Evolution – Class 12 | Chapter – 7 | Biology Short Notes Series PDF

Evolution: Evolution is a process that results in heritable changes in population spread over many generations leading to diversity of organisms on earth. 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.

It refers to the process by which living organisms change over time through changes in the genome. Such evolutionary changes result from mutations that produce genomic variation, giving rise to individuals whose biological functions or physical traits are altered. Those individuals who are best at adapting to their surroundings leave behind more offspring than less well-adapted individuals. Thus, over successive generations (in some cases spanning millions of years), one species may evolve to take on divergent functions or physical characteristics or may even evolve into a different species.

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.

 

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By Team Learning Mantras