Key Question: How are different species related to each other?
Evolutionary Context: Relatedness is tied to how recently two species share a common ancestor.
Objective: Construct a phylogenetic tree to show how different species evolved from common ancestors using observable traits.
Phylogenetic Tree
Definition: A graphical representation showing the evolutionary relationships among various biological species based on similarities and differences in their physical or genetic characteristics.
Simplification: The example uses five species and five traits. In practice, biologists use numerous traits and molecular evidence (DNA/protein differences).
Origin of Term:
Phylo: Greek for group or kind.
Genetic: Related to genesis or origin.
Constructing a Phylogenetic Tree
Outgroup Identification
Lamprey is identified as an outgroup because it lacks the observable traits of the other species.
Purpose of Outgroup: Provides a reference point for determining the root of the tree.
Branching Point
Start with a common ancestor deep in the past.
The first divergence is between the lamprey and all other species.
Derived Traits
Jaws: Derived trait present in all species except the lamprey.
At some point, a species evolved jaws which proved to be favorable.
Further Divergence
Sea Bass: Next divergence after jaws; lacks lungs, unlike the remaining species.
Lungs: Hypothesized to have evolved in the ancestors of the antelope, bald eagle, and alligator.
Remaining Traits and Species
Gizzard: Present in bald eagle and alligator.
Feathers: Unique to the bald eagle, evolved after divergence from common ancestor with alligator.
Fur: Present in antelope, placement on the tree is less certain without further evidence.
Principle of Parsimony
Definition: Preference for the simplest explanation that fits the evidence.
Application: Applied to hypothesize the simplest evolutionary path for the traits considered.
Summary
Phylogenetic Tree Outcome: Provides a visual hypothesis of species relatedness and common ancestry.
Complexity and Evidence: Real phylogenetic studies incorporate genetic evidence to refine hypotheses.
Interpreting the Tree:
Bald eagle and alligator are more closely related to each other than to the antelope, based on more recent common ancestry.
Ongoing research and evidence gathering are necessary for tree refinement.
Future Considerations
Further Evidence: Look at genetic data and protein comparisons to support or refine the phylogenetic tree's accuracy.
Complex Hypotheses: Additional research may reveal more complex evolutionary explanations.