Evolution

    Cards (36)

    • Evolutionary Biology is the study of history of life forms on earth
    • Evolution
      Changes in flora and fauna that have occurred over millions of years on earth
    • To understand the changes in flora and fauna, we must have an understanding of the context of origin of life, i.e., evolution of earth, of stars and indeed of the universe itself
    • The universe is almost 20 billion years old
    • Huge clusters of galaxies comprise the universe
    • Galaxies contain stars and clouds of gas and dust
    • Considering the size of universe, earth is just a speck
    • Big Bang theory
      Attempts to explain the origin of the universe, it talks of a similar huge explosion in physical terms
    • There was an atmosphere on early earth
    • Water, methane, carbon dioxide and ammonia released from molten covered the surface of early earth
    • The UV rays from the sun broke up water into Hydrogen and Oxygen, and the lighter H escaped
    • Oxygen combined with ammonia and methane to form water, CO2, and others
    • The ozone layer was formed as the earth cooled, and the water vapor fell as rain to fill all the depressions and form oceans
    • Life appeared 500 million years after the formation of earth, i.e., almost 4 billion years have passed since the formation of earth
    • Theories about the origin of life
      • Life came from outer space (Panspermia)
      • Life came out of decaying and rotting matter (Spontaneous generation)
      • Life formed from pre-existing non-living organic molecules (Chemical evolution)
    • Louis Pasteur demonstrated that life comes only from pre-existing life, and dismissed the theory of spontaneous generation
    • Oparin and Haldane proposed that the first form of life could have come from pre-existing non-living organic molecules and that formation of life was preceded by chemical evolution
    • In 1953, S.L. Miller created similar conditions in a laboratory scale and observed the formation of amino acids
    • Analysis of meteorite content also revealed similar organic compounds, indicating that similar processes are occurring elsewhere in space
    • The first non-cellular forms of life could have originated 3 billion years back, and would have been giant molecules (RNA, Protein, etc.)
    • Fossils are formed when an organism dies and becomes buried under sediment or rock.
    • The first cellular form of life did not possibly originate till about 2000 million years ago
    • All life forms were in water environment only
    • The version of a biogenesis, i.e., the first form of life arose slowly through evolutionary forces from non-living molecules is accepted by majority
    • Special creation theory
      • All living organisms (species or types) that we see today were created as such
      • The diversity was always the same since creation and will be the same in future also
      • Earth is about 4000 years old
    • The special creation theory was strongly challenged during the nineteenth century
    • Based on observations made during a sea voyage in a sail ship called H.M.S. Beagle round the world, Charles Darwin concluded that existing living forms share similarities to varying degrees not only among themselves but also with life forms that existed millions of years ago
    • There had been extinctions of different life forms in the years gone by just as new forms of life arose at different periods of history of earth
    • There has been gradual evolution of life forms
    • Any population present a variety of traits (some to survive, some to reproduce, etc.) would allow natural selection to operate, with those traits that allow better survival and reproduction being selected for, and hence are seen in greater numbers in the next generation
    • This is the mechanism of evolution by natural selection as proposed by the naturalist Charles Darwin
    • The conclusion that life forms have evolved from simpler to more complex types of creatures over long periods of time is based on the similarities observed among living organisms and between them and fossils of extinct life forms
    • Evidence for evolution of life forms on earth has come from the study of fossils preserved in the earth's crust, which provide a glimpse into the diversity of life forms that existed during different geological periods
    • A study of fossils shows that life forms have undergone changes in their morphology (body structure) over time, with more complex life forms appearing in the later geological periods
    • The evolutionary history of life on earth spans billions of years, with the earliest cellular life forms appearing about 3.5 billion years ago
    • The study of fossils and the geological record provides insights into how life forms have evolved through the process of natural selection, with the emergence of new species and the gradual disappearance of others over time