In an evolutionary tree depicting species 1 through 9, what does the common ancestor of all these species represent?

• A. A branch that leads only to species 1
• B. The most recent node from which all species 1-9 descend
• C. A modern species unrelated to species 1-9
• D. A species that evolved after species 1-9

Answer: (B)

Verified step by step guidance

1. Understand the concept of an evolutionary tree: An evolutionary tree (or phylogenetic tree) is a diagram that represents evolutionary relationships among species. Each branch point (node) represents a common ancestor shared by the species that diverge from that point.
2. Identify the common ancestor: The common ancestor of all species in the tree is the most recent node from which all species (in this case, species 1 through 9) descend. This node represents a shared evolutionary origin.
3. Eliminate incorrect options: A branch leading only to species 1 cannot represent the common ancestor of all species 1-9, as it pertains only to species 1. Similarly, a modern species unrelated to species 1-9 cannot be the common ancestor, as it does not share evolutionary lineage with them. Lastly, a species that evolved after species 1-9 cannot be their common ancestor, as it would have appeared later in time.
4. Focus on the correct interpretation: The correct answer is the most recent node from which all species 1-9 descend. This node represents the last shared ancestor before the species diverged into their respective evolutionary paths.
5. Relate to broader concepts: This question highlights the importance of understanding how evolutionary trees depict relationships and the concept of shared ancestry, which is fundamental to evolutionary biology.