After Darwin graduated with a bachelor of arts degree in 1831, botany professor John Stevens Henslow recommended him for a naturalist’s position aboard the HMS Beagle. The ship was to take a five-year survey trip around the world. Over the course of the trip, Darwin collected a variety of natural specimens, including birds, plants and fossils. Through hands-on research and experimentation, he had the unique opportunity to closely observe principles of botany, geology and zoology. The Pacific Islands and Galapagos Archipelago were of particular interest to Darwin, as was South America.
Upon his return to England in 1836, Darwin began to write up his findings in the Journal of Researches. He began to develop a revolutionary theory about the origin of living beings that was contrary to the popular view of other naturalists at the time. Other naturalists believed that all species either came into being at the start of the world, or were created over the course of natural history. In either case, the species were believed to remain much the same throughout time. Darwin, however, noticed similarities among species all over the globe, along with variations based on specific locations, leading him to believe that they had gradually evolved from common ancestors. Combining a series of basic facts (food is limited and animals compete for it) and inferences (species have to fight to continue on), Darwin reasoned that animals would continue to exist on based on their ability to survive and reproduce. This process was called as “natural selection,” where species that successfully adapted to meet the changing requirements of their natural habitat thrived, while those that failed to evolve and reproduce died off.
On November 24, 1859, Darwin published a detailed explanation of his theory in his best-known work, “On the Origin of Species by Means of Natural Selection”.During the next century, DNA studies revealed evidence of his theory of evolution, although controversy surrounding its conflict with Creationism—the religious view that all of nature was born of God—still abounds today.
Reference:
http://www.biography.com/people/charles-darwin-9266433#voyage-on-the-hms-beagle
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