science has diverged into two? Perhaps the most important choice characterizing a particular science's domain is the choice of what measurements to make, and on what parts of the world. That is: the choice of a domain is largely constituted by the choice to treat certain parts of the world as individuals, and the choice of what measurements to make on those individuals. Something that is treated as an individual by one special science might well be treated as a composite system by another; the distinction between how human brains are treated by cognitive psychology (i.e. as the primary objects of prediction) and how they're treated by neurobiology (i.e. as aggregates of individual neural cells) provides an excellent illustration of this point. From the perspective of cognitive psychology, the brain is an unanalyzed individual object—cognitive psychologists are primarily concerned with making measurements that let them discern patterns that become salient when particular chunks of the physical world (that is: brain-containing chunks) are taken to be individual objects. From the perspective of neurobiology, on the other hand, brains are emphatically not unanalyzed objects, but are rather composites of neural cells—neurobiologists make measurements that are designed to discern patterns in how chunks of the physical world consisting of neural cells (or clusters of neural cells) evolve over time. From yet another perspective—that of, say, population genetics—neither of these systems might be taken to be an individual; while a population geneticist might well be interested in brain-containing systems, she will take something like alleles to be her primary objects, and will discern patterns in the evolution of systems from that perspective.
We should resist the temptation to become embroiled in an argument about which (if any) of
- We'll explore this point in much more depth in Chapter Two.