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Theories of evolution

  • All species of living things have evolved from simple life forms. These simple forms developed more than 3 billion years ago
  • Darwin's theory states that evolution takes place by a process of natural selection
  • Jean-Baptiste Lamarck suggested a theory called "the inheritance of acquired characteristics". Lamarck's theory stated that characteristics which developed during an organisms's lifetime can be passed on to the next generation. People found this difficult to believe. For example, if two parent were to build up their muslces in the gym, Lamarck's theory would predict that this characteristic would be passed on to their offspring
  • Charles Darwin suggested the theory of "natural selection" after he had made a journey to the Galapagos Islands. He recorded many observations about life on the islands.
  • Darwin's theory stated that small change in organisms took place over a very long time. All organisms in a species vary and therefore some are more likely to survive (natural selection). Those that are best adapted breed and pass on their characteristics
  • Darwin did not know about genes. We can now say that the best adapted organisms survive to breed. They are the ones that pass on their genes to the next generation
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Accepting Darwin's ideas

  • Darwin's theory of evolution was only gradually accepted for serveral reasons:
  • The theory of natural selection challeneged the idea that God made all the animals and plants that live on Earth
  • Many scientists were not convinced because they still did not think there was sufficient evidence for the theory
  • Darwin could not explain why there was variety in organisms, or how inheritance worked. Scientists did not know about genes and genetics until about 50 years later
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Natural selection

  • Natural selection works because the fittest organisms surive to breed
  • If a gene changes, the new characteristic may enable the organism to survive better
  • Sometimes a gene accidentally changes and becomes a new form of the gene. These changes are called mutations. If the mutated gene controls a characterisitic which makes the organism better adapted to the environment then it will be passed on to the offspring
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Classification and evolution

  • We can classify organisms into groups by comparing their similarities and differences
  • Classification helps us to understand evolutionary and ecological relationships
  • Biologists study the similarities and differences between organisms in order to classify them. The system used is called the natural classification system
  • The easiest system to understand is one which starts with large groups and splits these up gradually into smaller ones. The largest groups are called kingdoms
  • The main kingdoms are:
  • The plant kingdom
  • The animal kingdom
  • The kingdoms which contain the microorganisms
  • The smallest group in the classification system is the species
  • Members of a species are very similar and can breed together to produce fertile offspring
  • Evolutionary trees are models that can be drawn to show the relationships between different groups of organisms
  • When new evidence is found, biologist may modify these evolutionary reationships
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