Evidence of Evolution and Systematics

Speciation that occurs when geographic barriers isolate populations and prevent gene flow Allopatric speciation often leads to adaptive radiation as populations adapt to new environments.

New species arise within the area of parent populations without geographic barriers This can occur through genetic isolation mechanisms.

A chromosomal change that occurs in plants, causing chromosome numbers to multiply in some individuals

Reproductive barriers that impede mating between species, including: * Habitat * Temporal * Behavioral * Mechanical * Gametic

Reproductive barriers that prevent hybrid zygotes from developing into viable, fertile adults, including: * Hybrid infertility * Reduced viability

A region in which members of different species meet and mate Can lead to reinforcement, fusion, or stability of reproductive barriers.

The disappearance of species from Earth, generally occurring gradually Humans are influencing the rate of extinction.

The geographical distribution of species, indicating modern species evolve from ancestors in those regions

Preserved evidence of organisms that confirms the existence of earlier species

A method that tells the order in which groups of species were present in a sequence of strata

Fossils that permit the relative dating of rocks within a narrow time span, such as trilobites

Dating that provides the age of fossils in years, often using radiometric dating methods

The similar stages in embryonic development of closely related organisms, establishing homology

Similarity resulting from common ancestry

Similarity not resulting from common ancestry

Structures that have lost their function over evolutionary time

Evolutionary relationships among species are reflected in their DNA

When two species originate from a common ancestor and contain homologous structures

When two unrelated species evolve similar traits, containing analogous structures

When two species with a common ancestry evolve similar traits independently

The evolution of one species due to the evolution of another species

A model where species diverge in spurts of relatively rapid change, with long periods of stasis

Evolution that occurs by the gradual accumulation of small changes

The evolutionary history of a species or a group of related species