River out of Eden

River Out of Eden

River out of Eden is a book that focuses on Charles Darwin's theory of evolution. It's author, Richard Dawkins has also written other books on evolution such as The Selfish Gene, The Blind Watchmaker, and The Extended Phenotype. In the book River Out of Eden, Dawkins relates life to being a river of genes that flows through time and how genes use organisms as temporary bodies to live in. So even when an organism dies, the genes live on through the offspring.

One of the first claims Dawkins makes is that every organism that has ever lived can look back at their ancestors and know that not a single one of their ancestors died in infancy. Every ancestor made it to adulthood and had procreated at least once in their lifetime. All of us can proudly say we are the product of an unbroken chain of successful ancestors all the way down the line to the first single-celled organism.

Another claim Dawkins makes is that all living organisms in nature have inherited good genes from successful ancestors. He is going on the theory that success of an organism is measured by its ability to survive and reproduce. Each generation can be thought of as a sieve that filters out all of the bad genes that have been replicated or mutated. Good genes fall through the sieve into the next generation of organisms, and the bad genes are filtered out. This theory can explain why organisms become better at the everyday tasks that are required to succeed in life.

Using the sieve theory, Dawkins argues that an organism is no more than a temporary body in which a set of companion genes work together towards a common goal - which is to grow the organism into adulthood, before they go on their own separate ways in the bodies of the organism's offspring. So, temporary bodies are created and discarded, but quality genes live on forever as they are perfectly duplicated and passed onto the next generations.

In the process of meiosis, "immortal" genes find themselves sharing temporary bodies with different sets of intimate companion genes in successive generations of organisms. Because of this, we can say that genes flow in a river through geological time. However, the river of genes can fork into two branches - caused by the geographical separation between two populations of organisms. For example, when half of all of the grey squirrels in Europe move to America - the American squirrels will adjust to the climate and all of its surroundings eventually causing a change in the species--- which will ultimately make the American squirrel and the European squirrel incompatible with each other. Organisms created by the two branches will form separate, non-interbreeding species, completing the process of speciation.

When discussing Africa and the tracing of human lineage back in time, Dawkins relates the ancestry model as genes flowing through a river of time. The ancestor gene flows down the river either as perfect duplicates of itself or as a slightly mutated descendent gene. While organisms have ancestry graphs and progeny graphs by way of sexual reproduction, a gene has a single chain of ancestors and a tree of descendents. Using any gene in the body of an organism, we can trace a single chain of ancestor organisms back in time, following the lineage of the one gene.

We can also trace human ancestry with a single chromosome, because a chromosome contains a set of genes and is passed down to the offspring via independent assortment from one of the two parents. However, chromosomal crossover mixes genes using non-sister chromatids from both parents during meiosis, which will tangle up the ancestry path.

In the later chapters, Dawkins shows how natural selection