CBSE Class 12 Biology Notes Chapter 7 Evolution

Evolution is a fundamental theory in biology that explains the diversification of life on Earth.

• It is the study of different forms of life, their characteristics, and how these change over generations.
• It is a scientific concept used by biologists to explore genetic diversity in a population.
• The theory of evolution focuses on how existing species change over time. 
• It proposes that all species are related and progressively vary with time.

CBSE Class 12 Biology Notes for Chapter 7 Evolution are given in the article below for easy preparation and understanding of the concepts involved.

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Class 12 Biology Chapter 7 Notes – Evolution

Darwin’s Theory of Evolution

• Every organism reproduces and multiplies immensely.
• No two individuals are alike, but they differ from one another in size, shape, behavior, and so on.
• Some characteristics are continuously passed down from parent to offspring.
• The rate of reproduction differs among all living organisms. Some reproduce more, some reproduce less.

Theory of Evolution

A Brief Account of Evolution

• The first cellular forms of life emerged on Earth around 2000 million years ago.
• Later, single-celled species, multicellular forms, and invertebrates developed and became active.
• Jawless fish evolved, and different organisms started to spread from the sea to the land. 
• Later, amphibians and reptiles appeared, including several viviparous mammals.
• Primates that resemble modern gorillas and chimpanzees emerged between 23.03 and 5.333 million years ago. 
• Modern Homo sapiens emerged during the ice age, which occurred between 75,000 and 10,000 years ago.

A Brief Account of Evolution

Evidence for Evolution

The following are the evidence of evolution

• Fossils: They are the non-degraded remains of living organisms found within rocks. 
  • The layer from which the fossil is collected determines its age. 
  • The fossils found deeper down are older than those found in the upper layers. 
  • They provide an understanding of the condition of the earth during that period. 
  • The study of fossils is known as paleontology, hence they are known as paleontological evidence.
• Comparative Anatomy: It shows shared ancestry among organisms, with evolution driven by natural selection or genetic drift.

Two types of comparative anatomy were observed:

• Homologous organs
• Analogous organs

• Embryonic Development: The embryos of many animals show comparable anatomy until a certain point of gestation.
  • Human embryos, for example, develop similarly to those of pigs, reptiles, and birds. 
  • They develop into their respective species as they grow.

Adaptive Radiation

• This process describes the evolution of diverse species from a common ancestor within a specific geographic region. 
• The new species then radiate outward, adapting to different environments, for example, Australian marsupials and Darwin's finches.
• Inherited traits that increase the ability of an organism to survive in a harsh environment (adaptation) lead to higher fitness and selection by natural selection.

Adaptive Radiation

Hardy-Weinberg Principle

• The Hardy-Weinberg principle establishes genetic equilibrium in a population.
• This principle states that allele frequencies remain constant across generations.
• This is referred to as genetic equilibrium with the sum of all allele frequencies equal to 1. 
• For example, in a diploid organism, the probability of inheriting two copies of allele A (frequency p) is simply p2.
• Five factors can affect this principle are:
  • Gene flow (movement of alleles between populations)
  • Genetic drift (random fluctuations in allele frequencies)
  • Genetic recombination (reshuffling of alleles during meiosis)
  • Mutation (changes in DNA)
  • Natural selection (favoring certain traits).

There are Some important List Of Top Biology Questions On Evolution Asked In CBSE CLASS XII