Final answer:
In the context of the feature comparison model of concepts, a defining feature is a feature shared by all members of a concept category, as seen in cladistics within biology. The answer to the presented question is option a), which indicates this shared nature of a defining feature.
Step-by-step explanation:
According to the feature comparison model of concepts, a defining feature can be understood in the context of classifications within biology, particularly when it comes to identifying species or groups in cladistics. A defining feature is:
a) A feature shared by all members of a concept category. This feature would be considered a shared ancestral character because it is present in all members of a clade, not showing variation or evolution within the group. Cladistics particularly values shared derived traits, which are features that some organisms have and others do not, revealing evolutionary relationships within the clade. The presence of an amniotic egg is an example of a shared derived trait because it highlights common ancestry among certain groups that possess this characteristic, distinguishing them from other related species that lack this trait.
Therefore, the correct answer to the question provided is option a), which states that a defining feature is a feature shared by all members of a concept category in the context of the feature comparison model of concepts.