The study of organism divergence, , and adaptation.

See evolution as well as evolutionary ecology and .

From :

The differs in his method and in the problems in which he is interested. His basic question is "Why?" When we say "why" we must always be aware of the of this term. It may mean "how come?," but it may also mean the "what for?" It is obvious that the evolutionist has in mind the historical "how come?" when he asks "why?" Every organism, whether or species, is the product of a long history, a history which in- deed dates back more than 2000 mil- lion years. As has said, "a mature , acquainting himself for the first time with the problems of biology, is puzzled by the circumstance that there are no 'absolute phenomena' in biology. Everything is time-bound and space-bound. The animal or plant or microorganism he is working with is but a link in an of changing forms, none of which has any permanent validity." There is hardly any structure or function in an organism that can be fully understood unless it is studied against this historical background. To find the causes for the existing characteristics, and particularly adaptations, of organisms is the main preoccupation of the evolutionary biologist. He is impressed by the enormous diversity of the organic world. He wants to know the reasons for this diversity as well as the pathway by which it has been achieved. He studies the forces that bring about changes in and (as in part documented by paleontology), and he studies the steps by which have evolved the miraculous adaptations so characteristic of every aspect of the organic world.

We can use the language of to attempt still another characterization of these two fields of biology. The functional biologist deals with all aspects of the decoding of the programmed information contained in the of the fertilized zygote. The evolutionary biologist, on the other hand, is interested in the history of these codes of information and in the laws that control the changes of these codes from generation to generation. In other words, he is interested in the causes of these changes.

It is evident that the functional biologist would be concerned with analysis of the proximate causes, while the evolutionary biologist would be concerned with analysis of the ultimate causes. This is the case with almost any biological phenomenon we might want to study. There is always a proximate set of causes and an ultimate set of causes; both have to be explained and interpreted for a complete understanding of the given phenomenon.

Evolutionary terms and concepts include the following:

Absolute fitnessAdaptabilityAdaptationAdaptive landscapeAdaptive radiationAdaptive zoneAlleleAllele frequencyAllele-neutralAllopatric speciationAnagenesisAnalogyAncestorAncestor speciesAntagonistic pleiotropyAltering gene numberArtificial selectionAssortative matingAverage heterozygosityBalanced mutationBalanced polymorphismBalancing selectionBiased reproductive successBiological species conceptBiogeographyBottleneck (genetic)Breakdown of reproductive barriersCladogenesisClonal expansionClonal interferenceCoefficient of relatednessCommon ancestorConvergent evolutionDifferential successDarwinian evolutionDarwinian fitnessDarwinismDeleterious alleleDerivedDescendant speciesDescent with modificationDetrimental alleleDirectional selectionDisruptive selectionDisruptive frequency-dependent selectionDivergent evolutionDiversifying selectionEcological species conceptEndosymbiotic theoryEvolutionEvolutionary compromiseEvolutionary divergenceEvolutionary ecologyEvolutionExisting variationExtantFitFitnessFixationFounder effectFrequency-dependent selectionGametic isolationGene flowGene poolGenetic bottleneckingGenetic driftGenetic drift: impact of population sizeGenetic drift: impact on allele frequencyGenetic drift: impact on genetic variationGenetic drift: impact on allele fixationGenetic variationGenetic structureGenotype frequencyGeographic variationGeographical barrierGeographical isolationHabitat isolationHard selectionHamilton's ruleHardy-Weinberg assumption # 1Hardy-Weinberg assumption # 2Hardy-Weinberg assumption # 3Hardy-Weinberg assumption # 4Hardy-Weinberg assumption # 5Hardy-Weinberg equilibriumHardy-Weinberg theoremHeterochronyHeterozygous advantageHidden genetic variationHitchhiking (genetic)Homologous structureHomologyHomoplasyHorizontal gene transferHybridHybrid breakdownHybrid vigorHybrid zoneHybridizationIdentical by descentInclusive fitnessIntersexual selectionIntrasexual selectionIntrogressionK selectionKin selectionLineageMacroevolution,  Mate choiceMechanical isolationMicroevolutionMigration (genetic)Modern synthesisMolecular evolutionMolecular homologyMonomorphic (locus)Morphological homologyMorphological species conceptMosaic evolution,  Muller's ratchetMutationNatural selectionNegative selectionNeutral alleleNeutral theoryNeutral variationNew allelesNon-Darwinian evolutionNonrandom matingOrthologous genesPaedomorphosisPanmixisParalogous genesParapatric speciationPeripatric speciationPeripheral isolatesPhyletic gradualismPhylogenetic species conceptPluralistic species conceptPolymorphismPopulation biologyPopulation geneticsPostzygotic barrierPrezygotic barrierPunctuated equilibriumr selectionRandom matingRapid reproductionReinforcementRelativeRelative fitnessReproductive barriersReproductive isolating mechanismReproductive isolationReduced hybrid fertilityReduced hybrid viabilitySecondary endosymbiosisSelectionSelection for reproductive isolationSelective sweepSerial endosymbiosisSexual selectionShared ancestral characterShared characterShared derived characterSpeciationSpecies conceptsSpecies selectionStabilizing frequency-dependent selectionStabilizing selectionSympatric speciationTemporal isolationTradeoffsUltimate causationUniversal treeVertical gene transferVestigial structure