The last step in the ascent of the chain of being was from the apes (considered as the highest animals) to humans. In the eighteenth century the linear model of the chain was applied to this transition by depicting the non-European races as intermediate stages between the apes and the highest human type. Nineteenth-century anthropologists used various characters, especially skull size and shape, to give an appearance of scientific credibility to the supposed racial hierarchy. Early theories of evolution often treated the 'lower' races as relics of earlier stages in the origin of humanity. When evolution was represented as a branching tree, the concept of parallelism was invoked to imply that some branches of humanity had not advanced as rapidly up the scale as others. Europeans' sense of their own racial superiority was thus preserved in the post-Darwinian era by converting the chain of being into an abstract scale of mental development ascended by several forms but at different rates.

The chain of being depicted creation as a linear hierachy of living forms from the simplest up to the human. In the eighteenth century it was 'temporalized' to give a model for the history of life on earth implying that humanity was the last and highest product of the creative process. This image of development was boosted by a comparison with the growth of the embryo to maturity. Early theories of evolution continued to present the process as an ascent towards humanity as its goal. Parallels were drawn with the goal-directed process of embryological development, implying that the embryo recapitulates the history of life on earth. Even when naturalists realized that evolution was best represented as a branching tree rather than a ladder, the tree was given a central trunk pointing toward humanity, all other developments being mere side-branches. The claim that humanity is the goal of creation survived in various non-Darwinian theories of evolution in the late nineteenth century.

This introduction outlines a new interpretation of the history of the idea of progress, focusing on the transition from a goal-directed model to an open-ended view in which there can be multiple forms of improvement. Developments in thinking about the history of life on earth are used as a guide to wider changes in the perception of how progress can operate. Early ideas based on the chain of being saw humanity as the goal of biological evolution, just as the first theories of social progress saw it as the ascent of a linear hierarchy of steps towards a future paradise or utopia. Darwinism transformed evolutionism by introducing the image of a branching 'tree of life' with no single goal of progress. Parallels to this transformation can be seen in twentieth-century approaches to human history and predictions of multiple possible futures based on the unpredictability of technological innovations. Progress has become less clear-cut and more open to criticism by those who reject the utilitarian basis of technological advance.