Summary

Concept 16.1: All of Life Is Connected through Its Evolutionary History

• Phylogeny is the history of descent of organisms from their common ancestor. Groups of evolutionarily related species are represented as related branches in a phylogenetic tree.
• A group of species that consists of a common ancestor and all its evolutionary descendants is called a clade. Named clades and species are called taxa. Review Figure 16.1
• Homologies are similar traits that have been inherited from a common ancestor.
• A trait that is shared by two or more taxa and is derived through evolution from a common ancestral form is called a synapomorphy.
• Similar traits may occur among species that do not result from common ancestry. Convergent evolution and evolutionary reversals can give rise to such traits, which are called homoplasies. Review Figure 16.2

Concept 16.2: Phylogeny Can Be Reconstructed from Traits of Organisms

• Phylogenetic trees can be inferred from synapomorphies and using the parsimony principle. Review Figure 16.3 and ACTIVITY 16.1
• Sources of phylogenetic information include morphology, patterns of development, the fossil record, behavioral traits, and molecular traits such as DNA and protein sequences. Review ANIMATED TUTORIAL 16.1
• Phylogenetic trees can be inferred with maximum likelihood methods, which calculate the probability that a particular tree will have generated the observed data. Review ANIMATED TUTORIAL 16.2

Concept 16.3: Phylogeny Makes Biology Comparative and Predictive

• Phylogenetic trees are used to reconstruct past events. Review Figures 16.6 and 16.7
• Biologists can use phylogenetic trees to reconstruct ancestral states. Review Figure 16.8
• Phylogenetic trees are used to reveal convergent evolution. Review Figure 16.9
• Phylogenetic trees may include estimates of times of divergence of lineages determined by molecular clock analysis. Review Figures 16.10 and 16.11

Concept 16.4: Phylogeny Is the Basis of Biological Classification

• Taxonomists organize biological diversity on the basis of evolutionary history.
• Taxa in modern classifications are expected to be clades, or monophyletic groups. Paraphyletic and polyphyletic groups are not considered appropriate taxonomic units. Review Figure 16.12 and ACTIVITY 16.2
• Several sets of rules govern the use of scientific names, with the goal of providing unique and universal names for biological taxa.