Evolution

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Theories of Evolution

Darwins theory of evolution explains how life on earth has changed over geological time. The theory is supported by evidence from fossils and by the rapipd changes that can be seen to occur in microorganisms such as antibiotic-resistant bacteria. 

Different species have developed over time from simple life forms. 

Darwin's Theory

Caused a lot of controversy. Conflicted with religious veiws, Not enough scientific evidence, Took 50 years after Darwins theory to discover how inheritence and variation worked.

Lamaracks theory 

  • A characteristic which is used more and more by an organism becomes bigger and stronger, and one that not used eventually disappears 
  • Any feature of an organism that is improved through use is passed to its offspring.

We now know that in most cases this type of inheritence cannot happen.

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Similarities and Differences

Different organisms can be classified by studying their similarities and differences. These studies also help us understand the evolutionary relationships between organisms

Evolutionary Trees

Represent the relationships between organisms. (http://www.bbc.co.uk/schools/gcsebitesize/science/images/aqa_bio_cladograph.jpg)

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Natural Selection

  • Individuals in a species show a wide range of variation
  • This variation is because of differences in their genes
  • Individuals with characteristics most suited to the enviroment are more likely to survive and reproduce
  • The genes that allow these individuals to be successful are passed to their offspring

Variation can be caused by both genes and the enviroment. But it is only variation caused by genes that can be passed onto the next generation

Conditions on Earth 

Life on earth today exsits because of the conditions that were present when life was evolving. Natural selection could have had very different results a long time ago. e.g. If the earth had been hotter, colder, bigger, smaller, our bodies would have changed to suit this condition 

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Evidence for Evolution: Rapid Changes

Mutations cause changes in genes. When new forms of a gene appear because of mutation, a rapid changes in species may happen if the enviroment changes.

Peppered Moths

Before the industrial revolution in Britian, most peppeed moth's were of the pale variety. They were camouflaged against the pale birch trees that they rest on. Moths with mutant black colouring were easily spotted and eaten by birds. 

Airborne pollution in industrial areas blackened the birch tree with sook. This meant that the mutant black moths were now camouflaged, while the white variety became more vunerable to predators. Overtime the black peppered moths have become far more numerous in urban areas.

Antibiotic-resistant bacteria

Microorganisms such as bacteria and viruses reproduce very quickly and can evolve very fast e.g. Bacterium 'E . coli'. Its DNA can be damaged or changed when it reproduces. Most of the time this causes the death of the bacterial cell. Occasionally the mutation is beneficial for the bacterial cell. e.g. It may allow resisitance to an antibiotic  

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