A.3.2 Classification and cladistics

kingdom

second highest taxonomic rank, below domain; the largest and most inclusive grouping

domain

the highest taxonomic rank in the hierarchical biological classification system, above the kingdom level; there are three sections of life: archaea, eubacteria, eukarya

cladistics

classification system used to construct evolutionary trees; organisms are categorized based on shared derived characteristics that can be traced to a group’s most recent common ancestor and are not present in more distant ancestors; characteristics can be anatomical, physiological, behavioural, or genetic and protein sequences

clade

a group of organisms that have evolved from a common ancestor

cladogram

a diagram, used in cladistics, that shows evolutionary relations among organisms

molecular clock

a measure of evolutionary change over time based on the mutation rate of DNA sequences, or the proteins they encode; can be used for estimating how long ago two related organisms diverged from a common ancestor

node

a branching point from the ancestral population in a cladogram; it represents a speciation event

terminal branch

indicates both extinct and extant species in a cladogram, leading to a terminal node

terminal node

represents the hypothetical last common ancestral interbreeding population of the taxon labelled at the tip of a cladogram

root

the central trunk of a cladogram, indicating a common ancestor to all groups that branch from it

evidence for evolution

palaeontology (study of fossils)

comparative biochemistry (nucleic acids)

comparative embryology (development of organisms)

comparative anatomy (structural features)

phylum

organisms constructed on a similar plan

class

a grouping of orders within a phylum

order

a group of apparently related families

family

a group of apparently related genera

genus

a group of similar and closely related species

species

a group of organisms capable of interbreeding to produce fertile offspring