Evolution

Evolution

1. Darwin

   • • Darwin’s theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago.
   • • These first organisms were very simple single-celled organisms, similar to bacteria.
   • • The theory of evolution by natural selection was only gradually accepted because:
     • the theory challenged the idea that God made all the animals and plants that live on Earth
       • there was insufficient evidence at the time the theory was published to convince many scientists
         • the mechanism of inheritance and variation was not known until 50 years after the theory was published.
   • Natural Selection
     • • Organisms produce large numbers of offspring
       • • Individual organisms within a particular species may show a wide range of variation because of differences in their genes
         • • There is a struggle for all organisms to exist (eg. Predation)
           • • Individuals with characteristics most suited to the environment are more likely to survive to breed successfully
             • The genes which have enabled these individuals to survive are then passed on to the next generation
               • • Gradually, this can result in changes in the characteristics of a species.

2. Lamarck

   • • He proposed a theory of acquired characteristics.
   • • He argued that an individual’s characteristics will change over its lifetime due to amount of use.
     • • Eg. Giraffes necks get longer due to stretching for leaves.
   • • Then he suggested that these characteristics could be inherited.
   • We now know that in the vast majority of cases this type of reproduction cannot occur. • Changes in the body do not change the genes.

3. Classification

   • • Studying the similarities and differences between organisms allows us to classify living organisms into animals, plants and microorganisms.
   • • This helps us to understand evolutionary and ecological relationships
   • • Evolutionary trees (models) are used to represent the relationships between organisms.
   • This tree indicates how long ago the ancestors of ape species diverged from each other. It indicates that humans share a common ancestor with chimpanzees more recently than with any other ape species.

4. Mutations

   • • How do mutations occur?
     • • Errors occur when the DNA is replicated prior to cell division.
       • • Errors may occur when chromosomes are separated during cell division.
   • • What do mutations do?
     • • Genes control the synthesis of proteins.
       • • Therefore a change in a gene or a new sequence of genes can result in different proteins being synthesised.
         • • This can change a characteristic.
   • • Most mutations are harmful or fatal.

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