Isolation and variation are the factors involved in the formation of new species. Isolation refers to the separation of populations, while variation refers to the genetic differences that arise within populations. Both of these factors play a crucial role in driving the formation of new species.

Isolation:
- Isolation can occur in several ways, such as geographical barriers (e.g., mountains, rivers, oceans) or reproductive barriers (e.g., differences in mating behaviors, reproductive anatomy).
- When populations become isolated from one another, they are no longer able to freely exchange genetic material through gene flow.
- Without gene flow, populations can evolve independently and accumulate genetic differences over time.
- These genetic differences can eventually become significant enough that individuals from different populations are unable to produce viable offspring, leading to the formation of new species.

Variation:
- Variation refers to the genetic differences that exist within a population.
- This genetic diversity arises due to mutations, which are random changes in the DNA sequence.
- Mutations can introduce new genetic variations into a population, which can then be acted upon by natural selection.
- Natural selection favors individuals with traits that are advantageous in their specific environment, allowing them to survive and reproduce at higher rates.
- Over time, these advantageous traits become more common in the population, while less advantageous or detrimental traits are eliminated.
- This process, known as adaptive evolution, can lead to the formation of new species as populations diverge genetically and phenotypically.

The combination of isolation and variation is essential for speciation to occur:
- Isolation prevents gene flow between populations, allowing them to evolve independently.
- Variation provides the raw material for natural selection to act upon, driving adaptive evolution.
- As populations become more genetically and phenotypically distinct due to isolation and variation, they can eventually reach a point where they are reproductively isolated and can no longer interbreed.
- At this stage, they are considered separate species.

In summary, isolation and variation are two key factors involved in the formation of new species. Isolation prevents gene flow between populations, while variation provides the genetic diversity necessary for adaptive evolution. Together, these factors contribute to the divergence and eventual reproductive isolation of populations, leading to the formation of new species.