Charles Darwin was aware of the severe reaction in some parts of the scientific community against the suggestion made in “Vestiges of the Natural History of Creation” that humans had arisen from animals by a process of transmutation. Therefore he almost completely ignored the topic of human evolution in “The Origin of Species”. Despite this precaution, the issue featured prominently in the debate that followed the book’s publication. For most of the first half of the 19th century, the scientific community believed that, although geology had shown that the Earth and life were very old, human beings had appeared suddenly just a few thousand years before the present. However, a series of archaeological discoveries in the 1840s and 1850s showed stone tools associated with the remains of extinct animals. By the early 1860s, as summarized in Charles Lyell‘s 1863 book “Geological Evidences of the Antiquity of Man”, it had become widely accepted that humans had existed during a prehistoric. This view of human history was more compatible with an evolutionary origin for humanity than was the older view.
Therefore the debate that immediately followed the publication of “The Origin of Species” centred on the similarities and differences between humans and modern apes. Carolus Linnaeus had been criticised in the 18th century for grouping humans and apes together as primates in his ground breaking classification system. Richard Owen vigorously defended the classification suggested by Cuvier and Johann Friedrich Blumenbach that placed humans in a separate order from any of the other mammals, which by the early 19th century had become the orthodox view. On the other hand, Thomas Henry Huxley sought to demonstrate a close anatomical relationship between humans and apes. Charles Lyell and Alfred Russel Wallace agreed that humans shared a common ancestor with apes, but questioned whether any purely materialistic mechanism could account for all the differences between humans and apes, especially some aspects of the human mind.
In 1871, Darwin published “The Descent of Man, and Selection in Relation to Sex”, which contained his views on human evolution. Darwin argued that the differences between the human mind and the minds of the higher animals were a matter of degree rather than of kind. He argued that all the differences between humans and apes were explained by a combination of the selective pressures that came from our ancestors moving from the trees to the plains, and sexual selection.