Carl Gustav Carus with a sketchbook facing the cliffs above a valley

Where does the individual begin for Carus?

Carl Gustav Carus (1789–1869) was a German physician, naturalist and landscape painter. A cliff face would have served him well to illustrate a question in Natur und Idee. You can break off a piece of rock and hold it up on its own. But where was its boundary before you broke it off? A crystal poses the question differently. Its faces may already show, within the surrounding rock, how far this particular body extends. For Carus the difference bears on what it means for a living creature to be an individual.

A shape within the mass

The first thing within the mass of the solid earth that foreshadows and prepares the way for the individual life of creatures later to inhabit its surface is the crystal.

– Carl Gustav Carus, Natur und Idee oder das Werdende und sein Gesetz, 1861, p. 178.[1]

Carus’s unusual German term Erdveste means the solid body of the Earth. His “epitelluric” creatures live on its surface. Across a single page he moves between three scales: the planet taken as a whole, a crystal within its mass, and the many individual beings that live on its surface. He assumes that the approach of organic life must already be discernible where the materials in view are still those of geology. The crystal earns its place here because its characteristic shape can be picked out.

What counts as one?

Carus recalls a difficulty he attributes to contemporary mineralogists. Examining the chemical constituents of a rock had yielded conflicting answers about what to count as a unit. A well-formed crystal offered something observers could point to together. At that point Carus takes a step beyond mineral description. The shape that a mineralogist can identify as a single specimen becomes, for him, an early intimation of individuality. The same crystal invites two quite distinct questions.