3438 | J. Howard Molecular Biology of the Cell Quantitative cell biology: the essential role of theory

ABSTRACT Quantitative biology is a hot area, as evidenced by the recent establishment of institutes, graduate programs, and conferences with that name. But what is quantitative biol-ogy? What should it be? And how can it contribute to solving the big questions in biology? The past decade has seen very rapid development of quantitative experimental techniques, especially at the single-molecule and single-cell levels. In this essay, I argue that quantitative biology is much more than just the quantitation of these experimental results. Instead, it should be the application of the scientific method by which measurement is directed toward testing theories. In this view, quantitative biology is the recognition that theory and models play critical roles in biology, as they do in physics and engineering. By tying together experi-ment and theory, quantitative biology promises a deeper understanding of underlying mech-anisms, when the theory works, or to new discoveries, when it does not. WHY QUANTITATE? When I hear the word quantitation, what comes to mind is the con-trast between two famous 19th-century German scientists, Alexan-der von Humboldt and Carl Gauss, as described in Measuring th