Der Fluss des Lebens

Glossary

Acceleration  -  A category of heterochrony (peramorphosis) in which descendant shows a faster rate of development events

Acclimatization  -  Physiological adaptation to natural changes in the environment, e.g. temperature, altitude

Adaptive radiation  -  An episode of rapid and sustained increase in the numbers of species in a higher taxon, linked with marked adaptive diverstification

Adaptive zones  -  Clusters or constellations of adeptive peaks in an adaptive landscape, separated from each other by major adaptive troughs, yielding natural ecological groupings of species

Allele  -  One of the different versions of a gene that cam occur at the locus occupied by that gene. Often there are just two versions, one frequently dominant over the other. Sometimes however, they are several versions, only two of which can be present in any given diploid organism

Allometry  -  The differential relative growth of two age-dependent variates

Allopatric speciation  -  Speciation that occurs as a result of two or more populations diverging while allopatric, or allopatric for at least part of the speciation process

Anagenesis  -  Descent with modification within a single evolutionary lineage

Analogous  -  Similarities between organisms which are due to convergent evolution are said to be analogous

Archaean  -  The geological era spanning the period from 3800Ma to 2500Ma ago. Often referred to as the Age of Prokaryotes

Glossary

Arms race  -  A pattern of evolution involving two interacting organisms in which adaptation in one organism leads to counter-adaptation in the other, e.g. predator and prey

Artificial selection  -  Selective breeding of organisms by humans

Asexual reproductive  -  Reproduction that does not involve meiosis or the production or fusion of gametes

Atavism  -  The reappearance in an individual of certain characters, typical of remotre ancestors, that have been absent in more recent generations

Autapomorphy  -  A derived character state unique to one taxon

Autochthonous  -  Describes a fossilized organism preserved in life position

Biogeographical regions  -  Major subdivisions of the Earth's land surface characterised by distinctive suites of plants and animals

Biogeography  -  The study of geographical distribution of animals and plants

Body fossils  -  The original or altered remains of organisms which have been preserved, usually by burial in sediment or more rarely by other means

Centres of origin  -  Areas where the ancestors of particular plant or animal taxa evolved and from where they subsequently spread out to colonise other regions, according to dispersal biogeography hypotheses

Chronospecies  -  Arbitrary divisions of a single evolutionary lineage, defined on the basis of morphological change

Glossary

Clade  -  A single whole branch of a phylogeny; i.e. a grouping of all the descendants of any given species

Cladisitic biogeography  -  The application of cladistic analysis to geographical distribution data for taxa as well as to phylogenetic characters

Cladistics  -  A systematic method whereby taxa are heirarchically clustered according to inferred relative recency of common ancestry, based upon their shared derived character states

Cladogenesis  -  The division of evolutionary lineages by speciation, causing a proliferation of species

Cladogram  -  A diagram depicting the cladistic relationships of any three or more taxa, ehich are placed at the terminations of a tree comprising successive dichotomous branches with each branching node recognised from one or more shared derived character states

Cline  -  A continuous gradation in some measurable character, whether morphological, physiological, genetic, chromosomal or behavioural, across the range of a species, or any hybrid zone between species or sub-specific types where there is such continuous gradation from one type to another

Coevolution  -  The evolution of reciprocal adaptations of two or more species that have prolonged, close interactions

Competition  -  An interaction between individuals, brought about by a shared requirement for a resource in limited supply, and leading to a reduction in the survivorship, growth and/or reproduction of the competing individuals concerned

Glossary

Competitive exclusion  -  Prevention of one species from maintaining a viable population as a result of competition with another species

Convergent evolution  -  Evolution of two or more lineages towards similar morphology or adaptations so that differneces between the lineages decrease

Divergent evolution  -  Evolution that results in increasing morphological difference between initially more similar lineages

Endemic species  -  Species confined to one particular country or region

Evolutionary equilibrium  -  A population is said to be evolutionary equilibrium with respect to a given gene at the point where there is no effect of natural selection on that gene

Evolutionary fauna  -  A set of higher taxa (especially classes) that have similar histories of diversification and that together dominate the biota for a long interval of geological time. The three Phanerozoic evolutionary faunas are the Cambrian, the Palaeozoic, and the Modern

Evolutionary novelties  -  Structures, biochemical properties or habits that appear to evolve without obvious precedent

Evolutionary systematics  -  A systematic method whereby taxa are hierarchically clustere according to all available forms of evidence for evolutionary relationships; the standard approach until the appearance of phenetics and cladistics in the 1950s and 1960s

Glossary

Evolutionary trend  -  A term used loosely for any sustained tendency for evolutionary change in a particular direction. Anagenetic trends occur within single lineages, whilst whole-clade trends, which may be uncoupled from anagenetic trends, concern a net shift in some variate when all the constituent lineages in a clade are taken into account

Extinction  -  The loss of species or higher taxa. A taxon becomes extinct when all the populations of that taxon have died out (global extinction). The term may also apply to a single population (local extinction)

Fecundity  -  The number of eggs or offspring produced by an organism

Fossil-Lagerstatten  -  German term (sing. fossil-Langerstatte) meaning 'fossil bonanza', introduced by the German palaeontologist Adolf Seilacher to describe sedimentary deposits that are an especially rich source of fossil material

Founder effect  -  The effect on genetic variability of the small size of a colonising, or 'founder', population (which may consist of only one or a few individuals). Such a population can never contain more than a fraction of the total genetic variability of the parent population

