Anna Karenina voice sharp criticism of the morality of Darwin's views. 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 (later awarded the title Lord Kelvin), who calculated that it had cooled in less than 100 million years. 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. 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. 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 "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. Impact on economic and political debates While some, like Spencer, used analogy from natural selection as an argument against government intervention in the economy to benefit the poor, others, including Alfred Russel Wallace, argued that action was needed to correct social and economic inequities to level the playing field before natural selection could improve humanity further. Some political commentaries, including Walter Bagehot's Physics and Politics (1872), attempted to extend the idea of natural selection to competition between nations and between human races. Such ideas were incorporated into what was already an ongoing effort by some working in anthropology to provide scientific evidence for the superiority of Caucasians over non-white races and justify European imperialism. Historians write that most such political and economic commentators had only a superficial understanding