"Theory: When circumstances cause a population to split into two separate isolated groups, each individual group will evolve in different ways as they adapt to different environmental situations. This process will continue until the two groups are so different that they are no longer capable of interbreeding should they ever come back into contact with each other thus, the origin of species."
The sequence described in the first sentence has been observed in the lab. With regard to the second sentence, has this actually been observed to happen as a testable hypothesis, or is it just inferred based on the fossil record?
Google "ring species." There are multiple observed examples of this.