Acclimatization

The manner in which an organism adjusts to changes in altitude or climate (somewhat similar to adaptation).

Adaptation

An alteration or adjustment by which a species or individual improves its condition in relationship to its environment.

Adaptive Radiation

The relatively rapid evolution of many species from a single species that generally occurs when colonizers reach geographically remote areas

Algae

A plantlike organism of any of several phyla, divisions, or classes of chiefly aquatic usually chlorophyll-containing nonvascular organisms of polyphyletic origin that usually include the green, yellow-green, brown, and red algae in the eukaryotes and the blue-green algae in the prokaryotes.

Allele

One of a pair or series of alternative forms of a gene occupying the same locus in homologous chromosomes.

Allelic Frequency

The relative occurrence of an allele within a given population or gene pool.

Altruism

Behavior of an individual that directly benefits other members of a population.

Amphibian

Any animal with scaleless skin that lives its life both on water and on land.

Anatomy

The structure of the body of living things.

Aneuploidy

A loss or gain of part of a set of chromosomes.

Analogous Structure

A body part of one species that resembles or serves the same function as a body part of a different species because both structures evolved independently as similar adaptations to their environments.

Allopolyploid

Polyploid that is formed via sexual reproduction.

Allo-parapatric Speciation

The formation of a new species that occurs when populations are initially separated, as in allopatric speciation, but then are united, allowing parapatric speciation to finish the separation process.

Allopatric Speciation

The formation of new species due to a geographic barrier which divides an existing species into two or more smaller populations so that interbreeding between the resulting populations is prevented. Also known as Geographical Speciation.

Archaebacteria

A categorization of bacteria typically found in unusual environments and distinguished from the rest of the prokaryotes by several criteria, including the number of ribosomal proteins and the lack of muramic acid in cell walls. Commonly known as Archaeobacteria.

Archeozoic Era

The period of the Earth lasting from 5 billion to 2.5 billion years ago. It is the earliest era of the earth's history.

Artificial Insemmination

The process in which male gametes, the spermatozoa, are collected and introduced artificially into the female genital tract for the purpose of fertilization.

Arthropod

Any animal that belongs to the phylum Arthropoda. Arthropods are characterized by an exoskeleton made of chitin and jointed bodies.

Asexual Reproduction

Reproduction, not involving fertilization or genetic recombination, in which a new organism develops from parts of, or from parts produced by, one parent.

Atavism

The sudden reappearance in an animal or a plant of a trait that has existed before only in ancient ancestors.

Australopithecus

The supposed descendants of man with a third the cranial capacity (skull capacity)   that man has.

Autopolyploid

Polyploid that is formed via sexual reproduction.