 This later statement is in many ways similar to the earlier one, but there are some crucial differences in the formulations. According to the later article, the different individuals must be within the same species, and it is phenotypic variations, rather than fitness, that must be inherited. Many authors have echoed Lewontin’s influential principles (see Godfrey-Smith (2007) for a thorough review); for markedly different approach to formalizing the theory, see Tennant (2014)).