The Extended Phenotype

Dawkins considered this his most important book, yet it is far less read than The Selfish Gene.

The central argument: an organism's phenotype does not end at its skin.

The beaver's dam, the caddisfly's case, the snail's shell modified by a parasite -- all are expressions of genes reaching outward into the environment.

This insight connects directly to niche construction theory, which Laland, Odling-Smee, and Feldman would formalise two decades later.

For anyone thinking about how organisms reshape the conditions of their own selection, Extended Phenotype is where the thread begins.

It is also a harder, more philosophical book than its predecessor, and rewards the effort.