In the United States wealthy tycoons funded fossil-hunting expeditions and new natural history museums to display their discoveries. Dinosaurs from the Western states dramatically transformed the way the ascent of life could be represented because they were quite unlike any living reptiles and confirmed that the ‘tree of life’ had many more branches, some of which had disappeared completely. There was increasing evidence of relatively abrupt transitions in the earth’s history, forcing geologists and evolutionists to reconsider their impression that change had been more or less continuous. As the tree of life became more complex, the assumption that the human species was the inevitable outcome of progressive evolution became less plausible. Although non-Darwinian theories were retained by some authorities, the new vision of evolution came to seem more compatible with Darwin’s vision of an open-ended and less predictable process.

Newspapers expanded around 1900 to reach a wider readership, often reporting sensationalized stories about science. Attacks on the Darwinian theory of natural selection intensified, leading to claims that the theory was on its deathbed. Lamarckism remained active along with the theory of directed variation (orthogenesis), both presented as less materialistic than Darwinism. New alternatives appeared, including the ‘mutation theory’ (evolution by jumps) and genetics, which was at first presented as a threat to Darwinism rather than a supporting factor. In the 1920s a new surge of creationism in the United States intensified the attack on Darwinian materialism, culminating in the widely reported trial of J. T. Scopes. The same critiques appeared in a less muted form in Britain. The Darwinian ‘struggle for existence’ remained a source of anxiety for those who feared a potential threat to moral values and social stability.

In this chapter I take a close look at the early lineage thinking of paleontologists and their attempts to infer evolution from stratigraphic sequences of fossils. Linear thinking with fossils emerged as a core component of the traditional paleontological method in the second half of the nineteenth century. It was taken to extremes by orthogeneticists, and I use the late-nineteenth-century debate between Franz Hilgendorf and Alpheus Hyatt about the famous freshwater Miocene Steinheim snails as a case study for looking at competing forms of lineage thinking. But it was in fact the straight-thinking orthogeneticist Othenio Abel who helped resolve the conundrum of how branching evidence can shed light on the evolution of linear lineages.