# Speciation

The formation of a new species when two populations become so different they can no longer breed together.

Biology (school) · Part 06: Variation and evolution · Card 6 of 11 · Last updated 2026-10-19

## Analogy

Two dialects growing so far apart that they become separate languages.

## In practice

Populations separated by an island may evolve into different species.

## Practice

### Flashcards

- **What can cause a new species to form?** Populations are isolated and change until they can no longer interbreed.

## Questions people ask

### What is a species?

A species is a group of organisms that can breed together to produce fertile offspring. A horse and a donkey can mate, but their offspring, the mule, is usually infertile, so they are separate species. This definition does not fit every organism, such as those that reproduce without mating.

### How does isolation lead to new species?

If a population is split by a mountain, sea or river, the two groups live in different conditions and face different selection pressures. Different mutations also appear. Over many generations they may become so different that they can no longer breed together, forming two species.

## Related concepts

- [Natural selection](https://studyvisually.com/learn/science/biology-school/biology-school-part-6/biology-school-part-6-concept-3)
- [Adaptation](https://studyvisually.com/learn/science/biology-school/biology-school-part-6/biology-school-part-6-concept-4)
- [Evolution](https://studyvisually.com/learn/science/biology-school/biology-school-part-6/biology-school-part-6-concept-5)
- [Extinction](https://studyvisually.com/learn/science/biology-school/biology-school-part-6/biology-school-part-6-concept-8)

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