I think colors are a good analogy. Colors exist and are distinct at certain distances from each other, but things start to get blurry the closer two colors are

I think colors are a good analogy. Colors exist and are distinct at certain distances from each other, but things start to get blurry the closer two colors are to each other. For instance, is turquoise blue? Is it green? It's kinda both. Same with organisms and populations. The farther away (evolutionarily speaking) two populations of interbreeding organisms are, the easier it is to distinguish them into different species. The closer they are, the more things start to look like turquoise.