Editing On the Origin of Species (section)

===Further development===
{{See also|Development of Darwin's theory}}
[[File:Charles Darwin - Pigeon skulls.png|thumb|Darwin researched how the skulls of different pigeon breeds varied, as shown in his ''Variation of Plants and Animals Under Domestication'' of 1868.]]

Darwin continued to research and extensively revise his theory while focusing on his main work of publishing the scientific results of the ''Beagle'' voyage.<ref name=vw186/> He tentatively wrote of his ideas to Lyell in January 1842;<ref>{{Harvnb|Desmond|Moore|1991|p=292}}</ref> then in June he roughed out a 35-page "Pencil Sketch" of his theory.<ref>{{harvnb|Browne|1995|pp=436–437}}</ref> Darwin began correspondence about his theorising with the botanist [[Joseph Dalton Hooker]] in January 1844, and by July had rounded out his "sketch" into a 230-page "Essay", to be expanded with his research results and published if he died prematurely.<ref>{{Harvnb|van Wyhe|2007|p=188}}</ref>

In November 1844, the anonymously published [[popular science]] book ''[[Vestiges of the Natural History of Creation]]'', written by Scottish journalist [[Robert Chambers (journalist)|Robert Chambers]], widened public interest in the concept of transmutation of species. ''Vestiges'' used evidence from the fossil record and embryology to support the claim that living things had progressed from the simple to the more complex over time. But it proposed a linear progression rather than the branching common descent theory behind Darwin's work in progress, and it ignored [[adaptation]]. Darwin read it soon after publication, and scorned its amateurish geology and zoology,<ref>{{Citation|url=http://www.darwinproject.ac.uk/darwinletters/calendar/entry-814.html#back-mark-814.f5|title=Darwin Correspondence Project – Letter 814—Darwin, C. R. to Hooker, J. D., (7 January 1845)|access-date=24 November 2008}}</ref> but he carefully reviewed his own arguments after leading scientists, including Adam Sedgwick, attacked its morality and scientific errors.<ref>{{harvnb|Browne|1995|pp=461–465}}</ref> ''Vestiges'' had significant influence on public opinion, and the intense debate helped to pave the way for the acceptance of the more scientifically sophisticated ''Origin'' by moving evolutionary speculation into the mainstream. While few naturalists were willing to consider transmutation, [[Herbert Spencer]] became an active proponent of Lamarckism and progressive development in the 1850s.<ref>{{Harvnb|Bowler|2003|pp=135–140}}</ref>

Hooker was persuaded to take away a copy of the "Essay" in January 1847, and eventually sent a page of notes giving Darwin much-needed feedback. Reminded of his lack of expertise in [[Taxonomy (biology)|taxonomy]], Darwin began an eight-year study of [[barnacle]]s, becoming the leading expert on their classification. Using his theory, he discovered [[homology (biology)|homologies]] showing that slightly changed body parts served different functions to meet new conditions, and he found an [[Androdioecy|intermediate stage]] in the evolution of [[Gonochorism|distinct sexes]].<ref name=bowl169>{{Harvnb|Bowler|2003|pp=169–173}}</ref><ref>{{Harvnb|Darwin|1958|pp=[http://darwin-online.org.uk/content/frameset?viewtype=text&itemID=F1497&pageseq=121 117–121]}}</ref>

Darwin's barnacle studies convinced him that variation arose constantly and not just in response to changed circumstances. In 1854, he completed the last part of his ''Beagle''-related writing and began working full-time on evolution. He now realised that the branching pattern of [[Genetic divergence|evolutionary divergence]] was explained by natural selection working constantly to improve adaptation. His thinking changed from the view that [[Allopatric speciation|species formed in isolated populations only]], as on islands, to an emphasis on [[Sympatric speciation|speciation without isolation]]; that is, he saw increasing specialisation within large stable populations as continuously exploiting new [[ecological niche]]s. He conducted empirical research focusing on difficulties with his theory. He studied the developmental and anatomical differences between different breeds of many domestic animals, became actively involved in [[fancy pigeon]] breeding, and experimented (with the help of his young son [[Francis Darwin|Francis]]) on ways that plant seeds and animals might disperse across oceans to colonise distant islands. By 1856, his theory was much more sophisticated, with a mass of supporting evidence.<ref name=bowl169/><ref>{{harvnb|Quammen|2006|pp=138–142}}</ref>