Evolution

• Evolutionary Biology


  The study of history of life forms on earth
• Evolution


  Changes in flora and fauna that have occurred over millions of years on earth
• The origin of life is considered a unique event in the history of the universe
• The universe is vast, and the earth is almost only a speck in comparison
• The Big Bang theory attempts to explain the origin of the universe
• Earth was formed about 4.5 billion years back
• Life appeared 500 million years after the formation of earth, i.e., almost four billion years back
• Panspermia


  The idea that life came from outside the earth
• Spontaneous generation


  The theory that life came out of decaying and rotting matter
• Louis Pasteur demonstrated that life comes only from pre-existing life
• Chemical evolution


  The formation of diverse organic molecules from inorganic constituents
• In 1953, S.L. Miller created similar conditions in a laboratory scale and observed the formation of amino acids
• The first non-cellular forms of life could have originated 3 billion years back
• The first cellular form of life did not possibly originate till about 2000 million years ago
• Special creation


  The theory that all living organisms were created as such
• Natural selection


  The mechanism of evolution proposed by Charles Darwin
• Earth is very old, not thousands of years as was thought earlier but billions of years old
• Fossils


  Remains of hard parts of life-forms found in rocks
• Paleontological evidence


  The study of fossils in different sedimentary layers indicating the geological period in which they existed
• Embryological support for evolution


  The observation of certain features during embryonic stage common to all vertebrates that are absent in adult
• Homology


  Similarities in the anatomical structure of organisms indicating common ancestry
• Analogy


  Similarities in the function of structures in organisms, but not in their anatomical structure
• Similarities in proteins and genes performing a given function among diverse organisms give clues to common ancestry
• Homology


  Based on divergent evolution
• Analogy


  Refers to a situation exactly opposite of homology
• Analogous structures


  • Wings of butterfly and of birds
  • Eye of the octopus and of mammals
  • Flippers of Penguins and Dolphins
  • Sweet potato (root modification) and potato (stem modification)
• Analogous structures are a result of convergent evolution - different structures evolving for the same function and hence having similarity
• Man has bred selected plants and animals for agriculture, horticulture, sport or security
• Man has domesticated many wild animals and crops
• Intensive breeding programme has created breeds that differ from other breeds (e.g., dogs) but still are of the same group
• If within hundreds of years, man could create new breeds, could not nature have done the same over millions of years?
• In a collection of moths made in 1850s, i.e., before industrialisation set in, there were more white-winged moths on trees than dark-winged or melanised moths
• In the collection carried out from the same area, but after industrialisation, i.e., in 1920, there were more dark-winged moths in the same area, i.e., the proportion was reversed
• Predators will spot a moth against a contrasting background
• During post-industrialisation period, the tree trunks became dark due to industrial smoke and soots. Under this condition the white-winged moth did not survive due to predators, dark-winged or melanised moth survived
• Before industrialisation set in, thick growth of almost white-coloured lichen covered the trees - in that background the white winged moth survived but the dark-coloured moth were picked out by predators
• Lichens can be used as industrial pollution indicators. They will not grow in areas that are polluted
• Moths that were able to camouflage themselves, i.e., hide in the background, survived
• In areas where industrialisation did not occur e.g., in rural areas, the count of melanic moths was low
• In a mixed population, those that can better-adapt, survive and increase in population size