Changes that have transformed life from its earliest beginnings to the diversity that is present today - genetic change through time

Microevolution - change(s) in the gene pool of a population over a succession of generations

Macroevolution - evolutionary change on a grand scale - includes origin of novel designs, evolutionary trends, adaptive radiation & mass extinctions

Genetic drift - changes in gene pool of a small population due to chance

Gene flow - loss or gain of alleles due to immigration or emigration

Mutations - change in DNA of gene(s) - rare

Nonrandom mating - individuals mate more often with close neighbors than distant members

Natural Selection - differential success in reproduction - only mechanism that is adaptive

Stabilizing - culls extreme variants from population - tends to reduce variation and maintain "status quo"

Directional - favors variants of one extreme - shifts overall makeup of population in one direction

Diversifying - favors extreme variants over intermediates - can result in "balanced polymorphism"

From Latin - means "kind" or "appearance"

Biological species concept - emphasizes reproductive isolation - ".. Populations whose members actually or potentially interbreed, and are reproductively isolated from other such populations"

More difficult to define with organisms which reproduce asexually

Involves certain types of barriers that impede or prevent two species from producing viable, fertile offspring

Prezygotic barriers - impede mating or hinder fertilization if mating occurs - includes habitat, behavioral, temporal, mechanical, & gametic isolation

Postzygotic barriers - prevent viability of zygote if mating occurs - includes reduced hybrid viability and/or fertility, and hybrid breakdown

Morphological species - based on measurable physical characteristics

Recognition species - based on features that allow members to mate successfully

Cohesion species - mechanisms that maintain species as distinct entities

Ecological species - based on habitat and niche

Evolutionary species - sequence of ancestral and decendent populations evolving independently

The origin of new species

Anagenesis - also known as phyletic evolution - transformation of one species into another

Cladogenesis - also known as branching evolution - budding of one or more new species from a parent species that continues to exist

Allopatric - populations isolated by geographic barrier that blocks gene flow - e.g., mountain range(s) - ranges do not overlap

Sympatric - populations isolated by intrinsic factors that block gene flow - e.g., chromosomal changes or nonrandom mating - ranges overlap

Most evolutionary novelties are modified versions of older structures

Many macroevolutionary changes have been associated with genes that control development

Macroevolution not oriented toward goals - results from fact that species with certain characteristics speciate more often than others

Some changes so novel that new species originates new taxon