Prezygotic reproductive barriers prevent fertilisation and the formation of a zygote. They act before the fertilisation of an egg.

Postzygotic reproductive barriers, often produced as a result of hybridisation, reduce the viability or reproductive potential of offspring.

Sympatric speciation is a type of speciation that results within a population without any geographical separation.

Instead, ecological or behavioural separation lead to the groups becoming reproductively separated with no gene flow between them, leading to the formation of separate species.

Sympatric speciation is less frequent than allopatric speciation, and it is more common in plants than in animals.

Geographical isolation prevents gene flow between populations, leading to genetic isolation. Over time, different selection pressures can cause significant differences, leading to the formation of new species.

Allopatric speciation is a type of speciation that results from some members of a population being geographically separated from the rest by a physical barrier like mountains, rivers, or seas.

This leads to reproductive separation, causing the populations to evolve separately and leading to the formation of separate species.

Genetic isolation occurs when two groups of organisms are unable to interbreed successfully, preventing the exchange of genes between the groups.

Reproductive isolation is the inability of two groups of organisms to breed with one another, often leading to the formation of new species.

A species is a group of individuals that are capable of breeding with one another to produce fertile offspring.

New species are formed through speciation, most commonly through reproductive separation followed by genetic change due to natural selection.

Evolution is the change in characteristics of species over time, due to changes in allele frequency.

Evolution can lead to the formation of new species from pre-existing ones as a result of changes to the gene pools of populations over many generations.