Politics of recapitulation. Embryology offered a tool for understanding species as well as individual history. The doctrine of recapitulation held that embryos of higher species pass in their development through the adult forms of lower animals. Though not intended literally—the argument was for an underlying and ideal similarity—this view became increasingly influential. But the claim that animals could climb the developmental ladder provided subversive analogy for democratic politics. In 1820s and ’30s Britain this zoological philosophy was mobilized in the reform campaign of radical lecturers in the London medical schools. The established royal medical colleges used Cuvier’s anatomy and von Baer’s embryology against recapitulation and the idea that all animals were built on a common plan. The reformers eventually won, but later biologists incorporated perspectives from both sides.

Histories of development

Deeper studies of the development of the chick in the egg produced new principles of organization.

After the Napoleonic wars and the first wave of Romantic enthusiasm, the egg lost some symbolic value but gained in empirical interest. At the Bavarian University of Würzburg around 1816, two medical students from the German-speaking Baltic, Christian Pander and Karl Ernst von Baer, took a fresh look at the chick egg, the classical object of study since Aristotle. Pander went first because this banker’s son could afford high-quality engravings and to have an assistant incubate thousands of eggs. Opening these at different times and examining their contents under a magnifying glass, Pander argued that development began, not directly with organ formation, but with the organization of sheets of tissue, or germ layers.

The noble but impoverished von Baer had to wait for an academic post in Königsberg (now Kaliningrad) before he could extend Pander’s research, and even then endured many a sleepless night minding the incubator. In 1828, like the French comparative anatomist Georges Cuvier, von Baer influentially opposed the arrangement of the animal kingdom into a linear series and divided it instead into four separate types. Within each of them, development did not run in parallel but rather diverged.

Artificial incubator, 1834

 

Von Baer’s ideal figures of development, 1828

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