Fundamental niche  -  The niche which can be occupied by a species in the absence of competitors, predators and other species that adversely affect it

Gene flow  -  The spread of alleles from one breeding population to others, by the dispersal of gametes or zygotes or by the emigration of adults

Gene pool  -  The total set of genes present in a population

Gene transfer  -  The injection of DNA from the same or another species into a zygote or early embryo

Glossary

Genetic bottleneck  -  Loss of genetic variability in a population following a reduction in population size

Genetic drift  -  Random changes in the frequencies of alleles within a population

Genetic revolution  -  A major reorganisation of the genome to a new coadapted combination of alleles; effectively a shift from one adaptive peak to another

Genome  -  The totality of all the genes (or nuclear DNA) of a cell

Guild  -  A group of species that exploit a particular environmental resource in a similar way, e.g. seed-eating or insect-eating birds

Heterochrony  -  A (genetically determined) change in the timing or rate of developmental events, relative to the same events in the ancestor. The two major categories are paedomorphosis and peramorphosis

K-strategist  -  An organism, the life history of which is adapted to maximise its competitiveness and adult survival

Karyotype  -  The number and constitution of the chromosomes in each cell of an individual eukaryote

Key evolutionary innovation (KEI)  -  A novel feature in anorganism that is hypothesised to have been preadaptive for new ecological opportunities (by introducing some major fitness benefit)

Kin selection  -  A form of natural selection operating indirectly on an allele by favouring the relatives of the individual having the allele, as these are likely also to be carrying the allele concerned by descent from a common ancestor

Glossary

Macroevolution  -  Evolution above the species level; this is, the patterns of change in the forms of organisms and in their diversity arising from the appearance and disappearance of species, and the processes involved in such changes

Mass extinction  -  An episode of large-scale extinction affecting many different groups of organisms within a short interval of geological time

Mass mortality  -  The death of large numbers of individual organisms in a single event

Mechanical isolation  -  Reproductive isolation between two species or sub-specific types due to differences in the mechanical structure of the reproductive organs or genitalia which impede or prevent the transfer of gametes between them

Mimicry  -  The resemblance of one organism (the mimic) to another organism (the model), such that the two organisms are confused by a third organism

Monophyletic  -  A taxon which comprises an entire single clade of organisms

Monozygotic  -  Twins (or triplets, quadruplets, etc) that develop from atypical division of one zygote

Mosaic evolution  -  Evolution within a lineage such that different features change at different times or different rates

Mutation  -  Any heritable change brought about by an alteration in the genetic material of an organism. In its narrowest sense it is the alteration, delation or insertion of a single base (or sequence of bases) in a DNA molecule

Neo-Darwinism  -  The version of Darwin's theory of evolution by natural selection refined and developed in the light of modern biological knowledge (especially genetics) in the mid-20th century

Glossary

Niche  -  The n-dimensional hypervolume within which a species can maintain a viable population, the dimensions being all those environmental factors that affect survival and reproduction

Orthogenesis  -  The now discreditesd idea that certain evolutionary trends reflect an intrinsic tendency within organisms to evolve in certain directions that selection cannot regulate, reducing the functional adequacy of individuals, and eventually leading to the lineage's extinction

Paedomorphosis  -  A category of heterochrony in which the descendant shows underdevelopment relative to the ancestor.

Palaeontology  -  The study of life in the past as recorded by fossil remains

Paraphyletic  -  A taxon which comprises only a part of a single clade, from which one or more subordinate clades have been removed because they are deemed to represent distinct grades of organisation

Phylogeny  -  An evolutionary tree showing the inferred relationships of descent and common ancestry of any given taxa

Polyphyletic  -  A taxon which assembles species with independently evolved similarities (derived, therefore,from separate ancestors). Such taxa are rejected from modern systems of classification

Polyploidy  -  The possession of more than two sets of the haploid number of chromosomes (n). The 'normal' diploid has 2n chromosomes, while a polyploid has 3n or more  

Glossary

Preadaptation  -  The phenomenon whereby some structures or processes in ancestors, whether already selected for a certain function or present as selectively neutral features, are fortuitously suited for transformation to a new adaptation in descendants. Such structures or processes are seen in retrospect to have been suited to perform a radically new function with relatively little change of form

Prokaryote  -  A unicellular organism in which the hereditary material is not separated from the cytoplasm by a nuclear membrane, nor is it differentiated into chromosomes, and there are no membrane-bound organelles

Punctuated equilibrium  -  A model in which species are expected to arise by rapid (punctuational) evolution of small, isolated populations, but theresfter to show negligible morphological change (stasis)

Secondary sexual characters  -  Characters in which the two sexes of a species differ, excluding the gonads, their ducts and associated glands

Sexual dimorphism  -  The existence, within a species, of differences in morphology between sexes

Speciation  -  The multiplication of species, i.e. the division of one species during evolution into two or more separate species

Symbiosis  -  The living together in permanent or prolonged association of members (symbionts) of two different species with beneficial or deleterious consequenes for at least one of the parties

Synapomorphy  - A derived character state shared by two or more taxa and held to reflect their common ancestry

Glossary

Systematics  -  The study of the diversity amongst animals and plants, their classification, and the relationships amongst them

Taxonomic diversity  -  The number of constituent taxa (e.g. species, genera, families, etc.) in a higher taxon at any given time in geological history

Text: Skelton, P. 1993. Evolution: A biological and palaeontological approach, The Open University, pp1031-1046