Professor John H. Holland's book-length essay on how new and unexpected things happen when complex systems interact with one another, is essential reading for anyone having an interest in complexity science. Much of what Prof, Holland writes about occurs at the lowest level of life forms, arising from interaction of the basic structures of life itself, most often found at the cellular level, but extending into complex systems that are self organizing, and readily adapt into specialized organs and other structures of living things, whether plant or animal. It's a fascinating topic that is not well understood. This book stands as a companion to the author's other book that I have reviewed, Hidden Order, both of which I read in tandem. I highly recommend each of them, preferably read together, that will give readers a much more comprehensive understanding of the subtleties that play themselves out, whether they are outcomes of biological or biochemical interaction, the growth and development of organisms and structures within living things, or the way in which plants and animals at every level of life interact with one another in response to each other and the environment in which they live and thrive.The important thing to remember is that these are all stochastic processes that deal with aggregates, interacting with other aggregates, at different levels of a nonlinear complex system, in which accurate predictions cannot be made. Nevertheless, Prof. Holland's excellent book is a monumental step forward (at least for me) and explaining the fundamentals of complexity science. I highly recommend it.