The universe is a system made up of the stars, planets and the space surrounding them. The earth is the one of the planets in the universe.
Plants, animals and other organisms like man, inhabit the earth. For many centuries man has witnessed and appreciated changes, which occur in nature and within his immediate surroundings. For example many thousands of years ago the Sahara desert was not there, instead the entire area was covered with a thick forest. Due to changes in weather the forest gradually disappeared and gave way to present desert. All this gives us the concept about organic evolution.
Evolution is the gradual development of organisms from simple form to more complex forms over a long duration of time. Evolution is marked by emergence of new species from pre-existing species and the disappearance of some species. The species that disappear are said to become extinct.
Key terms used in organic evolution
  • Carbon dating: This is a method of estimating the ages of dead materials of biological origin.
  • Natural Selection: This is selective force occurring in nature, which is responsible for eliminating the unfavourable traits to retain only favourable traits in the population.
  • Specie: These are organisms, which have ability to interbreed freely to produce fertile off springs.
  • Fossils: These are the remains of organisms that lived in the past, preserved naturally in rocks, peat or ice.
Importance of Studying Evolution
  1. It helps to understand the biological forces that cause organisms to develop from simple to more complex organisms to the extent of new
    species emerging
  2. It helps to know how different organisms relate


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