Organic Progress and Evolutionary Theory

Progress is defined as change towards the better. This definition, comprising both a descriptive and a normative element, can be applied in the organic domain to the history of living organisms. If evolutionary biologists struggle to live with organic progress, they also seem unable to live without it. Are there any theoretical arguments for using the normative terms 'good' and 'better' within evolutionary theory? How do we clarify the idea that some 'change towards the better' is conceptua...