Evolution does not necessarily equate to progress. It's simply about randomly adapting. If we were able to make a properly mechanistic assessment, we'd have an equation to balance out the amount of change necessary in a species, versus the pace at which an environment is changing.
Speckled about some of the Stephen Jay Gould essays I'm reading are some good examples of randomness at work. I've already mentioned snails on Moorea Island, where several isolated niche environments resulted in several (randomly) different populations of snails. Here's a few more illustrations.
Niche environments can change
Essay 3 in Eight Little Piggies (1993) details a species of limpit, Lottia alveus. They fed exclusively on a single species of sea grass, Zostera marina. Moreover, the limpet could only survive in a certain narrow range of salinity. The Atlantic Ocean variety of Lottia was abundant in the 1920s, but was gone by about 1933. Environmental change or disease had killed off most of that sea grass. Some remained, but only outside the limpet's salinity range. So went the special environment niche, and the limpet was gone.
Change doesn't mean improvement
Gould also detailed a species of coral which oscillated between two substantially different sizes several times over the course of its evolutionary history. Undoubtedly responding to environmental pressures, it demonstrates that change isn't a one-way process that forms a steady upward vector of progress. Evolutionary change simply represented serial adaptions to environment.