Speciation – AP Biology College Board Revision

Understanding Speciation

Speciation is the process through which new, distinct species evolve from existing species over time.
This evolutionary process often occurs when a group within a species becomes genetically isolated from the rest of the species.
The genetic isolation can result from a variety of causes, including geographical barriers (such as mountains or bodies of water), reduced gene flow due to different mating preferences, or changes in the genetic makeup of a group.
Over time, the isolated group accumulates so many genetic differences that it can no longer interbreed with the non-isolated original group to produce viable offspring.

Speciation generally begins with a populational split; a group of individuals of the same species becomes separated from the rest of the species.
Multiple factors can cause a population split, including migration, geographic isolation, or evolution of different mating rituals.
The separated group undergoes different evolutionary pressures from the original group, leading to different selection forces on their gene pool.
Over time, these different selection forces result in different adaptations in each group, causing the two groups to become distinct species.

Speciation primarily occurs in two ways: allopatric speciation and sympatric speciation.
Allopatric speciation is when geographical isolation separates one population from the rest of the species, preventing gene flow and leading to the evolution of a new species.
Sympatric speciation, on the other hand, is when a new species evolves while sharing the same geographical area as the original species. This typically happens due to potent selective forces, such as behavioural isolation or polyploidy in plants.

Speciation is a fundamental driver of biological diversity. Each speciation event increases the total number of species on Earth.
It’s also how evolutionary branching occurs, where one species diverges into two or more different species.
Through a long history of multiple speciation events, life’s immense diversity has accumulated, from simple single-celled organisms to the myriad forms of complex multicellular life today.