After having seen the massive feedforward and feedback forces that resist change, it is almost surprising that there is any change at all, but there is.

We must understand what enables change to come through, and for that we have to understand which are the selection criteria that halt some changes and let some others pass. We must also understand the forces behind the generation of potential changes.

The mechanisms of evolution that are described in Chapter 7 are complicated, so I thought it would be easier to start with examples to illustrate the societal mechanisms of generation and selection of changes.

In this section we study two cases, scientific progress and product innovation, to extract from this empirical material some principles used by society to select what makes changes acceptable, in the symbolic and material realms.