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===About Evolution by Natural Selection===
: '''Evolution by natural selection''' is caused by two important factors; [[variation]] and [[heredity]].
: A species will have [[variation]] between [[organism]]s in the [[population]]. This means they will all be slightly different.
: Some [[variation]]s are [[heredity|hereditary]] which means they are passed on from parent to [[offspring]].
| style="height:20px; width:900px; text-align:center;" |This picture shows a series of human skulls starting on the left with a skull from 20 million years ago through to a modern human skull.
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==Key Stage 4==
===Meaning===
'''Evolution by natural selection''' is the process that leads to new [[species]] being formed over thousands of generations.
===About Evolution by Natural Selection===
: '''Evolution by natural selection''' is caused by two important factors; [[variation]] and [[heredity]].
: A [[species]] will have [[variation]] between [[organism]]s in the [[population]]. This means they will all be slightly different.
: Some [[variation]]s are [[heredity|hereditary]] which means they are passed on from parent to [[offspring]].
: If a [[heredity|heritable]] [[variation]] gives a member of the [[species]] an advantage over the others in its environment, then it is more likely to survive and [[Reproduction|reproduce]]. This is [[Natural Selection|natural selection]] where some [[variation]]s cause [[organism]]s to die while other [[variation]]s cause [[organism]]s to have more [[offspring]].
: [[Variation]] can be caused by random [[mutation]]s which occur during [[reproduction]]. If that [[mutation]] provides an advantage to that [[organism]] over others in the [[species]] then it will have more [[offspring]] than others spreading that beneficial [[mutation]]. Over several [[generation]]s that [[mutation]] will be spread throughout the [[species]]. Over time many of these [[mutation]]s occur changing the entire [[population]] until they are no longer the same [[species]] as they were prior to these [[mutation]]s.
===Development of the Theory of Evolution===