Art history is one of the undisputed, remarkable success stories of the humanities in the German-speaking countries. Scholars from Germany, Austria and Switzerland such as Aby Warburg, Erwin Panofsky, Alois Riegl and Heinrich Wölfflin instigated an approach that focused on a close reading of individual works of art but never lost sight of the larger social, cultural and philosophical context. In this tradition, ‘art’ potentially encompasses every entity that was created, touched or reshaped by human agency: industrial buildings, or natural objects moved to treasure chambers, or herbaria, can become the objects of art-historical and iconological study. One influential contemporary representative of this precise, but hardly ever boring, science of images, Bildwissenschaft, is Horst Bredekamp, professor of art history at the Humboldt University in Berlin. Bredekamp's mercurial interests have ranged from Renaissance art to the iconology of sports photography. It is thus not surprising that he has finally directed his analytic gaze towards Charles Darwin's visual arguments. In his concise and powerful, but in the end not entirely persuasive, study, Bredekamp examines the significance of the tree and coral analogies in Darwin's developing thinking about species change.

Bredekamp identifies Darwin's ‘Copernican moment’ with his use of stippled lines for extinct lineages and uninterrupted lines for extant lineages in his sketches in Notebook B. In this moment Darwin replaced the traditional tree models that illustrate static plans with an idea that emphasized the temporality of a process. That Darwin's sketches in Notebook B do not conform easily to the tree metaphor is well known. Bredekamp documents Darwin's continuing struggle with visual metaphors, including how he reacted to Hugh Strickland's cartographic model and Louis Agassiz's circular analogy. But in 1857 Darwin returned to the tree analogy; he recognized that Wallace had used this metaphor to good and convincing effect, and, Bredekamp claims, in order to defend a claim to priority, he started to present the image of the tree of life as his own idea.

Bredekamp appears to be disappointed that Darwin gave up on the coral. The coral is for Bredekamp an iconological concept that stands at the boundary of Naturphilosophie and modern biology. Darwin preserved the image of the polyps as diligent and patient creators of huge and beautiful structures. While tracing the symbolic and metaphorical functions of corals, Bredekamp's argument enters more uncertain ground. In his earlier study Antikensehnsucht und Maschinenglauben (Berlin, 1993), Bredekamp showed that in the treasure chambers of the sixteenth and seventeenth centuries corals were highly regarded items, and he claims that these organisms paved the way for evolutionary thinking. It is, though, highly questionable whether Darwin's diagrams can be traced back to the tradition of the Renaissance Kunstkammer. Julia Voss claims in her study Darwins Bilder (Frankfurt, 2007) that Darwin's visual strategy has to be understood against the background of the enormous number of specimens that were collected and stored in the imperial museums. It was no longer the unique and beautiful exemplar that was of interest. The vast and indiscriminate shipments arriving from all over the world drew attention to the variability of species and, according to Voss, Darwin's visual strategy developed to represent time, change, variability and diversity. I agree with Voss's conclusion, but one of the major achievements of Bredekamp's study is to draw attention to the independent life and contested nature of scientific imagery. The contemporary discourse of evolutionary biology is wholly dominated by the metaphor of the tree of life. In the nineteenth century, biology struggled over its visual metaphors and representations, over the appropriateness of trees, corals, nets, circles or maps. The full significance of these images could, according to Bredekamp, never be fully captured by words; images are not derivative and incidental, but active bearers of thought. Furthermore, he suggests that the struggle over visual metaphors for the order and history of life was one of the creative highlights of pre-Darwinian biology, and that contemporary evolutionary biology is regrettably impoverished with respect to its imagery. Ernst Haeckel is, by Bredekamp's lights, largely responsible for this state of affairs; he accuses the influential German biologist of having transformed Darwin's abstract and exploratory drawings into the mimetic image of the oak, with its central dominating stem. This represents the displacement of metaphors and visual concepts that acknowledge nature's anarchic diversity by one that emphasizes a harmonized and progressive order.

Haeckel's orderly nature did not require human agency to turn it into art – nature, for him, was equipped with its own artistic drive, Kunsttrieb. Olaf Breidbach's sumptuously illustrated volume bears impressive witness to Ernst Haeckel's concept of natural aesthetics. Next to a wealth of hand-drawn natural forms, the volume also contains remarkable photographs of Haeckel's ‘Villa Medusa’ in Jena, which was designed in its entirety according to evolutionary aesthetic principles. Breidbach skilfully situates Haeckel's aesthetic project in the artistic environment of the time. Alois Riegl's theory of ornament, William Morris's arts and crafts movement, and the science fiction of Camille Flammarion serve as background and context to Haeckel's aesthetic and scientific project. Breidbach's study is an examination of Haeckel's visual heritage and thus does not endeavour to engage in depth with the more controversial topics surrounding Haeckel and his theories. Still, it would perhaps have been possible to investigate the connection between the exaggerated, idealized order and symmetry of Haeckel's drawings and his ideas about the order of the natural, social and political world.

How pioneering are these studies that elevate pictorial representations to a far more central place in the development and justification of scientific theories? Certain strands in cognitive science have argued for a long time that human thought emerges from embodied activity. Cognition is not purely internal to the brain, symbolic and computational, but shaped by embodied action. Diagrams and images are more than mere means of persuasion. Drawing and beholding images can be considered as thinking with the body and the senses. What these studies show is that the histories of art, of science and of culture can enter into a fruitful exchange. The philosophy of the (embodied) mind could be a useful participant as well.