Robert Skipper took issue with Dick Lewontin’s definition of natural selection. Skipper did not like how Lewontin removed the struggle for existence and interaction with the environment from the requirements for evolution by natural selection. John Hawks points out that the environment encompasses everything outside of the genome (the proteome, cell environment, extracellular physiology, the extra-organismal environment, and even culture), and I agree with him — as a reductionist, I like to view the nucleotide as the unit of selection and everything else as the environment. Skipper agrees, and thanks Hawks for the clarification. This is by no means an adequate summary of the exchange. Go read all three posts for a fun exercise in philosophical gymnastics.