The Talk.Origins Archive: Exploring the Creation/Evolution Controversy

Darwin's Precursors and Influences

A glossary of historical
terms in evolutionary theory

by John Wilkins

[Last Update: September 5, 2006]

Contents

Allele: A 'value' at a particular position on a genotype of a species. There are usually many values for most positions (locuses or loci) in a species or large population of organisms, which is expressed in the phrase 'most species are polymorphic at most loci'. An allele can cover one base on a gene, or more usually, a sequence of bases on a gene.
Allopatry: The geographical isolation of two or more populations or species. Also, speciation that occurs in geographical isolation from the main population of the parent species. It is thought to be the dominant mode of speciation. A small population of the species is isolated long enough for genetic drift and natural selection to make it different enough in either reproductive behaviour or mechanisms so that if and when it rejoins the original species it is too distinct to interbreed. There is debate in the evolutionary biological discipline as to whether different ecological behaviour and the adaptations needed to survive in them are the result of speciating selection, or follow from selection between the original species and the now reproductively distinct new species which have become that way through drift. Most think that selection is relevant only after allopatric speciation, although recent work has revived the sympatric speciation model.
Archetype: An archetype is the transcendent 'original' that numerous species that have an affinity of design approximate, according to the transcendentalist philosophy that preceded Darwin. The term literally means 'ruling kind'. A term used to describe archetypes is the German Bauplan, meaning 'blueprint' or 'building plan'. Nowadays this German term has lost its essentialist flavour, and instead is understood to represent ancestral novelties shared by all or most of a group of species.
Catastrophism: The name coined by William Whewell in 1832 to describe a view in geology championed by William Buckland that the rate and mechanisms of past geological change are dramatically different than those of today. More recently it has been used to refer to 'episodic' or 'quantum' evolutionary processes, and to scientific models that requires extremely large scale change to account for past developments. It is wrongly applied to the punctuated equilibrium theory of Gould and Eldredge, which involves variable rates but not dramatically distinct causes. See Uniformitarianism.
Evolution/evolutionism: This is in its bare form the thesis that species transform. Some historical varieties involve an assumption of inevitable progress. Others suppose that there is a strong analogy between the development of an organism through its life-cycle and the changes in a species. All sorts of metaphors have been used to describe evolution, including mechanical/physical metaphors of "inertia", and "evolutionary force", organismic metaphors of "racial senescence", "species vitality" and so forth. These have no relation to scientific evolutionary theory, and have been abandoned. Darwinism is a theory of outcomes, and does not insist on progress. Species are seen as lineages that do whatever they do, and are not subject to "racial decay" or "devolution" or "drives to perfection". Initially the term "evolution", which is a Latin term meaning to unscroll or unfold and is used of reading a scroll, was applied to the ontogenetic stage of the life cycle of a form of organism. Since early views of evolution used an analogy with ontogeny, the term was passed over to cover phylogenetic change as well, and then became used exclusively for it.
Genotype: The general structure of a species' or population's genetic makeup. A genotype is comprised of all the various alleles that are available in the gene pool of the species.
Homology: A similarity of structures due to their 'affinity' through an ideal type, or archetype, according to Richard Owen. In modern evolutionary theory, the similarity is homologous if it evolved from the same structure in a common ancestor. Otherwise, any similarity is convergent and therefore 'analogous'. See also transcendentalism.
Macroevolution: A term introduced by Theodosius Dobzhansky in 1937, referring to evolution at levels higher than the populational. Macroevolution in his view was evolutionary change at the level of speciation and above. Recently, the term has been used simply to refer to large scale change, mostly at the superspecies level, eg, by Niles Eldredge.
Macromutation: A term introduced early in the 20th century when the term mutation no longer referred to large scale genetic changes after the integration of Mendelian genetics and Darwinian theory.
Microevolution: A term referring to evolutionary changes beneath the level of the species. It includes, but is not limited to, adaptation to local environments. See also macroevolution.
Mutation: A term introduced in the late-nineteenth century to refer to large scale phenotypic change but which was appropriated by modern genetics to mean any genetic change, large or small. A 'point mutation' is the single substitution of one base. A 'translocation' is the reshuffling of a long sequence. An 'inversion' is the inverting of a long sequence, and so on.
Naturphilosophie: See transcendentalism.
Ontogeny: The development of the organism from the sex cells ('gametes') to birth ('partition' in animals). It includes the 'zygote' and 'fetal' stages.
Parapatry/Peripatry: Existing in neighbouring and nonoverlapping regions. Also, speciation that occurs at the extremes of a species' range, either in environmental terms or geographical location. It is a form of allopatric speciation.
Phenotype: The organism-level traits and characters of a species or individual organism. There are typically economically important, if they function in natural selection, but it is held by some that not all phenotypic traits are selectively biassed. Phenotypic traits are the result of the expression of the genes of the organism. Sometimes a trait is actually a 'norm of reaction', for it may be expressed in different ways in different environments (eg, height depending on diet).
Phylogeny: The 'pedigree' of a species - the branches of the ancestral tree of species from which the current species derives. A related species is derived from a common ancestor. There are two kinds of phylogenies - branching, or divergent, phylogenies, and merging, or reticulate, phylogenies. Hybridisation of two species is a case of reticulation if the result is a viable and reproductively persistent form.
Speciation: The creation of a species through the splitting of one species into two or more, through descent.
Sympatry: Existing in overlapping regions. Also, a contentious but now generally accepted, if rare, mode of speciation where the populations are not isolated, but adopt distinct ecological behaviour and are forced by selection to diverge. One form of sympatry - stasipatry - is the result from genetic (mainly chromosomal) reorganisation. Selection is prominent in sympatric speciation.
Transcendentalism: A philosophy of nature that holds that everything is an approximation to an ideal standard or type. It was popular in the early decades of the nineteenth century, and derives from Platonism and Goethe, the latter tradition known in Germany as Naturphilosophie. On this account, species are ideal types and have no variation that is not degradation of the type. Variation is seen as monstrosity. Some transcendentalists, like Owen, saw species as implementing the types differently, and from this Owen developed his idea of homology (same function from the same part of the archetype) and analogy (same function using different structures).
Uniformitarianism: The name coined by William Whewell in 1832 to describe a view in geology championed by Charles Lyell that the rate and mechanisms of geological change operating in the modern era are sufficient to explain changes in the past. It was contrasted with catastrophism. More recently, uniformitarianism has been applied to any 'steady state' theory or model of historical change, including evolution (cf Gould and Eldredge's Punctuated Equilibrium theory).

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Darwin's Precursors and Influences

A glossary of historical terms in evolutionary theory

A glossary of historical
terms in evolutionary theory