I don't think you understand evolution exactly. Evolution doesn't just take place in one generation. It's multiple generations of change that turn one species into a different species. Then, through competitive exclusion, that new species may drive out the old species to extinction. But, adaptations only prevail in a species if they are helpful in surviving, hence why humans aren't evolving still, and most likely won't until space travel. Most of the times a species divulges is when a natural desperation occurs, I.E some animals are trapped in an island from a flash flood while others are on a different island. Those two different environments would have different predators, different plant life therefore different coloring, and different prey. So, while one species would stay the same on the island that didn't change, the other island would create a new species. Therefore the old species still lives, because it is suited for its environment. Edit: Also can you give me a link to that article or video that's from, because I have a feeling your taking that out of context simply because of how ill-stated that is