I'd say that the process of evolution is universal , because descent with modification, apparently happens amidst all living things. But evolution isn't teleological, in that all life inherently is progressing in a particular direction.
So to your implied question of what makes some species chosen ones, so to speak, and others left behind, especially when you've got similar organisms in the same environment: How does this sound to you?
Like already mentioned, mutations are random. Different ones happen in different species as well as among individuals within a species. Also, there can me many niches within the same local environment.
But since you don't see fishes generally needing digits or limbs like tetrapods to keep passing on their genes, there's no real pressure to take on those changes. A certain mutation may only be advantageous in a particular niche within an environment, and only individuals with the suitable mutations could exploit it. This could bring about a different subpopulation.