While I was on holiday recently I went on a bit of a reading marathon, which included The Ancestor's Tale, by Richard Dawkins. I just can't recommend this book enough - unless you are a wizened old Biology professor you aren't going to know all of the cool and fascinating things in this book, but you should! Especially in these times of madness where Intelligent Design creeps insidiously through the minds of many. It is literally dripping with footnotes and references to Dawkins's other works and those of other authors (including, obviously, The Origin of Species). The book starts out in the present day and traces back through time, examining each of the points where major groups of species join into our ancestry. This is an entirely arbitrary way to look at it, but avoiding going forward in time removes any problems with language suggesting that there is intent or purpose in Evolution; And it is more convenient to consider us as the main line because we are humans, but the early chapters make it abundantly clear that the structure is humanocentric because it has a human author and that there can be no suggestion that Evolution was leading towards us. One of the most fabulous concepts in the book is actually quite generalised and applies to many areas outside Evolution; It relates to how we view things as discrete objects/groups and dislike gradiated scales (e.g. we like to label people black or white when in reality there is a full range of skin tones and a "black" person can have lighter skin than a "white" person). Dawkins refers to this as The Tyrrany of The Discontinuous Mind and I think it's a very interesting way of looking at things. Sadly this book is not for the faint-hearted, it's a pretty weighty tome and isn't shy about using Biological terminology (almost always with an excellent explanation though). Trust me that it's worth wading through and buy a copy!