Chapter 26: Phylogeny and the Tree of Life

Comprehensive vocabulary flashcards covering Chapter 26 on phylogeny, cladistics, character evolution, phylogenetic reconstruction, and the tree of life.

Systematics

The scientific discipline concerned with studying the diversity of organisms and reconstructing their evolutionary relationships through time using fossil, molecular, and genetic data.

Taxonomy

The scientific discipline concerned with the identification, description, naming, and hierarchical classification of organisms.

Cladogram

A branching diagram depicting the evolutionary history and phylogenetic relationships among groups of related species.

Carolus Linnaeus

The 18th-century Swedish naturalist who published Systema Naturae, introducing a hierarchical classification system based on structural resemblances and binomial nomenclature.

Binomial nomenclature

The standard two-part naming system for identifying a species, consisting of the genus name followed by the specific epithet.

Genus

The first part of a binomial scientific name; it is capitalized, written in italics, and groups one or more closely related species together.

Specific epithet

The second part of a binomial scientific name; it is written in lowercase and italics, unique to a specific species within a genus, and cannot stand alone as the species name.

Taxon

A named taxonomic unit at any designated level of the biological classification hierarchy (plural: taxa).

Hierarchical classification

The Linnaean system of organizing organisms into increasingly broad and inclusive categorical ranks, from species up to domain.

Linnaean taxonomic ranks

The progressive sequence of biological classification levels: species, genus, family, order, class, phylum, kingdom, and domain.

Non-equivalence of taxonomic ranks

The principle that taxa placed at the same formal rank in different lineages do not represent equivalent amounts of genetic diversity or evolutionary age (e.g., an order of snails has less genetic diversity than an order of mammals).

PhyloCode

A proposed systematic protocol that designates only groups that include an ancestor and all of its evolutionary descendants as taxonomically valid clades.

Node (Branch point)

A divergence point on a phylogenetic tree that represents the hypothetical most recent common ancestor of the descendant lineages that branch from it.

Sister taxa

Groups of organisms that share an immediate common ancestor not shared by any other group, making them each other's closest relatives on a phylogenetic tree.

Rooted tree

A phylogenetic tree that contains a branch point representing the most recent common ancestor of all the taxa shown in the diagram.

Basal taxon

A lineage that diverges early in the evolutionary history of a group and originates near the common ancestor of that entire group.

Polytomy

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

Pattern of descent

The evolutionary lineage pathways depicted by phylogenetic trees, which illustrate ancestral relationships rather than overall phenotypic similarity.

Cladistics

A method of biological classification and phylogenetic analysis that uses shared characters (traits) to generate hypotheses of evolutionary relationships.

Clade

A monophyletic group consisting of a common ancestral species and all of its evolutionary descendants.

Monophyletic group

A natural phylogenetic grouping that consists of an ancestral species and all of its descendants.

Paraphyletic group

An unnatural phylogenetic grouping consisting of an ancestral species and some, but not all, of its evolutionary descendants.

Polyphyletic group

An unnatural grouping consisting of various species derived from different ancestral lineages, omitting the most recent common ancestor of all members.

Synapomorphy

A shared derived character; an evolutionary novelty unique to a particular clade that diagnoses and defines that monophyletic group.

Symplesiomorphy

A shared ancestral character; a trait that originated in an ancestor prior to the common ancestor of the specific clade being analyzed.

Autapomorphy

A self-derived character that appears on only a single terminal branch of a particular tree, not shared with other taxa, making it uninformative for uniting lineages on that tree.

Derived character

An evolutionary trait that has changed from the ancestral state observed in previous ancestors.

Ancestral character

A trait that originated in an earlier ancestor and is retained in an unmodified state in descendant lineages.

Ingroup

The focal species or group of species whose evolutionary relationships are being actively reconstructed and studied.

Outgroup

A species or group of species closely related to the ingroup that diverged before the ingroup's lineage, used to polarize characters into ancestral and derived states.

Character polarity

The established direction of evolutionary character transformation, distinguishing whether a character state is ancestral or derived within an ingroup.

Character-taxon matrix

A systematic scoring table where taxa are compared across evaluated characters, traditionally coding the ancestral outgroup as 0 and derived states as 1.

Maximum parsimony

A phylogenetic principle asserting that the tree requiring the fewest evolutionary changes (shortest number of steps) is the most well-supported hypothesis.

Maximum likelihood

A statistical phylogenetic method that identifies the tree topology reflecting the most probable sequence of evolutionary events under the assumption of a constant rate of DNA change.

Chronological branch length

A phylogenetic tree branch metric where the length of a branch represents absolute geologic time elapsed since divergence from the nearest relative, calibrated using the fossil record.

Genetic branch length

A phylogenetic tree branch metric where the length of a branch is proportional to the number of genetic changes, such as nucleotide substitutions, accumulated in that lineage.

Phylogenetic bracketing

A predictive approach that infers unknown behavioral, physiological, or anatomical characteristics of an extinct ancestor based on features shared by its living descendants.

Ribosomal RNA (rRNA) gene sequencing

Molecular sequencing of DNA coding for ribosomal RNA, which evolves relatively slowly and is useful for investigating deep-time evolutionary divergences spanning hundreds of millions to billions of years.

Mitochondrial DNA (mtDNA) sequencing

Molecular sequencing of mitochondrial genetic material, which evolves rapidly and is useful for resolving recent evolutionary events, such as the divergence of human populations over thousands of years.

Orthologous genes

Homologous genes found in a single copy within a genome that diverge only after a speciation event occurs.

Paralogous genes

Homologous genes that originate from gene duplication events within a genome, which can diverge within a species and acquire novel functions to form gene families.

Gene family

A group of multiple related genes within an organism's genome that arose through repeated cycles of duplication and divergence (paralogs).

Genomic complexity paradox

The observation that the total number of genes in an organism is not strongly linked to its phenotypic complexity (e.g., humans have only about four times as many genes as unicellular yeast).

Neutral theory

The evolutionary theory stating that the majority of mutational changes in genes and proteins have no effect on fitness, are not influenced by natural selection, and occur at a predictable, regular rate.

Molecular clock

A method that estimates the absolute time of evolutionary divergence based on the assumption that nucleotide substitutions or amino acid mutations accumulate at a constant rate over time.

Molecular clock calibration

The procedure of plotting accumulated mutations against divergence dates known from the fossil record to determine the rate of molecular change over time.

Five-kingdom system

The historical mid-20th-century taxonomic scheme that organized life into Monera (prokaryotes), Protista, Plantae, Fungi, and Animalia.

Three-domain system

The modern phylogenetic framework supported by rRNA sequencing that classifies all life into three primary domains: Bacteria, Archaea, and Eukarya.

Horizontal gene transfer (HGT)

The lateral movement of genetic information between genomes of unrelated organisms via transposable elements, viral infection, plasmids, or cellular fusion.

Ring of life

A phylogenetic hypothesis proposing that eukaryotes originated from an ancient fusion or endosymbiotic relationship between a bacterium and an archaeon rather than through standard bifurcating branching.