 The mathematical-oriented outcome-only definition of drift is often associated with the so-called “statisticalist” approach to evolutionary theory, but since it is simply a definition of drift and not a metaphysical thesis it need not be. For example, a non-statisticalist could consistently hold that natural selection is causal (and thus, evolution would not be purely statistical, as it is on the statisticalist interpretation), but that drift occurs when and only when there is a deviation of the actual outcome from fitness expectation. Indeed, Frédéric Bouchard and Alexander Rosenberg (2004) seem to hold such a view. The intersection between issues of drift and the debates over statisticalism will be discussed further below.