A stimulating investigation of new perspectives on gene effects, this sequel to The Selfish Gene argues that since genes can be said to have extended phenotypes outside the body in which they sit, we will have to revolutionize our views of evolutionary adaptation. It also looks at the theory of evolutionary stable strategies, the relationship between Darwinian and Lamarckian theories of adaptation, and Dawkin's suggestion that some of the surplus DNA in eukaryotic genomes may be parasitic.