River Out of Eden: A Darwinian View of Life is a 1995 popular science book by Richard Dawkins.
The King James Version reads "And a river went out of Eden to water the garden; and from thence it was parted, and became into four heads."
The first chapter lays down the framework on which the rest of the book is built, that life is like a river of genes flowing through geological time where organisms are mere temporary bodies.
The second chapter shows how human ancestry can be traced via many gene pathways to different most recent common ancestors, with special emphasis on the African Eve.
The fourth chapter describes the indifference of genes towards organisms they build and discard, as they maximise their own utility functions.
The last chapter summarises milestones during the evolution of life on Earth and speculates on how similar processes may work in alien planetary systems.
Dawkins begins the book by stating that all our ancestors reached adulthood and begot at least one child before they died.
Bodies are created and discarded, but good genes live on as replicas of themselves, a result of a high-fidelity copy process typical of digital encoding.
Dawkins shows that this approach is misguided, as the numbers of ancestors and descendants seem to grow exponentially as generations are added to the lineage tree.
If we start with all humans alive in 1995 and trace their ancestry by one particular gene (actually a locus), we find that the farther we move back in time, the smaller the number of ancestors become.
But genetic recombination (chromosomal crossover) mixes genes from non-sister chromatids from both parents during meiosis, thus muddling the ancestry path.
Creationists often claim that some features of organisms (e.g. resemblance of Ophrys (orchid) to female wasp, figure-eight dances of honeybees, mimicry of stick insects, etc.)
Gulls' hard-wired instincts make them reach over and roll back not just their own stray eggs, but also wooden cylinders and cocoa tins.
The same principle can be applied to the distance between prey and predator, to the angle of view, to the skill or the age of a creature, etc.
In addition to demonstrating how gradual changes can bring about features as complex as the human eye, Dawkins states that computer simulation work by Swedish scientists Dan Nilsson and Susanne Pelger (although it is not a computer simulation but simple mathematical model) shows that the eye could have evolved from scratch a thousand times in succession in any animal lineage.
In Dawkins' own words, "the time needed for the evolution of the eye... turned out to be too short for geologists to measure!
Dawkins quotes how Charles Darwin lost his faith in religion, "I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of Caterpillars."
Dawkins rephrases the word purpose in terms of what economists call a utility function, meaning "that which is maximised".
Dawkins uses this technique to reverse-engineer the purpose in the mind of the Divine Engineer of Nature, or the Utility Function of God.
In nature, only genes have a utility function – to perpetuate their own existence with indifference to great sufferings inflicted upon the organisms they build, exploit and discard.
If there is ever a time of plenty, this very fact will automatically lead to an increase in population until the natural state of starvation and misery is restored.In the last chapter, Dawkins considers how Darwinian evolution may look outside planet Earth.