Definitions of Evolutionary Terms

Adaptation:
The adjustment or changes in behavior, physiology, and structure of an organism to become more suited to an environment. According to Charles Darwin's theory of evolution by natural selection, organisms that possess heritable traits that enable them to better adapt to their environment compared with other members of their species will be more likely to survive, reproduce, and pass more of their genes on to the next generation.

Chromosome:
A double stranded DNA molecule that contains a series of specific genes along its length. In most sexually reproducing organisms, chromosomes occur in pairs, with one member of the pair being inherited from each parent.

DNA:
Deoxyribonucleic acid. A large biological molecule composed of subunits known as nucleotides strung together in long chains. The sequences of these nucleotides contain the information that cells need in order to grow, to divide into daughter cells, and to manufacture new proteins. Changes in DNA result in mutations, which may be beneficial, neutral, or deleterious to the organism. If these changes occur to DNA in sperm or egg cells, they could be passed onto the next generation.

Evolution:
Evolution consists of changes in the heritable traits of a population of organisms as successive generations replace one another. It is populations of organisms that evolve, not individual organisms.

Fact:
In science, a "fact" typically refers to an observation, measurement, or other form of evidence that can be expected to occur the same way under similar circumstances. However, scientists also use the term "fact" to refer to a scientific explanation that has been tested and confirmed so many times that there is no longer a compelling reason to keep testing it or looking for additional examples.

Fossil:
A remnant or trace of an organism of a past geologic age, such as a skeleton or leaf imprint, embedded, and preserved in the Earth's crust, usually in stratified rock.

Hypothesis:
A tentative explanation for an observation, phenomenon, or scientific problem that can be tested by further investigation. Scientific hypotheses must be posed in a form that allows them to be rejected.

Genomics:
A recent branch of genetics that studies organisms in terms of their complete genetic material, including genes and their functions.

Macroevolution:
Large-scale evolution occurring over geologic time that results in the formation of new species and broader taxonomic groups.

Microevolution:
Changes in the traits of a group of organisms within a species that do not result in a new species.

Mimicry:
In biology, mimicry is the superficial resemblance of one species of organism to another species or to a natural object in its surroundings. Some kinds of mimicry result in a selective advantage for concealment and protection from predators. Another type of mimicry enables protection to the mimic through its resemblance to another species that is toxic or in some other way dangerous.

Mutation:
A change in the sequence of one or more nucleotides in DNA. Such changes can alter the structure of proteins or the regulation of protein production. In some cases mutations result in the organism possessing these altered traits to have a greater or lesser chance of surviving and reproducing in a given environment than other members of its species.

Natural selection:
Differential survival and reproduction of organisms as a consequence of the characteristics of the environment.

Paleontologist:
A scientist who studies fossils to learn about ancient organisms.

Protein:
A large molecule consisting of a chain of smaller molecules called amino acids. The sequence of amino acids and the molecule's three-dimensional structure are coded by the instructions in DNA and determine a protein's specific function in cells or organisms.

Population:
A group of organisms of the same species that are in close enough proximity to allow them to interbreed.

RNA:
Ribonucleic acid. A molecule related to DNA that consists of nucleotide subunits strung together in chains. RNA serves a number of cellular functions, including providing a template for the synthesis of proteins and catalyzing certain biochemical reactions. The structure of RNA is determined by the sequence of nucleotides on DNA.

Science:
The use of evidence to construct testable explanations and predictions of natural phenomena, as well as the knowledge generated through this process.

Sedimentary:
Rocks formed of particles deposited by water, wind, or ice.

Selective breeding:
The intentional breeding of organisms with desirable traits in an attempt to produce offspring with enhanced characteristics or traits that humans consider desirable. This process is also known as "artifical selection" (compare with "natural selection").

Speciation:
The evolutionary processes through which new species arise from existing species.

Species:
In sexually reproducing organisms, species consist of individuals that can interbreed with each other.

Survival of the fittest:
A term that refers to the survival of only those organisms best able (fittest) to obtain and utilize resources, resulting in the evolution of organisms that are best adapted to the environment. Darwin used metaphorically to describe "natural selection." The phrase was invented by the 19th century philosopher Herbert Spencer It has been misapplied through history to explain and justify social and economic inequities in human populations ("social Darwinism") or as a method for improving the human condition through selective breeding (eugenics). Survival alone is insufficient for evolution - it's reproduction - passing on of genes that really counts. Most modern biologists no longer use this term when describing or discussing natural selection.

Theory:
A plausible or scientifically acceptable, well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena and predict the characteristics of as yet unobserved phenomena.

Trait:
A physical or behavioral characteristic of an organism.

From Science, Evolution, and Creationism, National Academy of Sciences and Institute of Medicine. © 2008 National Academy of Sciences