18.2 Modern Evolutionary Classification

1. 18.2 Modern Evolutionary Classification • Which similarities are most important? • Evolutionary classification • Classification using cladograms • Similarities in DNA and RNA • Molecular clocks

2. Which similarities are most important? • Based on how Linnaeus grouped organisms (physical characteristics), it would be difficult to determine which characteristics you base their name off of. • For example, would he group dolphins with fish because they live in water and have fins, or would they be mammals because they breath air and feed their young milk?

3. Evolutionary Classification • Phylogeny: the study of evolutionary relationships among organisms, Darwin gave rise to this study. • Biologists now group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities. • Evolutionary classification: the strategy of grouping organisms together based on their evolutionary history.

5. Classification Using Cladograms • Cladistic analysis: identifies and considers only those characteristics of organisms that are evolutionary innovations • Derived characters: characteristics that appear in recent parts of a lineage but not in its older members. • Cladogram: a diagram that shows the evolutionary relationships among a group of organisms.

6. Cladograms, cont. • They are useful tools that help scientists understand how one lineage branched from another in the course of evolution, kind of like a family tree.

7. Similarities in DNA and RNA • The genes of many organisms show important similarities at the molecular level. Similarities in DNA can be used to help determine classification and evolutionary relationships. • The more similar the DNA sequence in two species, the more recently they had a common ancestor.

8. Molecular Clocks • Molecular clock: uses DNA comparisons to estimate the length of time that two species have been evolving independently. • This process relies on mutations that occur. • The degree of dissimilarities is an indication of how long ago species shared a common ancestor. • This process can be difficult because each genome contains more than one “clock” because of the many different genes.