In a comparison of birds and mammals, the condition of having four limbs is a. a shared ancestral character. b. a shared derived character. c. a character useful for distinguishing birds from mammals. d. an example of analogy rather than homology.

Key Concepts

Homology vs. Analogy

Homology refers to traits inherited from a common ancestor, while analogy describes traits that arise independently due to similar environmental pressures, not shared ancestry. In the context of limbs in birds and mammals, the four-limb structure is homologous, as both groups descended from a common vertebrate ancestor.

Shared Ancestral Characters

A shared ancestral character is a trait that originated in a common ancestor and is present in all its descendants. In this case, the presence of four limbs is a shared ancestral character for both birds and mammals, as they both evolved from tetrapod ancestors.

Shared Derived Characters

A shared derived character is a trait that is present in an organism but absent in its distant ancestors. This concept is crucial for distinguishing between groups; however, the four-limb condition is not a derived character for birds and mammals, as it predates their divergence.