"The Selfish Gene," written by Richard Dawkins, presents the idea that genes are the primary units of natural selection. It argues that organisms are vehicles for their genes, which strive to replicate and propagate themselves. This perspective shifts the focus from the survival of the fittest individual to the survival of the fittest gene. Dawkins introduces concepts like memes, which are units of cultural evolution, similar to genes in biological evolution. The book emphasizes that behaviors, such as altruism, can be explained through the lens of gene survival, suggesting that seemingly selfless acts may ultimately benefit the individual's genetic legacy.