Allopatric and sympatric speciation | Biology | Khan Academy

A species is defined as a group of organisms that can interbreed and produce fertile offspring.
Examples include Asian elephants and African elephants, which are separate species that cannot interbreed to produce fertile offspring.
The separation of species plays a crucial role in discussions about evolution.

Speciation: The formation of new species, answering how divergence occurs within populations to the extent that they can no longer interbreed.

Evolutionary trees illustrate the branching of species from a common ancestor, as seen in the lineage of elephants:
- Common ancestor to Asian and African elephants shared with extinct species like the mammoth and Anancus.
Speciation occurs when new species emerge from ancestral ones over time.

Allopatric Speciation: Formation of new species due to geographic separation.
- Etymology: "allo" means other and "patric" refers to homeland.
- Example: Antelope squirrels:
  - Originally one species living on both sides of a now-Grand Canyon.
  - Geographic isolation due to the canyon led to genetic drift and natural selection, resulting in Harris' and white-tailed antelope squirrels.

Sympatric Speciation: Formation of new species while remaining in the same geographical area.
- Example: Rhagoletis pomonella (fruit flies):
  - Originally laid eggs in hawthorn fruit until the introduction of apples by European settlers.
  - Subgroup began using apples for reproduction, leading to behavioral isolation despite being in the same area.
  - If divergence persists, it may lead to a lack of interbreeding in the future.
Another example involves polyploidy in plants:
- Diploid plants typically have two sets of chromosomes.
- Errors in meiosis can produce tetraploid plants with four sets of chromosomes.
- Tetraploid plants may only reproduce with similarly polyploid plants, forming a new species different from the diploid.

Changes in breeding cycles and preferences can lead to speciation.
- Example: Different preferences for host fruits in Rhagoletis pomonella.
In plants, errors in meiosis leading to polyploidy can promote diversity and new species formation.

The understanding of species and their evolution is crucial for biological discussions.
Insights into allopatric and sympatric speciation expand the comprehension of biodiversity and species formation.