Despite the book’s invocation of a Creator, Chambers’s argument was seen as consistent with the supposed materialism, or atheism, of the French Revolution.8 Though most Enlightenment thinkers were Deists, their naturalistic philosophies and anticlericalism had often been read as evidence of atheism. In particular, Baron d’Holbach’s The System of Nature (1770) promised to free men from supernatural beliefs by showing how reason could explain the workings of the universe.9 In d’Holbach’s account, matter was eternal, and all processes related to matter could be attributed to its properties. D’Holbach’s System of Nature represented an extreme view among the philosophes themselves, but the attacks on the clergy and Maximilien Robespierre’s project of secularizing France in the 1790s resulted in the loss of such fine distinctions. The severe reaction against the French Revolution in England meant that science that smacked of atheism not only threatened the Anglican establishment but also had a political dimension that threatened the stability and order of society.
The debate over the 1844 Vestiges, as the historian James Secord has demonstrated, provoked conversations across Britain about a host of issues, including the propriety of women in science, the ability of the masses to grasp science, as well as the role of God in creating life. Darwin studied Vestiges for arguments he needed to address in his own evolutionary treatise, and his observation of the controversy surrounding the 1844 book also made him determined to avoid the charge of having written a popular, rather than scholarly, treatment.10
After Darwin, Western scientists could dismiss neither evolution nor natural selection without serious consideration. Origin’s reach extended well beyond the realm of biology. Contemporary scientific debates about naturalistic processes in geology and physics coalesced around Darwin’s publication. Geologists found the idea of progressive and gradual change problematic, while physicists objected to the time scale implied by natural selection. In these debates, scientists did not always directly invoke either a Christian God or a Creator, but God’s existence formed a powerful subtext.
Charles Lyell’s Principles of Geology, published in three volumes in the early 1830s, had influenced Darwin’s thinking on the age of the Earth, the process of change, and the use of present-day examples in nature to speculate about the past. Lyell’s work established uniformitarianism in geology as opposed to the catastrophism that assumed that disasters punctuated the Earth’s past and were responsible for geological formations like mountains. Catastrophism was consistent with biblical creationism and the Flood myth. For Lyell, unconcerned with the biblical account, slow and steady changes, such as the action of water in forming valleys, marked the Earth’s geological past. But Lyell also rejected the idea of transmutation, or the idea that the simpler forms of life had led to more complex forms, as a violation of the uniformitarian principle that the same forces had always been at work and were directionless.11 On that reading, species were essentially unchanged from their first appearances. By 1859, Lyell had dispelled the sway catastrophism had over geology, but he had also posed powerful arguments against evolution as incompatible with uniformitarianism.12 When he finally accepted evolution in the early 1860s, it was a theistic version that did not apply to humans.13
While Lyell struggled with accepting transmutation, physicists like William Thomson (later Lord Kelvin), who had articulated the principles of thermodynamics in the 1840s and 1850s, rejected natural selection on the grounds that it required the Earth to be far older than it could be. In the 1830s, Lyell did not attempt to date the Earth and cautioned against the tendency to “assign limits” to the amount of time the universe or the Earth had been in existence.14 In the first edition of Origin of Species, Darwin, like Lyell, also avoided naming a specific age but suggested that it had been three hundred million years since the Weald, or a plain, in southern England had lost its trees. Thomson found these apparently limitless dating schemes untenable.
Thomson, along with Rudolf Clausius, had elaborated the second law of thermodynamics, or the idea that heat flows toward cooler objects in an irreversible process, in the early 1850s.15 Clausius named the process “entropy” in an 1865 article that also contained his classic statement of the second law of thermodynamics that “the energy of the universe is constant. The entropy of the universe tends towards a maximum.”16 Scientific detractors to the idea of entropy actually rejected it because it was compatible with a creationist account, arguing instead that the universe was actually infinite.17 Not until the 1880s did a godless “heat death” start to capture the popular imagination in England and the United States. For Thomson, his studies on heat loss meant that the universe must have had a beginning and an end, and he could use his suppositions about the dissipation of energy to date the world in the wake of Darwin’s publication.18
During the 1860s, Thomson published articles that criticized Darwin on the basis that the world could not be as old as Darwin needed it to be for natural selection to have performed its work. In 1862, Thomson estimated that the sun was between one hundred and five hundred million years old and the Earth between twenty million and four hundred million years old, based on the length of time it must have taken for those bodies to cool. By 1868, he had landed on a probable age of the Earth as one hundred million years old, based on what the shape of the Earth suggested about the decline in rotational speed over time. None of these estimates were enough for a slow, evolutionary development of life. Thomson continued refining his arguments and revising the age of the Earth downward for the rest of the century, garnering increased support from geologists and physicists.19
Many of the biologists who disagreed with Darwin’s assertion that natural selection was the driver of evolution also concluded that it defied God’s immanence. The theory of natural selection, insofar as it provided a reasonable explanation as to how life could have evolved without a Creator, was a plausible alternative to the account of creation in the book of Genesis.20 For believers in this alternative “creation story,” the removal of God from the origins of humanity left the future of the human species open to an arbitrary and unplanned series of events, similar to that which had resulted in the evolution of human life.
After Darwin published Origin of Species, evolution largely became the accepted explanation in the scientific community for how life had developed, but the social and theological implications of evolutionary theory troubled many scientists in the nineteenth century. The notion that humans had evolved from apes prompted questions about human nature. Such questions could undermine the rule of elites by challenging their birthright or could deny an innate moral sense to humans.21 In the first edition of Origin, Darwin wrote, “I must premise, that I have nothing to do with the origin of the primary mental powers, any more than I have with that of life itself.”22 But the intensity of that statement paled before others, such as his closing remark: “Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”23
Though Darwin did not directly discuss human evolution until 1871 in The Descent of Man, it did not take much creativity to conclude that natural selection had worked upon humans just as it had on animals. Doubts about natural selection persisted until the 1930s and 1940s. One of the main obstacles to the acceptance of natural selection among scientists was a continued view of evolution as progressive.24 In the decades after Darwin first proposed natural selection, non-Darwinian theories of evolution had upheld progress as inherent within the process and did not require as long of a time scale for their operation flourished.25
By the end of the 1800s, “neo-Darwinian” became the label for scientists who explained evolution through the transmission of characteristics produced by natural selection.26 Darwin himself did not attribute evolutionary change to natural selection alone, and at times he leaned toward aspects of Lamarckism, or the idea that