Evolution

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Organic evolution is the process of slow and gradual change in organisms over hundreds or thousands of years from simpler ancestors. It explains how the great variety of organisms on Earth developed f

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The pattern of evolution shows: (a) Unicellular organisms appeared first, followed by multicellular organisms, (b) More complex forms evolved from earlier simpler forms. This demonstrates increasing c

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Jean-Baptiste Lamarck, a French biologist, proposed this theory in 1809 in his book 'Philosophie Zoologique'. It is also known as the Theory of Use and Disuse or Lamarckism.

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(i) Tendency to grow - organisms increase size of body parts, (ii) Formation of new organs - new organs develop due to long-felt need, (iii) Effect of use or disuse - frequently used organs develop, u

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According to Lamarck, giraffe ancestors were goat-sized. When ground grass disappeared, they stretched their necks to reach tree leaves. This constant stretching over generations was inherited, gradua

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Vestigial organs are non-functional organs in present-day organisms that were functional in ancestors. Examples in humans: (i) Vermiform appendix - remnant of cellulose-digesting organ, (ii) Coccyx -

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Weismann cut the tails of mice for over twenty generations, yet every time mice were born with normal tails. This showed that acquired characters cannot be inherited, leading him to propose the germpl

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Charles Darwin (1809-1882) was a naturalist who traveled on H.M.S. Beagle at age 22, studying species worldwide. He wrote 'The Origin of Species by Natural Selection' published in 1859 A.D., which exp