Rucete ✏ Campbell Biology In a Nutshell
Unit 5 THE EVOLUTIONARY HISTORY OF BIOLOGICAL DIVERSITY — Concept 26.1 Phylogenies Show Evolutionary Relationships
Phylogenies are evolutionary trees that depict the relationships among species or groups based on shared ancestry. Systematists construct these trees using morphological and molecular data to understand the branching history of life.
Binomial Nomenclature and Classification
Binomial nomenclature (developed by Linnaeus) gives each species a two-part Latin name:
Genus name (capitalized) + specific epithet (lowercase), both italicized (e.g., Panthera pardus).
Linnaeus also introduced a hierarchical classification system:
Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species.
Each level is called a taxon; broader taxa group species based on shared characteristics.
Linking Classification and Phylogeny
A phylogenetic tree represents a hypothesis of evolutionary relationships.
Trees are constructed by identifying shared ancestry and branching patterns among species.
Misclassifications may occur if classification is based on traits lost or gained over time rather than true evolutionary relationships.
Modern classification often aims to reflect monophyletic groups—a common ancestor and all its descendants.
Reading Phylogenetic Trees
Branch points (nodes) represent common ancestors.
Sister taxa are groups that share an immediate common ancestor.
Trees can be drawn in different orientations (vertical, horizontal, diagonal), but the relationships stay the same.
Rotating branches around nodes does not change the evolutionary information.
Important principles when interpreting phylogenies:
Trees show patterns of descent, not direct ancestry (e.g., humans didn’t evolve from chimps—they share a common ancestor).
Branch length usually does not indicate time unless specified.
Taxa at the tips have all evolved for the same amount of time from a common ancestor.
Practical Applications of Phylogenies
Agriculture: Phylogenies help identify wild relatives of crops (e.g., maize) that may offer beneficial traits for breeding.
Conservation and forensics: Genetic trees can identify illegally harvested species (e.g., whale meat identification using mtDNA).
Phylogenies assist in understanding evolutionary trends, tracing gene family origins, and clarifying species boundaries.
Homology vs. Analogy
Homology: Similarity due to shared ancestry (e.g., vertebrate limbs, shared gene sequences).
Analogy: Similarity due to convergent evolution, where unrelated organisms evolve similar traits due to similar environmental pressures.
Example: Australian marsupial mole vs. African golden mole—similar features but not closely related.
Sorting Homology from Analogy
Complex structures or gene sequences that are highly similar are more likely homologous.
Superficial similarities (e.g., body shape) can be misleading if they result from convergence, not shared ancestry.
Accurate phylogenies require distinguishing between homology and analogy using detailed morphological or molecular data.
In a Nutshell
Phylogenetic trees are powerful tools for visualizing evolutionary relationships. They are based on shared ancestry, not appearance, and must distinguish between homology and analogy. These trees are essential for modern biology, guiding classification, conservation, and our understanding of biodiversity.