Introduction to evolution: Difference between revisions

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Darwin gained extensive experience as he collected and studied the natural history of life forms from distant places. Through his studies, he formulated the idea that each species had developed from ancestors with similar features. In 1838, he described how a process he called natural selection would make this happen.<ref name="Confessions">{{cite journal |last=Eldredge |first=Niles |author-link=Niles Eldredge |date=Spring 2006 |title=Confessions of a Darwinist |url=http://www.vqronline.org/vqr-portfolio/confessions-darwinist |journal=[[Virginia Quarterly Review]] |___location=Charlottesville, VA |publisher=[[University of Virginia]] |volume=82 |issue=2 |pages=32–53 |access-date=2015-01-07}}</ref>

The size of a population depends on how much and how many resources are able to support it. For the population to remain the same size year after year, there must be an equilibrium, or balance between the population size and available resources. Since organisms produce more offspring than their environment can support, not all individuals can survive out of each generation. There must be a competitive struggle for resources that aid in survival. As a result, Darwin realised that it was not chance alone that determined survival. Instead, survival of an organism depends on the differences of each individual organism, or "traits," that aid or hinder survival and reproduction. Well-adapted individuals are likely to leave more offspring than their less well-adapted competitors. Traits that hinder survival and reproduction would ''disappear'' over generations. Traits that help an organism survive and reproduce would ''accumulate'' over generations. Darwin realised that the unequal ability of individuals to survive and reproduce could cause gradual changes in the population and used the term ''natural selection'' to describe this process.<ref name="Geographic" /><ref name="wyhe" />

Observations of variations in [[animal]]s and [[plant]]s formed the basis of the theory of natural selection. For example, Darwin observed that [[Orchidaceae|orchids]] and [[insect]]s have a close relationship that allows the [[pollination]] of the plants. He noted that orchids have a variety of structures that attract insects, so that [[pollen]] from the [[flower]]s gets stuck to the insects' bodies. In this way, insects transport the pollen from a male to a female orchid. In spite of the elaborate appearance of orchids, these specialised parts are made from the same basic structures that make up other flowers. In his book, ''[[Fertilisation of Orchids]]'' (1862), Darwin proposed that the orchid flowers were adapted from pre-existing parts, through natural selection.<ref>{{cite web |url=http://darwin-online.org.uk/EditorialIntroductions/Freeman_FertilisationofOrchids.html |title=Fertilisation of Orchids |last=van Wyhe |first=John |year=2002 |work=The Complete Work of Charles Darwin Online |oclc=74272908 |access-date=2008-01-07}}</ref>