What is the purpose of a phylogenetic tree?

The purpose of a phylogenetic tree is to show evolutionary relationships among various species or groups of organisms. These trees illustrate how different species are related through evolution, indicating their common ancestry and divergence over time. By reading a phylogenetic tree, one can track how species have evolved, adapt, and split from common ancestors, providing insights into the evolutionary history of life on Earth.

In contrast, classifying organisms by structure focuses more on morphology and physical characteristics, while identifying organisms from a key is often a simpler identification process that does not reflect evolutionary relationships. Describing anatomical functions pertains to how various body parts work, which is a different focus entirely from understanding evolutionary lineages. This makes the correct answer the one that directly addresses how species are interconnected through evolutionary history.