speciation keywords

Adaptation

Any change in the structure or functioning of an organism that makes it better suited to its environment.

Adaptive radiation

The evolution of a number of different species of plant or animal from one ancestral species; e.g. Darwin's Galapagos finches.

Allele

One of the alternative forms of a gene.

Allele frequency

The occurrence of an allele in a population in relation to other alleles of a gene at the same locus.

Allopatric

Living in areas that are separated by geographic barrier.

Allopatric speciation

Speciation occurring where organisms are initially capable of actually interbreeding but cannot because of a geographic barrier.

Allopolyploid

A polyploid organism, usually a plant, that contains multiple sets of chromosomes derived from different species.

Analogous structures

Structures that are superficially similar but have evolved in different ways; e.g. the wings of birds, bats and insects.

Ancestor

A hypothetical individual possessing the ancestral or primitive characteristics of a group of species.

Autopolyploid

A polyploid organism in which multiple sets of chromosomes are all derived from the same species.

Biogeography

The branch of biology that deals with the geographical distribution of plants and animals.

Bottleneck effect

A reduction in genetic diversity caused by a dramatic reduction in population size - rare alleles may be lost.

Characteristic

A distinctive inherited feature of an organism.

Chromosome

A threadlike structure several to many of which are found in the nucleus of eukaryotic cells.

Clade

A group of organisms that share a common ancestor.

Classification

The arrangement of organisms into a series of groups based on physiological, biochemical, and anatomical or other relationships.

Cline

A gradual variation in the characteristics of a species or population over its geographical range.

Co-evolution

The evolution of unrelated organisms that has taken place together because of a special link between them; e.g. insects and the flowers they pollinate.

Convergent evolution

The development of superficially similar structures in unrelated organisms, usually because the organisms live in the same kind of environment.

Deme

A population; or group of individuals within a species that is largely isolated from other individuals of that species.

Directional selection

Natural selection that favours the establishment of one particular advantageous mutation within a population, resulting in a change in phenotype in that direction.

Disruptive selection

Natural selection that favours the extremes of a phenotype in a population.

Divergent evolution

An accumulation of changes in the gene pools of two (or more) populations, leading to the formation of races, sub-species, species, etc.

Endemic

A species that is restricted to one or a few localities, for example, islands.

Evolution

The gradual process by which the present diversity of plants and animals arose from the earliest and most primitive organisms.

Founder effect

When a new population is established from only a few founders - the gene pool of the resulting population is not representative of the original population.

Gene

A unit of heredity composed of DNA, occupying a specific locus on a chromosome and coding for one polypeptide.

Gene flow

The exchange of genetic information by interbreeding between populations of the same species or between individuals within a population.

Gene pool

All the genes and their different alleles present in a population.

Genetic drift

Evolutionary changes in small populations produced by random variation in allele frequencies and not by natural selection.

Geological record

Fossils preserved in sedimentary rock layers that can be used to trace the evolutionary history of a species.

Germ cell

Any cell in a series of cells that eventually produces gametes.

Gradualism

A theory of evolution which proposes that evolutionary change occurs slowly, resulting in many transitional forms in the fossil record.

Homeotic genes

Genes that have an important role in the control of early development and differentiation in eukaryotic organisms – mutations in these genes can often lead to novel forms.

Homologous structures

Structures that have a similar evolutionary history but have developed to suit different functions; e.g. wings of a bat, flippers of dolphins and arms of humans have all evolved from paired pectoral fins of an ancestral fish.

Hybrid

The offspring of a mating where the parents differ in at least one characteristic. The term is usually applied to offspring of widely different parents; e.g. different varieties/species.

Instant speciation

The formation of a new species through autopolyploidy or allopolyploidy. Because the chromosome numbers of the new 'instant' species do not match that of the original species they cannot interbreed.

Macro-evolution

The formation of a completely new species, genera, etc.

Micro-evolution

The accumulation of (through mutation) of new alleles in a species.

Molecular biology

The study of structure and function of large molecules associated with living organisms, in particular proteins and the nucleic acids DNA and RNA.

Mutation

A permanent random change in the genetic material of a cell that may cause it and all cells derived from it to differ in appearance or behaviour from the normal ('wild') type.

Natural selection

Survival of the fittest. The process of evolutionary change where the organisms with phenotypes best suited to the environment are more likely to survive and reproduce and therefore pass on their successful genes to offspring. 3 types - stabilising, directional and disruptive selection.

Organism

An individual living thing.

Parallel evolution

The development of related organisms along similar evolutionary paths due to strong selection pressures acting on all of them in the same way.

Phenotype

The observable characteristics of an organism.

Phylogeny

The evolutionary history of an organism or a group of related organisms.

Polyploid

Describing a nucleus that contains more than two sets of chromosomes, or a cell or organism containing such nuclei.

Population

A group of organisms of the same species in a defined area.

Primitive feature

A feature that is assumed to have been present in the evolutionary ancestor of a species of group of species. It may or may not have been simpler, depending on the evolutionary history of the species.

Punctuated equilibrium

A theory of evolution that proposes that species usually arise very quickly in geological time, usually as a result of environmental change, and seldom through a process of gradual change.

Reproductive Isolating Mechanism (RIM)

Any feature of an organism that prevents gene flow between members of different species.

Ring species

Two apparently distinct species that are connected by a series of intermediate geographical and structural subspecies between which interbreeding can occur.

Selection pressure

The extent to which organisms possessing a particular characteristic are either eliminated or favoured by environmental demands.

Sexual selection

Selection based on animals choosing a mate based on 'desirable' features or behaviours; e.g. colour, size, nest building ability, etc.

Speciation

The development of one or more species from an existing species. It occurs when sympatric or allopatric populations diverge so much from the parent population that interbreeding cannot occur.

Species

A category used in the classification of organisms that consists of a group of organisms that can usually breed together and produce fertile offspring.

Stabilising selection

Natural selection that acts to maintain the constancy of a species over successive generations by selecting against the extremes of the range of phenotypes for a particular characteristic.

Subspecies

A group of individuals within a species that breed more freely among themselves than with other members of the species and resemble each other in more characteristics.

Sympatric

Living in the same area.

Sympatric speciation

Speciation that occurs where organisms living within the same area are theoretically capable of interbreeding, but cannot because of difference in behaviour, flowering time, etc.

Variation

The difference between individuals of a species.

Vestigial organ

Any part of an organism that has diminished in size during its evolution because the function it serves has decreased in importance; e.g. the appendix in humans.