 23.03 to 5.333 million years ago, evolved primates that resembled to toady’s gorillas and chimpanzees. During ice age between 75,000-10,000 years ago, modern Homo sapiens arose.

Few Important Questions

  • Write a brief account of Evolution?
  • List out the 5 mechanisms of evolution?
  • What is Charles Darwin’s theory of evolution?
  • What Is Adaptive Radiation? Explain with examples.

Learn more about evolution and its theories from the topics given below:

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