The Selfish Gene is a landmark 1976 work in the field of biology: It puts the gene at the center of the process of evolution and explains how, when this is taken into account, genes must be seen as “selfish.” Author Richard Dawkins then uses this theory of gene selfishness to explain the massive variety of animal behavior observable on Earth.
Evolution occurs through differential survival: in a given population of entities with differing abilities, some survive and propagate while others die out.
But contrary to what is often thought, the basic units that evolution acts on are not individual organisms but genes: short snippets of DNA, the replicator molecule that is the basis of all life on Earth.
The reason for this is that genes fulfill an important criterion that evades individual organisms: genes are not unique and can exist as copies in many different bodies. For example, all blue-eyed people have in their cells a copy of the gene for blue eyes.
Most organisms, on the other hand, cannot replicate themselves as identical copies. This is because sexual reproduction does not produce copies but rather combines the parents’ genetic makeup to create new, unique individuals.
The fact that genes exist as copies makes them near-immortal. While individual organisms tend to survive for no more than a few decades, genes can live for thousands or even millions of years. Consider that while your ancestors are long dead, you no doubt carry plenty of their genes in your cells and will in turn pass on at least some of them to your descendants.
It is the genes’ multiplicity and potential for immortality that makes them candidates for evolution to act upon.
The basic unit of evolution is the gene, because it can exist as multiple copies and is therefore near-immortal.