Drawing general conclusions from conceptual practice in genetics
Scientific metaphysicians might respond to my skepticism about the idea that the intermediate-scale world that biologists engage lacks an overall structure by retreating from biology. “Perhaps biology is not ready for metaphysics. Perhaps geneticists haven’t found nature’s joints. But the joints must exist. If not in DNA, then elsewhere.” I disagree. Genetics is sufficiently advanced to draw important metaphysical conclusions. But to draw them we must broaden our attention from a narrow focus on its theories and theoretical concepts, to how its theories and concepts are used in the context of broader investigative and manipulative practices. In addition, we should not assume at the outset that the world must have an overall structure, or that living systems and processes must have an overall structure at the scale being manipulated and investigated by biologists.
The practice of genetics enables biologists to control and manipulate a wide variety of phenomena and to gain new knowledge about the entities and processes of life. If the metaphysical ideas set out in section 4 were true, then the practice of contemporary genetics would presumably take a different form than it does. It would be based on a gene concept that provided a canonical parsing of DNA. But contemporary gene concepts do not provide such a parsing (or imply that such a parsing exists even in principle). Instead, biologists rely on gene concepts that enable them to parse DNA in a multiplicity of ways. Why does their practice take this form? The simple answer is “because it works.” Practice has been adapted to work in the reality of the world that biologists are engaging.
A metaphor might be helpful here.13 Biologists using genetics to investigate the workings of organisms are like newcomers trying to navigate in a strange city. Suppose they enter the city of Arles in southern France. The streets of Arles lack a general, overall structure. You can learn to navigate in one small part of the city, but that does not help you anticipate the layout of another part of the city. Contrast 
this with newcomers arriving in the western Canadian city of Calgary. The streets of Calgary are laid out in a grid with four quadrants. “Streets” are oriented north/south (they run from north to south or from south to north), and “avenues” are oriented east/west. Streets are numbered sequentially in each quadrant, starting from the center of the city. For example, streets in the northwest quadrant are named 1 Street NE, 2 Street NE, and 3 Street NE. Avenues are named in the same fashion, for example 1 Avenue NE 2, Avenue NE, and 3 Avenue NE.
The best strategy for learning to navigate in cities like Calgary is to key into the overall structure. Exceptions to the grid structure exist near rivers and railroad tracks, but knowing there is some general, overall structure will facilitate newcomers’ exploration of the city. Newcomers investigating Washington, DC would also be well-served by a strategy that rests on the assumption that there is some overall structure of streets, even though the structure of streets in DC is quite different than the structure of streets in Calgary. But newcomers to Arles should strategize their investigation differently because there is no overall structure to the street layout in Arles. My claim is that the domains being investigated by biologists using genetics are more like Arles than Calgary. We can infer this from the nature of the practices used in genetics. The world within organisms, like the street layout of Arles, is a mess. The practice of genetics has been adapted to navigate through the mess; the molecular concept of the gene is designed to enable biologists to investigate and control causal pathways within a messy, dynamic entanglement of interacting causal chains, an entanglement that they do not understand in its complexity.
The idea that the reality within organisms lacks an overall structure can be generalized. It implies that the world in its entirety lacks a general overall structure. That is, it suggest that the world lacks a “the structure” that spans scales. But perhaps the domain (part and scale of the world) investigated by genetics is an exception. Perhaps the world is like the street layout of Calgary, and the living portion of the world at the scale being investigated by geneticists is akin to the portion of Calgary located near the Elbow River, where the grid breaks down and the street layout is messy.
In section 2, I described the generality across scales thesis, which states that features of the world at intermediate scales (such as the scales of macromolecules, cells, organisms, and ecosystems) are not necessarily less general than features at the smallest and largest scales. The generality across scales thesis implies that the feature of having no overall structure could obtain quite generally across scales being investigated by biological and social scientists, and by physical scientists in many fields as well. Why should we think that the universe has structure at every scale or that the principles (or laws) at the smallest scales provides an overall structure at larger scales ?15 Is the structure of the world a fractal?
There is much work to be done to clarify the widespread assumption that the world has a “the structure” and to articulate the contrary no general structure thesis. This work will require drawing upon traditional work in metaphysics as well as carefully analyzing a greater breadth of scientific practices across a range of sciences, biological, social, and physical. This chapter offers a start by arguing for the idea that the reality engaged by geneticists lacks an overall structure and by raising the question of whether the widespread metaphysical assumption that the world has a “the structure” is mistaken.
-  thank John Norton for suggesting this metaphor.
-  The distinction and metaphor presented here is somewhat similar to Feynman’s distinction between Greek andBabylonian approaches to theorizing (1967) as discussed by Wimsatt (2007). But Wimsatt’s rich and provocative discussion seems to assume that the world itself has a fundamental structure even though physical theoriesdo not.