Which concept asserts the "fixity of species" as an idea in natural history?

The concept that asserts the "fixity of species" holds that species are unchanging and were created in their current forms, typically referencing a view in natural history that aligns with religious or creationist beliefs. This idea posits that species are static and have not undergone any modifications since their creation. This perspective was prevalent prior to the acceptance of evolutionary theory, which introduced the notion that species can adapt and change over time.

In contrast, the belief in the ability of species to evolve and adapt (the first choice) directly opposes the concept of fixity. The theory of natural selection and the notion of adaptive radiation both highlight the dynamic nature of species and their ability to change in response to environmental pressures, further demonstrating an evolutionary approach rather than a fixed standpoint. Thus, the correct answer encapsulates the traditional view that stands in stark contrast to contemporary understanding in evolutionary biology.