Phylogeny and the Tree of Life 🌳

• Binomial Nomenclature

Two-part scientific naming system: Genus (capitalized) + species (lowercase, italicized), e.g., Homo sapiens.

• Linnaeus’ Classical Hierarchy

Organisms classified by physical traits into nested groups (kingdom → species).

• Modern Phylogeny

Uses molecular (DNA, RNA, proteins) and morphological data to show evolutionary relationships based on ancestry.

• Historical Categorization

Aristotle grouped organisms by complexity; Linnaeus used morphology without evolutionary context.

• Rooted Tree

Shows a single common ancestor at the base.

• Unrooted Tree

Displays relationships without indicating ancestry direction.

• Diagonal/Vertical Trees

Different visual layouts of relationships; diagonal often simpler, vertical emphasizes hierarchy.

• Cladogram

Branching diagram showing evolutionary relationships based on shared traits, without time scale.

• Phylogram

Tree with branch lengths proportional to genetic change.

• Parsimony Principle

The simplest explanation (fewest evolutionary changes) is preferred when building phylogenetic trees.

• Node

Represents a common ancestor.

• Branch

Represents a lineage.

• Sister Group

Two lineages that share an immediate common ancestor.

• Clade

Group of organisms including an ancestor and all its descendants (monophyletic).

• Outgroup

A lineage outside the group of interest, used for comparison.

• Ingroup

The group of organisms being studied.

• Monophyletic

Includes ancestor and all descendants.

• Paraphyletic

Includes ancestor but not all descendants.

• Polyphyletic

Group formed from unrelated lineages, excluding common ancestor.

• Extinct Taxa

Lineages that no longer exist.

• Extant Taxa

Lineages that are still living.

• Divergent Evolution

Lineages split and evolve different traits from a common ancestor.

• Convergent Evolution

Different lineages evolve similar traits independently due to similar environments.

• Phylogeny

Graphical hypothesis of evolutionary relationships; includes cladograms, phylograms, dendrograms.