An ancestral species and all its evolutionary descendants define a(n) ________.

• A. clade
• B. gene pool
• C. population
• D. ecosystem

Answer: (A)

Verified step by step guidance

1. Understand the key terms in the question: 'ancestral species' refers to a common ancestor, and 'evolutionary descendants' are all the species that have evolved from that ancestor.
2. Recall the definition of a clade: A clade is a group of organisms that includes an ancestral species and all of its descendants, forming a single branch on the tree of life.
3. Differentiate the other options: A 'gene pool' refers to the total genetic diversity within a population, a 'population' is a group of individuals of the same species living in a specific area, and an 'ecosystem' includes all living organisms and their physical environment in a particular area.
4. Match the definition of a clade to the description in the question: The question specifically asks for a term that includes both an ancestral species and all its evolutionary descendants, which aligns with the definition of a clade.
5. Conclude that the correct answer is 'clade' based on the alignment of the definition with the question's description.