The subtitle of this book points to an observation that most biologists will anecdotally agree with. Looking at the long sweep of evolutionary history, there is indeed a clear overall tendency for life forms to become more diverse and complex. Daniel W. McShea and Robert N. Brandon, the one a biologist with a secondary appointment in philosophy, the other a philosopher with a secondary appointment in biology, here declare it the Zero-Force Evolutionary Law or ZFEL. But is this a law of nature? And does it really differ from stochastic processes or even entropy?