Having already read some Richard Dawkins's works and knowing that "River Out of Eden" is his shortest book and the least technical one, I was initially reluctant to reading it, but it turns out it was well worth it.
Subtitled "A Darwinian View of Life", it is just that, with a bonus philosophical tint. Feeding on the ideas of Professor Dawkins's previous books ("The Selfish Gene", "The Extended Phenotype" and "The Blind Watchmaker"), this is a short volume, albeit dense in themes and thought-provoking, unlikely to allow you to easily let go of it until you have finished reading.
The first chapter, "The Digital River", rests atop the river metaphor. Starting with the obvious remark that every living organism is sure to have had an unbroken line of successful ancestors (i.e. ancestors that did not die before having at least one offspring that survived them), the author proceeds to explain that "It is not success that makes good genes. It is good genes that make success, and nothing an individual does during its lifetime has any effect whatever upon its genes". Thus the river of the title is "a river of DNA" that "flows through time, not space. It is a river of information, not a river of bones and tissues: a river of abstract instructions for building bodies, not a river of solid bodies themselves". Admirably sticking to this metaphor, Dawkins explains descent, heredity and speciation in this easy to comprehend style, turning later on to the differences between analog and digital transmission and showing why the DNA code can be regarded as digital information that gets passed down the generations.
In the second chapter, "All Africa and Her Progenies", the reader is introduced in the same non-technical manner to the concept of mitochondrial DNA - the DNA that is found in little cell organelles called 'mitochondria'. It is not reshuffled the way that nuclear DNA is at the moment of reproductive cells formation and can only be transmitted to children through the female line (since only the female egg is large enough to contain mitochondria that can divide and get passed down to the cells of the forming embryo). Thus, apart from the DNA found in the nuclei of every cell, there is this second line of descent, the mitochondrial DNA, tracing each individual's ancestry back to Africa, to a remote female ancestor poetically called "Mitochondrial Eve".
The third chapter, "Do Good by Stealth", uses many examples from nature to show how relative "perception" and behavioral patterns are across the living world. A few interesting experiments are described, along with their conclusions. For instance, for black-headed gulls, "a threatening neighbor is little more than a disembodied black face. No body, or wings, or anything else seem to be necessary". Turkey mothers attack anything that moves in order to protect their chicks, except for moving things that emit the sounds made by baby turkeys; alas, a deaf turkey mother killed its own offspring because even though they looked and moved like baby turkeys, it made no difference for the mother bird's perception, since all she relied upon was the hearing sense (which she lacked). Professor Dawkins then moves on to show the fallacy of the argument from personal incredulity and suggests along the lines a method of approach that can be employed to explain how "a device that must [seemingly] be perfect if it is to work at all" could evolve. The bottom line of the chapter is "Do good by stealth. A key feature of evolution is its gradualness. This is a matter of principle rather than fact. (...) Without gradualness in these cases, we are back to miracle, which is simply a synonym for the total absence of explanation."
The fourth chapter, "God's Utility Function", introduces the concepts of "reverse engineering" and "utility function" (the latter being the economical term describing "that which is maximized"). Applying these concepts to a few cases, such as the elaborate dance of bees, used to indicate the relative source and distance of food, the sex ratio in elephant seal populations and the evolutionary arms race between cheetahs and gazelles, this chapter also provides food for thought, showing that "We humans have purpose on the brain. We find it hard to look at anything without wondering what is it 'for', what the motive for it is, or the purpose behind it. When the obsession with purpose becomes pathological it is called paranoia - reading malevolent purpose for what is actually random bad luck. But this is just an exaggerated form of a nearly universal delusion. Show us almost any object or process, and it is hard for us to resist the 'Why' question - the 'What is it for?' question."
The book's fifth and final chapter, "The Replication Bomb", uses the supernova analogy to illustrate the many levels that need to be achieved by intelligent life forms that find themselves in this universe, taking note of it and starting to explore it, in search of other intelligent life. The first step in this process is "the Replicator Threshold itself: the arising of some kind of self-copying system in which there is at least a rudimentary form of hereditary variation, with occasional random mistakes in copying". Then a phenotype threshold will be needed, a replicator team one, a multi-cellular organism one, the high-speed information processing level, consciousness, language, cooperative technology, radio and finally space travel. The logical unfolding of this model is a very interesting read.
To conclude, I find "River Out of Eden" to be excellent for somebody having never read anything else by Richard Dawkins, but I urge you to buy and read this book even if you have read some of his other works. It is surprisingly inspirational (and even poetic, some might argue), while not burdening the reader with technicalities in the least. This book made it clear for me that Professor Dawkins's prose is an exquisite craft, indeed.