Two general concepts in evolutionary biology have fundamental application to our understanding of the evolution of oviposition behavior in tephritid flies, namely, the concepts of opportunism and key innovation. The first,


, refers to the opportunistic nature of natural selection. Natural selection does not necessarily move organisms along the path that leads to the peak of highest fitness on the adaptive landscape. Rather, natural selection often chooses a relatively expedient path, even if that path does not lead to a theoretically maximum fitness. There are two types of opportunism that we will address in this chapter. The first involves opportunistic use of what the animal itself has available to be modified to serve a particular function. The conversion of the second pair of wings in the Diptera to the halteres, structures that serve a gyroscopic function, is a classic example of morphological opportunism in natural selection.