Theory:

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Charles Darwin
  
Charles Darwin (\(1809-1882\)) was a renowned naturalist and philosopher of the \(18th\) century. In \(1809\), he was born in England. He was captivated by nature while in college because of his connection with Professor J.S.Henslow. The British Admiralty planned a 5-year exploratory expedition around South America on the H.M.S. Beagle (a ship that sailed around the world) at the time.
 
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H.M.S Beagle
 
As Dr Henslow was asked to nominate a young naturalist for the voyage, he nominated Darwin. In the five years (1831-1835) voyage period, Darwin explored flora and fauna of many continents and islands.
 
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Map showing the voyage of HMS beagle

He also visited the Galapagos Islands and Pacific islands of volcanic origin and are called "a living laboratory of evolution."
 
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Galapagos islands
  
Darwin thoroughly recorded the natural history of the land, plants, and animals in the locations he visited. He spent 20 years and developed the theory of natural selection.
 
In \(1859\), Darwin published his observations and results under the title "Origin of Species." Darwin's book proves the existence of evolution. It elaborates on the hypothesis of Natural Selection as a mechanism for evolutionary change.
Reference:
https://commons.wikimedia.org/wiki/File:Charles_Darwin,_English_naturlist,_colored.jpg
https://commons.wikimedia.org/wiki/File:Voyage_of_the_Beagle.jpg
https://www.flickr.com/photos/nunataak/3348740075