The types of reduction in genetics that have so far been considered in this book have been (a) and (c), that is, weak reduction and abstract hierarchical reduction, respectively. The former, considered in Chapter 4, assumed no structure at all for the genotype. The latter, considered in Chapter 5, assumed the genotype to be hierarchically organized, but did not assume that this hierarchy (of linkage groups, loci, and alleles) is one in physical space. This chapter will turn to strong reduction [type (e), also called “physical reduction,” see below], which is the type most conventionally associated with the so-called molecular revolution in biology. This type of reduction assumes a spatial basis for a hierarchical reduction, that is, quite literally, the behavior of wholes is supposed to be explained by those of their constituent parts. In this chapter, unless explicitly indicated otherwise, “reduction” will only be used here in the sense of “strong reduction.”

In genetics, given that the physical objects associated with genes are microscopic parts of cells, strong reduction is almost necessarily a reduction to an F-realm that, to some level of approximation, must be one in which the basic interactions are physical or chemical. It is tempting, therefore, to take the theory that is supposed to describe all interactions of matter at this level of organization, quantum mechanics, and its domain as the F-realm for these reductions.