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Charles Darwin in 1868. Darwinism is a term used to describe a theory of biological evolution developed by the English naturalist Charles Darwin (1809–1882) and others. The theory states that all species of organisms arise and develop through the natural selection of small, inherited variations that increase the individual's ability to compete, survive, and reproduce.
Professor of biology Jerry Coyne sums up biological evolution succinctly: [3]. Life on Earth evolved gradually beginning with one primitive species – perhaps a self-replicating molecule – that lived more than 3.5 billion years ago; it then branched out over time, throwing off many new and diverse species; and the mechanism for most (but not all) of evolutionary change is natural selection.
In 1858 Charles Darwin and Alfred Russel Wallace published a new evolutionary theory, explained in detail in Darwin's On the Origin of Species (1859). Darwin's theory, originally called descent with modification is known contemporarily as Darwinism or Darwinian theory.
Evolution is the change in the heritable characteristics of biological populations over successive generations. [1] [2] It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certain characteristics becoming more or less common within a population over successive generations. [3]
Darwin's theory of natural selection laid the groundwork for modern evolutionary theory, and his experiments and observations showed that the organisms in populations varied from each other, that some of these variations were inherited, and that these differences could be acted on by natural selection.
The mediaeval great chain of being as a staircase, implying the possibility of progress: [1] Ramon Lull's Ladder of Ascent and Descent of the Mind, 1305. Alternatives to Darwinian evolution have been proposed by scholars investigating biology to explain signs of evolution and the relatedness of different groups of living things.
In eight years of work on barnacles, Darwin's theory helped him to find "homologies" showing that slightly changed body parts served different functions to meet new conditions, and in some genera he found minute males parasitic on hermaphrodites, showing an intermediate stage in evolution of distinct sexes. [127]
Barnacles from Darwin's collection, sent as a gift to Japetus Steenstrup and Johan Georg Forchhammer in 1854, Zoological Museum of Copenhagen. A single barnacle species was left to describe, and on 1 October 1846 Darwin began a paper on it, [27] working on dissecting with the assistance of Hooker who was now at Kew.