Study Guide Chapter 23 - Systematics, Phylogenies, and Comparative Biology Understand what a phylogeny represents. What is systematics? Explain why phenotypic similarity does not necessarily indicate close evolutionary relationship. Describe the difference between ancestral and derived similarities. Explain why only shared, derived characters indicate close evolutionary relationship. Understand how a cladogram is constructed. Differentiate among monophyletic, paraphyletic, and polyphyletic groups. Explain the meaning of the phylogenetic species concept and why it is controversial. Explain the importance of homoplasy for interpreting patterns of evolutionary change. Describe how phylogenetic trees can reveal the existence of homoplasy. Discuss how a phylogenetic tree can indicate the timing of species diversification. Discuss how phylogenetic analysis can help identify patterns of disease transmission.