Modular Biological Complexity

It has been argued that the technological capability to fully simulate the human brain on digital computers will exist within a decade. This is taken to imply that we will comprehend its functioning, eliminate all diseases, and "upload" ourselves to computers (1). Although such predictions excite the imagination, they are not based on a sound assessment of the complexity of living systems. Such systems are characterized by large numbers of highly heterogeneous components, be they genes, proteins, or cells. These components interact causally in myriad ways across a very large spectrum of space-time, from nanometers to meters and from microseconds to years. A complete understanding of these systems demands that a large fraction of these interactions be experimentally or computationally probed. This is very difficult.