Thus, cultures can be distinguished by patterns of craftsmanship; for instance, if one excavated sherd of pottery is decorated with a triangular pattern, and another sherd with a chequered pattern, they likely belong to different cultures. Such an approach naturally leads to a view of the past as a collection of different populations, classified by their differences and by their influences on each other. Changes in behaviour could be explained by diffusion whereby new ideas moved, through social and economic ties, from one culture to another.