  Natural selection, if it is to resemble the Darwinian concept that bears that name, must be reserved for reference to an interaction between a variable, heritable feature of an organic system and the environment of that system. That interaction may or may not change the proportions of those features across generations, and those proportions may change for reasons other than those interactions. But a plausible natural selection hypothesis must posit some such interaction. On this issue I will give the last word to Stephen Jay Gould: