Speciation
Speciation is the evolutionary process by which populations evolve to become distinct species, typically through the accumulation of reproductive barriers that prevent gene flow between diverging lineages. It is the source of biodiversity and occurs through several modes, most commonly allopatric speciation (geographic isolation) and sympatric speciation (divergence without geographic barrier). The biological species concept defines a species as a group of organisms that can interbreed and produce fertile offspring, making reproductive isolation the key criterion.
Modes of Speciation Compared
| Mode | Geographic Isolation? | Mechanism | Example | Speed |
|---|---|---|---|---|
| Allopatric | Yes — physical barrier | Geographic separation prevents gene flow | Galapagos finches | Slow (thousands of generations) |
| Sympatric | No — same location | Ecological or behavioural isolation | Apple maggot fly host shift | Variable |
| Parapatric | Partial — adjacent ranges | Selection stronger than gene flow | Grass on mine tailings | Moderate |
| Peripatric | Yes — small isolated population | Founder effect + drift + selection | Island colonisations | Can be rapid |
| Polyploidy | No — genomic duplication | Chromosome doubling creates barrier | Hexaploid wheat | Can be single generation |
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Related Terms
Evolution (biology)
Biological evolution is the change in heritable characteristics of biological populations over successive generations, driven by mechanisms such as natural selection, genetic drift, gene flow, and mutation. It unifies all of biology by explaining the diversity of life on Earth through descent with modification from common ancestors. Evolution operates at multiple levels, from changes in allele frequencies within populations (microevolution) to the origin of new species and higher taxa (macroevolution).
Gene Flow
Gene flow, also called gene migration, is the transfer of alleles or genes from one population to another through the movement and interbreeding of individuals. It tends to homogenise allele frequencies between populations, reducing genetic differentiation, and can introduce new alleles into a population or change the frequencies of existing ones. Gene flow counteracts the genetic divergence produced by natural selection, drift, and mutation, and is a critical factor in whether populations will diverge enough to speciate.
Founder Effect
The founder effect is the loss of genetic variation that occurs when a new population is established by a small number of individuals (founders) from a larger source population. Because the founders carry only a random, limited sample of the original alleles, the new population will differ genetically from the source population and will have lower genetic diversity. The founder effect is a special case of genetic drift and is often responsible for the high prevalence of certain genetic conditions in isolated human populations.
From Latin "species" (kind, appearance, sort) + Latin "facio" (to make). The term was introduced in the 20th century; Ernst Mayr's 1942 book "Systematics and the Origin of Species" formalised the biological species concept and the study of speciation mechanisms.