Unit #1 Flashcards
evolution
descent with modification
phylogenetic tree
A diagram that depicts the hypothetical phylogeny of the taxa under consideration.
The points at which lineages split represent ancestor taxa to the descendant taxa appearing at the
terminal points of the cladogram
node
represents a speciation event on the phylogenetic tree
internode
a line on phylogenetic tree connecting two speciation events and represents at least one
ancestral species.
Selection
Process which favors one feature of organisms in a population over another feature found in
the population. This occurs through differential reproduction - those with the favored feature produce
more offspring than those with the other feature, such that they become a greater percentage of the
population in the next generation.
Biological classification
The orderly arrangement of organisms in hierarchical system that ideally
reflects evolutionary history
Phylogeny
The evolutionary relationships among organisms; the patterns of lineage branching
produced by the true evolutionary history of the organisms being considered.
Systematics
Field of biology that deals with the diversity of life. Systematics is usually divided into the
two areas of phylogenetics and taxonomy
Taxon
Any named group of organisms, not necessarily a clade.
Taxonomy
The science of naming and classifying organisms.
Phylogenetics
Field of biology that deals with the relationships between organisms. It includes the
discovery of these relationships, and the study of the causes behind this pattern.
Clasdistics
organisms grouped strictly on homology. Trees are based on genealogy not simply similarity.
Ancestor
Any organism, population, or species from which some other organism, population, or species
is descended by reproduction
Character
Heritable trait possessed by an organism
Apomorphy
a derived character
Synapomorphy
a shared derived characteristic; used to infer ancestry and thus construct clades
Autapomorphy
a unique derived characteristic (not shared with any other taxon)
Plesiomorphy
an ancestral character state for the taxa under consideration
Symplesiomorphy
A ancestral character shared by the taxa under consideration
Character state
characters are usually described in terms of their states, for example: “hair present” vs.
“hair absent,” where “hair” is the character, and “present” and “absent” are its states
Ancestral
Describes a character state that is present in the common ancestor of a clade. An ancestral
character state is inferred to be the original condition of that character within the clade under
consideration.
Derived
Describes a character state that is present in one or more subclades, but not all, of a clade
under consideration. A derived character state is inferred to be a modified version of the primitive
condition of that character, and to have arisen later in the evolution of the clade. For example,
“presence of hair” is a primitive character state for all mammals, whereas the “hairlessness” of whales
is a derived state for one subclade within the Mammalia
Polarity of characters
The states of characters used in a cladistic analysis, either ancestral or derived.
Ancestral characters are those acquired by an ancestor deeper in the phylogeny than the most recent
common ancestor of the taxa under consideration. Derived characters are those acquired by the most
recent common ancestor of the taxa under consideration
Analog
A feature that appears similar in two taxa which have originated from two different ancestors.
Homoplasy
a character shared by a set of species but not present in their common ancestor
Homolog
A feature that appears similar in two or more taxa with a common ancestor that also
possessed that feature.
Homology
Two structures are considered homologous when they are inherited from a common
ancestor, which possessed the structure
Clade
A monophyletic taxon; a group of organisms which includes the most recent common ancestor of
all of its members and all of the descendants of that most recent common ancestor.
Cladogenesis
The development of a new clade; the splitting of a single lineage into two distinct
lineages; speciation.
Cladogram
A diagram, resulting from a cladistic analysis, which depicts a hypothetical branching
sequence of lineages leading to the taxa under consideration. The points of branching within a
cladogram are called nodes. All taxa occur at the endpoints of the cladogram.
Convergent evolution
an evolutionary change producing similar characteristics in two or more distantly
related forms because of their separate adaptation to common ecological conditions
Hypothesis
A concept or idea that can be falsified by various scientific methods.
Ingroup
In a cladistic analysis, the set of taxa which are hypothesized to be more closely related to
each other than any are to the outgroup.
Outgroup
- In a cladistic analysis, any taxon used to help resolve the polarity of characters, and which is
hypothesized to be less closely related to each of the taxa under consideration than any are to each
other.
Lineage
Any continuous line of descent; any series of organisms connected by reproduction by parent
of offspring
Monophyletic
Term applied to a group of organisms, which includes the most recent common ancestor
of all of its members and all of the descendants of that most recent common ancestor. A monophyletic
group is called a clade.
Paraphyletic
Term applied to a group of organisms, which includes the most recent common ancestor
of all of its members, but not all of the descendants of that most recent common ancestor.
Polyphyletic
Term applied to a group of organisms, which does not include the most recent common
ancestor of those organisms; the ancestor does not possess the character shared by members of the
group
Sister group
The two clades resulting from the splitting of a single lineage.
Parsimony
Refers to a rule used to choose among possible cladograms, which states that the cladogram implying the least number of changes in character states is the best.
