This book introduced me to 'reaction norms' and 'phenotypic plasticity.' Believe me, these are critical notions for any discussion of evolution. Phenotypic plasticity is the notion that different environments produce different phenotypic expressions despite identical genetic material. The book discusses a variety of cases pulled from the animal and plant kingdom. For example, many plant have develop into different 'forms' depending upon the altitude of their environment. In the animal kingdom, twin spiders will build different types of webs depending upon their environment. The 'reaction norm' represents the 'normal' phenotypic response to the environment, something we often mistake as being the genetic 'design.' The book covers the somewhat daunting topics of allometry, ontogeny and epigentics, but does so in a very readable way. The books is accessible to the interested scientific reader regardless of background. Additionally, the book includes brief historical outlines of major lines of evolutionary thought. These provide an alternative avenue for accessing the theory when the terminology gets difficult. In short, its the best reference on evolutionary theory I've found.