Final answer:
The primary idea behind the Pre-Darwinian Complex or the typological species concept was that species were considered static and unchanging, based on the writings of Plato. Each species was believed to have a fixed essence or set of characteristics that defined it.
Step-by-step explanation:
The primary idea behind the Pre-Darwinian Complex or the typological species concept, prevalent before Charles Darwin's theory of evolution, was that species were considered static and unchanging. This concept was grounded in the writings of Plato, who believed that species had fixed forms or ideal types. It was thought that each species had an essence or set of characteristics that defined it and that these characteristics were uniform across all members of the species. The typological species concept emphasized the classification and categorization of organisms based on their perceived similarities and differences.