Adaptive Radiation rapid speciation after new characters arise (e.g., photosynthesis, flight), a new habitat is occupied (e.g., terrestrial), a new area is colonized (oceanic islands), or following mass extinctions.
Character Displacement variation of traits due to the presence of competing species. Example, three species of finches have different beak sizes on 4 different islands (A-D) where the other species are present (Lack, 1947).
Cladogenesis the formation of lineages (phylogenies) through progressive speciation, diversification, and extinction. The vertical axis is time and the horizontal axis is the range of a trait.
Convergence the formation of similar organs, structures, or morphology in response to selection pressures. Example, penguins, ichthyosaurs, dolphins.
Directional Selection process by which one state or value of a trait becomes more common in a population.
Disruptive (Diversifying) Selection process by which more than one trait of a population is selected, possibly leading to two different species.
Founder Event dispersal of a few individuals of a population, with only a small portion of the genetic diversity of the population, potentially resulting in speciation.
Gradualistic Evolution cladogenisis characterized by gradual changes in the frequency of traits in a population, sometimes leading to speciation.
ex. Dinos
Inversion A chromosomal mutation caused by the reversal of the genetic sequence in a chromosome. A barrier to reproduction with organisms with normal (non-inversion) chromosome because it inhibits the pairing of homologous chromosomes during fertilization and meiosis.
Phyletic Speciation speciation through time, without branching via. directional selection. "d e f" and "i j k" are series of plyletic species. The vertical axis is time & the horizontal axis is a trait.
Punctuated Equilibrium evolution (cladogenisis) characterized by speciation events (punctuation) and otherwise, relatively few changes in traits (stasis).
Reticulate Evolution evolution (cladogenisis) characterized by occasional hybridization and combination of two species.
Selection Pressure the environmental force altering the frequency of traits in a population. The S+ selective pressure is stronger than the S+ pressure, so its trait becomes more common. Selection may be for or against (S-) traits.
Stabelizing Selection process by which extreme traits of a population are elimintated.
Trait any physical characteristic of an organism: size, color, life-span. The blue curve represents the frequency (vertical axis) of a range of traits (horizontal axis) in a population.
Translocation A chromosomal mutation caused by the exchange of genetic material among non-homologous chromosomes. A barrier to reproduction with organisms with normal (non-inversion) chromosome because it inhibits the pairing of homologous chromosomes during fertilization and meiosis.
Vicariant Event historical appearance of a barrier* to genetic exchange, which separates a population, potentially resulting in speciation.
*river, mountain, desert etc. where the population cannot exist
Lack, D. 1947. Darwin's finches. Cambridge Univ. Press.


  • fitness: the reproductive success of an organism.

  • gradualism: macroevolution resulting from small microevolutionary changes over very long time periods.

  • mass extinction: a significant and abrupt increase in the rate of extinction above the background level. Example, the Permian, and the Cretaceous mass extinctions.