There is no real 'progress' in the idea of evolution. Evolution is simply the generation of diversity and shaping diversity by environmental selection. There are multiple branches possible at each and every stage during evolution. The only trend in evolution seems to be that more complex body designs have emerged over time. However It is not as if the older designs are inefficient. In fact both older and simpler design also still survive. Bacteria, one of the simplest life forms inhabit in the most adverse environment like hot springs, deep sea, thermal vents and the ice in Antarctica.
Thus, evolution should not be equated as 'ladder of progress' rather occurs as branches of trees. Even human beings are not the pinnacle of evolution, but simply yet another species in the teeming spectrum of evolving life.