Chapter 3 - Systematics & Phylogeny

Systematics

The scientific study of the diversity of organisms and their evolutionary relationships.

Phylogeny

The evolutionary history and pattern of descent of a species or group of organisms.

Linnaean Hierarchy

The traditional nested ranking system: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Binomial Nomenclature

The two-part scientific naming system consisting of Genus (capitalized) and specific epithet (lowercase), both italicized or underlined.

Phylogenetic Tree

A branching diagram representing a hypothesis about the evolutionary relationships among taxa.

Node (Branch Point)

A point on a phylogenetic tree representing the divergence of two evolutionary lineages from a common ancestor.

Sister Taxa

Groups of organisms that share an immediate common ancestor not shared by any other group.

Polytomy

A branch point on a phylogenetic tree from which more than two descendant groups emerge, indicating unresolved evolutionary relationships.

Rooted Tree

A phylogenetic tree containing a branch point representing the most recent common ancestor of all taxa in the tree.

Basal Taxon

A lineage that diverged early in the history of a group and remains on a branch that originates near the common ancestor.

Homology

Phenotypic or genetic similarities between organisms due to shared ancestry (e.g., tetrapod limb structure).

Analogy (Homoplasy)

Similar characteristics resulting from convergent evolution rather than shared ancestry (e.g., wings of birds and insects).

Convergent Evolution

The independent evolution of similar traits in different lineages as a result of adaptation to similar environments or ecological niches.

Cladistics

An approach to biological classification in which organisms are categorized based on shared derived characteristics (synapomorphies).

Monophyletic Group (Clade)

A group consisting of a common ancestor and all of its descendants.

Paraphyletic Group

A group consisting of a common ancestor and some, but not all, of its descendants.

Polyphyletic Group

A group that includes distantly related organisms but does not include their most recent common ancestor.

Shared Ancestral Character (Symplesiomorphy)

A trait that originated in an ancestor of the taxon and is shared beyond the specific clade being studied.

Shared Derived Character (Synapomorphy)

An evolutionary novelty unique to a particular clade, not present in the common ancestor of the broader group.

Ingroup

The primary group of taxa whose evolutionary relationships are being analyzed.

Outgroup

A species or group of species closely related to the ingroup but known to have diverged before it, used as a reference point.

Maximum Parsimony

The principle stating that the simplest explanation—requiring the fewest evolutionary events (trait changes)—is preferred when constructing trees.

Maximum Likelihood

A statistical method that uses probability models of molecular evolution to find the tree most likely to produce the observed DNA/protein data.

Molecular Clock

A method estimating the absolute time of evolutionary change based on the observation that certain genome regions evolve at roughly constant rates.