Editing On the Origin of Species (section)

====Challenges to natural selection====
There were serious scientific objections to the process of [[natural selection]] as the key mechanism of evolution, including [[Carl Nägeli]]'s insistence that a trivial characteristic with no adaptive advantage could not be developed by selection. Darwin conceded that these could be linked to adaptive characteristics. His estimate that the [[age of the Earth]] allowed gradual evolution was disputed by [[William Thomson, 1st Baron Kelvin|William Thomson]] (later awarded the title Lord Kelvin), who calculated that the [[Sun]], and therefore life on Earth, was only about 100 million years old.<ref>{{harvnb|Kragh|2016|pp=11–12}}</ref> Darwin accepted [[blending inheritance]], but [[Fleeming Jenkin]] calculated that as it mixed traits, natural selection could not accumulate useful traits. Darwin tried to meet these objections in the fifth edition. [[St. George Jackson Mivart|Mivart]] supported directed evolution, and compiled scientific and religious objections to natural selection. In response, Darwin made considerable changes to the sixth edition. The problems of the age of the Earth and heredity were only resolved in the 20th century.<ref name=miv/><ref>{{harvnb|Bowler|2003|pp=198–200, 234–236}}</ref>

By the mid-1870s, most scientists accepted evolution, but relegated natural selection to a minor role as they believed evolution was purposeful and progressive. The range of evolutionary theories during "[[the eclipse of Darwinism]]" included forms of "[[Saltation (biology)|saltationism]]" in which new species were thought to arise through "jumps" rather than gradual adaptation, forms of [[orthogenesis]] claiming that species had an inherent tendency to change in a particular direction, and forms of neo-Lamarckism in which inheritance of acquired characteristics led to progress. The minority view of [[August Weismann]], that natural selection was the only mechanism, was called [[neo-Darwinism]]. It was thought that the rediscovery of [[Mendelian inheritance]] invalidated Darwin's views.<ref>{{harvnb|Bowler|2003|p=225}}</ref><ref name=Quammen205-234>{{Harvnb|Quammen|2006|pp=205–234}}</ref>