Theory Of Evolution

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Theory Of Evolution

• What is evolution?

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The Origin Of Species

• The tumult in the middle of the 19 century was
  accompanied by the publication of Darwins Origin
  of species. The principal topic of this work was
  that the life forms we see today are the result
  of millions of years of evolution by a process
  Darwin called natural selection. The work had a
  revolutionary impact on Western thought which has
  still not been fully assimilated.

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A Process Of Continuous Change

• Biological evolution is a genetic change in a
  population from one generation to another. The
  speed and direction of change is variable with
  different species lines and at different times.
  Continuous evolution over many generations can
  result in the development of new varieties and
  species. Likewise, failure to evolve in response
  to environmental changes can, and often does,
  lead to extinction. All life forms, including
  people, evolved from earlier species.
  Furthermore, all still living species of
  organisms continue to evolve today.

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The Fossil Record

• The remains of animals and plants found in
  sedimentary deposits provide a record of past
  changes through time. The existence of fossils
  confirms that species are not fixed but can
  evolve into other species over time. The evidence
  also shows that what has appeared to be gaps in
  the fossil record is due to incomplete specific
  species lines. The most of these so-called
  missing links in the chain of evolution are
  filled with transitional fossil specimens.

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Geographic Distribution Of Related Species

• Another clue of evolution is found in the
  natural geographic distribution of related
  species. It is clear that major isolated land
  areas and island groups often evolved their own
  distinct plant and animal communities. For
  instance, before humans arrived 60-40000 years
  ago, Australia had more than 100 species of
  kangaroos, koalas and other marsupials but didnt
  have none of the most advanced terrestrial
  placental mammals such as dogs, cats, bears,
  horses. Land mammals were entirely absent from
  the isolated island that make up Hawaii and New
  Zealand. Each of these places had a great number
  of plant, insect and bird species that were found
  nowhere else in the world. The most likely
  explanation for the existence of Australias, New
  Zealands, and Hawaiis biotic environments is
  that the life forms in these areas have been
  evolving in isolation from the rest of the world
  for millions of years.

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Pre-Darwinian Theories
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Carolus Linneous

• The Swedish botanist Karl von Linné(1707-1778)
  was the first class scientist. His most important
  contribution to science was is logical
  classification system for all living beings he
  proposed in is book Systema Naturae(1735). He
  described plants and animals on the basis of
  physical appearance and classified them
  relatively to each other according to the degree
  of their similarities. He used a binomial
  nomenclature in naming them. Organisms were given
  two Latin names genus (usually written with a
  capital letter) and species. Each genus could
  have many related species and it was also part of
  larger categories of living beings.

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Jean Baptiste De Monet , Chevalier De Lamarck

• The first evolutionist who started his ideas
  about the processes leading by the logical change
  was a French aristocrat, J. B. Lamarck(
  1744-1829). Unfortunately, his theory about these
  processes was incorrect. Lamarck believed that
  microscopic organisms appeared spontaneously from
  inanimate materials and than evolved gradually
  and progressively into more complex forms through
  a constant tension to the perfection. Lamarck
  thought that humans were the ultimate product of
  this evolution. He believed that evolution was
  mostly due to the inheritance of acquired
  characteristics as creatures adapted to their
  environments. He thought that giraffes evolved
  their long necks by each generation stretching
  further to get leaves in trees and that this
  change in body shape was then inherited. Lamarck
  also believed that creatures could develop new
  organs or change the structure and function of
  old ones as a result of their use or disuse.

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George Cuvier

• A French scientist, George Cuvier(1769-1832),
  discredited Lamarcks theory. Cuvier did not
  reject the idea that there had been earlier life
  forms. He was the first scientist to describe
  extinctions of ancient animals. However, he
  rejected the idea that their existence implied
  that evolution had occurred he maintained the
  fixity of species. Cuvier advocated the theory
  of catastrophism. This held that there have been
  violent and sudden natural catastrophes such as
  great floods and the rapid formation of major
  mountain chains. Plants and animals living in
  those parts of the world where such events
  occurred, were often killed off according to
  Cuvier. Then new life forms moved in from other
  areas. As a result, the fossil record for a
  region show, abrupt changes in species.

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Charles

• Darwin

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• Darwin had observed the wide variety of
  finches and the unusual types of tortoises and
  iguanas, found on the Galapagos islands. He also
  had a knowledge of comparative anatomy and an
  understanding of previously circulating theories
  of evolution, which were suggestive but flawed.
  It was from these elements that Darwin created
  his powerful new synthesis.

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• According to Darwins theory, initially slight
  variations in populations of organisms may give
  certain individuals an advantage in adapting to
  their environment. Any such advantage may be
  passed on from parents to offsprings, causing the
  advantageous traits to proliferate in subsequent
  generations. Meanwhile, the subsequent
  generations of organisms may eventually come from
  their own species. Species are caused by the
  struggle for existence in specific environmental
  conditions. For example, its clear that Bengal
  tigers, Siberian tigers and African lions are
  probably descended from the same predecessor, but
  they now belong to different species of the genus
  felis.

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• This work has been produced by
• Rosa Scanniffio
• Flavia Ndriollari
• Orsolinda Perrucci
• Rosanna Lopedota