Early biologists saw development and progression in nature long before the theory of evolution. The concept of a progression of life from lower to higher, from less perfect to more perfect was fundamental both in primitive theology and early scientific thought.
But examination of the actual record of life and of the evolutionary processes raises such serious doubts regarding this over simple concept that we must reject it altogether. Yet, there are many changes in the history of life. Deeply ingrained in our thinking, especially on political and social subjectsthat change is progress.
But progress is not merely movement but movement in a direction from worse to better, lower to higher, or imperfect to more nearly perfect. Biology provides examples not only of this kind of movement but also of retrogression or degeneration. There is no criterion of progress by which it can be considered a universal phenomenon of evolution. Progress is not a basic property of life common to all its manifestations.
However, there seems to be only one progressive change that involves life as a whole, a tendency for life to expand, to fill in all the available spaces in the livable environment. This is one possible sort of progress.
There are other progressions that could be considered a kind of progress. The increasing ability of humans to exercise control over their environment is one. Biological progress might also be seen in the complication of structure as in the development of multi-celled organisms.
But, it must be emphasized evolution is not invariably accompanied by progress. Progress has occurred within it but is not of its essence. Aside from the broad tendency for the expansion of life, which is also inconstant, there is no sense in which it can be said that evolution is progress.