Systems Biology: Understanding the Biological Mosaic

Just what is Systems Biology? The definition depends a great deal on whom you ask. Some define it as the natural follow up from years of genome sequencing and functional genomics: a more holistic and dynamic consideration of data in a ‘‘systems’’ context. Others see it as a scale-up of mathematical biology: mathematical models of small systems have been around for decades, and more data and faster computers now makes it possible to consider bigger ones. Still others see it as a merger of biology with engineering: it is possible to apply many of the principles that go into (say) circuit design to a biological system in a predictive way. No doubt it is all of these things, though being a new concept it probably still needs some time to find its feet. Indeed, at this point it is probably more of a philosophy than anything that one can easily nail down. But one thing is clear: its time has come. Most everybody agrees that a systems view of biology is greatly needed to make the jump between all that we know about individual molecules to what we can understand or predict about a whole system: to combine individual stones to make the complete mosaic. And indeed we are now making the first tentative and clumsy steps towards a holistic understanding of biological systems. This special issue of FEBS Letters is dedicated to this new and exciting field. We have taken a broad view and as a result