I must say I am quite impressed by the uncovering through reading The Structure of Evolutionary Theory of the way that Darwin has treated historical and fossil research. In a sense Darwin uses a technique very similar to the way that Astronomers use in order to uncover the history and evolution of stars. Since the lifetime of a star is incredibly larger than the time scale of a human life astronomers use ’snapshots’ of stars that are currently available, which they know that have the same age (globular clusters), and draw their differences in evolution depending on their mass and luminocity thus plotting the famous Hertzsprung-Russell diagram.
Darwin understands the massive gaps in historical evidence and fossils and uses the present state of organisms around various parts of the world in order to plot a snapshot of evolution, as an aid in the Evolutionary theory argument.
The abstraction involved in this is rather amazing.
(page 106)