bio keystones

SPECIES

A group of similar organisms that can breed and produce fertile offspring.

VARIATION

The range of possibilities for a trait; any phenotype within that range.

EVOLUTION

The change in species over time.

NATURAL SELECTION

The process by which organisms with variations that are favorable in their environment survive and reproduce passing those variations on to the next generation.

ADAPTATION

A trait that increases an organism's chance of survival and becomes more common in a population through natural selection.

POPULATION

All the members of single species that share the same environment.

FITNESS

The ability of an organism to survive and reproduce in its environment.

GENE POOL

All the alleles carried by members of a population, whether or not they are expressed.

ALLELE FREQUENCY

The ratio of a particular allele for a gene to all alleles for that gene in a population.

FOSSIL

The remains or traces of an organism that lived in a past age.

EXTINCTION

The permanent loss of a species.

BIODIVERSITY

The variety of organisms living on Earth or in a specific area, as indicated by the number of species.

SPECIATION

The formation of one or more new species from an existing species.

GENE MIGRATION

The transfer of alleles from one population into the gene pool of another (also called gene flow).

ISOLATING MECHANISM

Any characteristic that prevents successful breeding between species.

GENETIC DRIFT

A change in a population's gene pool as a result of chance events.

FOUNDER EFFECT

The loss of genetic variation that occurs when a very small number of individuals leave a large population and start a new one.

PHYLOGENETIC TREE

A diagram that shows the development of groups of organisms from a common ancestor.

GRADUALISM

The idea that evolutionary change occurs slowly and steadily over a long period of time.

PUNCTUATED EQUILIBRIUM

The idea that evolution occurs in spurts of rapid speciation between periods of little change.

HYPOTHESIS

A proposed, testable explanation for an observable aspect of the natural world, a possible answer to a testable scientific question.

THEORY

A well-tested and highly reliable explanation of some aspect of a natural phenomenon.

LAW OF SUPERPOSITION

A scientific law stating that, in undisturbed layers of sedimentary rock, young layers lie above older layers.

LAW

{Scientific} A generalized rule about a natural phenomenon, based on a large body of observations and having no observed exceptions.

HOMOLOGOUS STRUCTURES

Similar physical structures in different organisms that share a common ancestor.

ANALOGOUS STRUCTURES

Physical structures that have similar functions in different organisms but DIFFERENT forms of ancestry.

VESTIGIAL STRUCTURES

A physical structure that does not seem to play a major role in an organism's life functions but was more important in the organism's ancestors.

EMBRYOLOGY

The study of embryos.

EMBRYO

An early stage in the development of an organism.

ENDOSYMBIOSIS

A theorized process by which eukaryotic cells evolved from prokaryotes.