One of the more common misconceptions, with a history long before Darwin, is that evolution is progressive; that things get more complex and perfect in some way. In fact, this view is attributed more to social and religious attitudes of 18th and 19th century European culture than to any evidence. It was a given that things are getting better and better, every way, every day. This persisted until long after Darwinism, until the middle of this century (e.g., Teilhard de Chardin). Even Darwin was ambiguous about it, talking on occasion about 'perfection' as a result of selection.
At the time of the 'modern synthesis' [note 9] in the 1940s, the notion of progress was quietly dropped, with a few exceptions like Dobzhansky and Huxley within the synthesis, and Schindewolf and Goldschmidt outside it. Of course, heterodox writers (usually not biologists) like Teilhard and Koestler remained progressionists long after this.
But by the 1970s, progress had been abandoned by working biologists.
Recently, the issue has resurfaced, shorn of the mysticism of earlier debates. Biologist J.T. Bonner argued that there was a rise in complexity of organisms over the long term , and others were arguing for a form of local progress under the terms 'arms race' [Dawkins and Krebs 1979] and 'escalation' [Vermeij 1987]. Gould  felt so strongly about it he was moved to deny that, at least since the Cambrian explosion, there has been any progress at all.
Much of the modern debate centres on what counts as 'progress'. Gould  thinks that the apparent trend to complexity is just a matter of random evolution that started at a minimal 'wall' of complexity:
Others [cf Nitecki 1988] claim that there is only progress because any increase over zero is a net increase, and that different measures will give...