Darwin, Archaeopteryx lithographica and the Problem of Intermediate Species

This chapter explores Darwin’s conception of transitional forms and challenges his view on the problem of intermediate species. Starting with a brief historical introduction to the epistemological status of fossils before Darwin’s time, I proceed to the analysis of Darwin’s theory of evolution and identify three fundamental hypotheses that substantially influence his investigation of the fossil record. Although Darwin’s theory implies the necessary existence of transitional forms, he believes that the paleontological record remains incomplete due to lacking discovery of intermediate forms. I find several reasons for such a radical conclusion. I deconstruct his specific yet ambiguous conception of intermediate forms and show that, in addition to the fundamental assumptions of his theory, this conception is at the root of the emergence of the intermediate species problem. Further, I explicate how this problem arises at two distinct but connected levels of Darwin’s theory. Whilst at the first level it appears in the form of a vague interpretation of the intermediate form concept, at the second level this problem takes a form of a stringent requirement for classification of an organism as an intermediate form: the discovery of a complete chain of transitional forms that connects such an organism to at least one known species. Archaeopteryx lithographica could not satisfy such a requirement; actually, no organic form can. The problem of the intermediate species thus remains one of ‘the gravest difficulties’ for Darwin’s theory of evolution.