titative, and the connections between the life and physical sciences are becoming deeper and stronger. As a result, the predictive power of biology is also increasing swiftly.

How biological research is carried out is changing rapidly, too. Biologists increasingly do their work using sophisticated instrumentation that is rooted in the physical sciences. For example, synchrotron x-ray sources are used to determine three-dimensional structures of proteins. Focused laser beams allow manipulations of single molecules. Functional magnetic resonance imagers map activated regions of the brain. Highly parallel data acquisition, such as the use of simultaneous measurement of the expression levels of tens of thousands of genes in DNA arrays, has become commonplace. Computers now play a central role in the acquisition, storage, analysis, interpretation, and visualization of vast quantities of biological data.

Modern biology is becoming more dependent on the physical sciences (chemistry and physics) and engineering in multiple ways. First, as the analysis of biological systems advances at the cellular and molecular levels, the distinction between the physical and biological sciences blurs, and essential biological processes are most fruitfully treated in terms of their physical properties. Second, as biologists deal with systems at a higher level of complexity, theoretical tools from other fields increasingly are required to deal with the many simultaneously interacting components of such complex systems. For example, exocytosis and endocytosis are basic processes common to all cells; they are ultimately understood in terms of the physical chemistry of membrane fusion and fission. Another pertinent example is the study of genetic networks responsible for developmental processes. Here many genes interact combinatorially in positive and negative regulatory pathways to generate the spatial and temporal patterns exhibited in the adult organism. Understanding development requires theories of how these patterns form; physics, mathematics, and engineering provide advanced tools for formulating and testing such theories.

The ways in which scientists communicate and interact are undergoing equally rapid and dramatic transformations. Data and software are shared extensively over the Internet. Different kinds of data (e.g., genes with the corresponding diseases in the database Online Mendelian Inheritance in Man, available at http://www.ncbi.nlm.nih.gov/omim) are becoming linked. Investigators throughout the world query vast databases (e.g., Genbank, available at http://www.ncbi.nlm.nih.gov/Genbank/GenbankOverview.html) daily to design and interpret experiments. Many laboratories host highly informative Web sites, which complement their published



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