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 unexplored part of the world for empirical inquiry, and baptize a new special science to undertake that inquiry. Rather, new sciences seem most often to grow out of gaps in the understanding of old sciences. Molecular biology is an excellent illustration here; the isolation of DNA in 1869—and the subsequent identification of it as the molecule responsible for the heritability of many phenotypic traits—led to an explosion of new scientific problems: what is the structure of this molecule? How does it replicate itself? How exactly does it facilitate protein synthesis? How can it be damaged? Can that damage be repaired? Molecular biology is, broadly speaking, the science that deals with these questions and the questions that grew out of them—the science that seeks to articulate the patterns in how the chemical bases for living systems behave. This might seem unsatisfactory, but it seems that it is the best answer we're likely to get: molecular biology, like the rest of science, is a work-in-progress, and is constantly refining its methodology and set of questions, both in light of its own successes (and failures) and in light of the progress in other branches of the scientific project. Science is (so to speak) alive.

This is an important point, and I think it is worth emphasizing. Science grows up organically as it attempts to solve certain problems—to fill in certain gaps in our knowledge about how the world changes with time—and is almost never centrally planned or directed. Scientists do the best they can with the tools they have, though they constantly seek to improve those tools. The fact that we cannot give a principled answer to the question "what parts of the world does molecular biology study?" should be no bar to our taking the patterns identified by molecular biology seriously. Just as we could not be sure that R, once identified, would hold in any

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