River Out of Eden - The Digital River

The Digital River

Further information: Gene-centered view of evolution, The Selfish Gene

Dawkins begins the book with a startling, yet true, claim on behalf of all organisms that have ever lived: not a single one of our ancestors died before they reached adulthood and begot at least one child. In a world where most organisms die before they can procreate, descendants are common but ancestors are rare. But we can all claim an unbroken chain of successful ancestors all the way back to the first single-celled organism.

If the success of an organism is measured by its ability to survive and reproduce, then all living organisms can be said to have inherited good genes from successful ancestors instead of less successful contemporaries. Each generation of organisms is a sieve against which replicated and mutated genes are tested. Good genes fall through the sieve into the next generation while bad genes are weeded out. This explains why organisms become better and better at whatever it takes to succeed, and is in stark contrast to Lamarckism. Successful organisms do not and cannot refine their genes during their lifetime. Rather, good genes make successful organisms which perpetuate good genes themselves.

Following this gene-centered view of evolution, it can be argued that an organism is no more than a temporary body in which a set of companion genes (actually alleles) cooperate toward a common goal: to grow the organism into adulthood, before they part company and go on their separate ways in bodies of the organism's progenies. Temporary bodies are created and discarded, but good genes live forever in the form of perfect replicas of themselves, a result of high-fidelity copy process which is typical of digital encoding.

Through meiosis (sexual reproduction), immortal genes find themselves sharing temporary bodies with different set of intimate companion genes in successive generations of organisms. Thus genes can be said to flow in a river through geological time. Scoop up a bucket of genes from the river of genes, and we have an organism. Even though genes are selfish, over the long run every gene needs to be compatible with all other genes in the gene pool of a population of organisms, in order to produce successful organisms.

A river of genes may fork into two branches, mostly due to the geographical separation between two populations of organisms. Because genes in the two branches never share the same bodies, they may drift apart until genes from the two branches become incompatible. Organism created by these two branches (or two rivers) will form separate, non-interbreeding species, completing the process of speciation.