One response to the parity thesis has been to accept the view that genes are just one of a set of individually necessary and collectively sufficient developmental factors, but to argue nonetheless that genes play both a distinctive and especially important role in development (Austin 2015; Lean 2014; Planer 2014). As noted above, perhaps the most promising suggestion along these lines is that genes exert a form of causal control over development that is universal, pervasive and fine-grained. Many features of the phenotypes of every organism exist in an array of somewhat different versions, as a result of allelic variation in causally relevant genes. No other developmental factor exerts control that is similarly universal, pervasive and fine-grained (Woodward 2010; Stegmann 2014). Thus Stegmann illustrates Woodward’s idea that genes exert specific control over phenotypes by contrasting the effects of intervening on, say, the quantity of polymerase on cell activity with intervening on the DNA template itself. Polymerase is critically causally important, but varying its concentration will modify the rate of synthesis, but not the sequences produced. That is not true of modifications of the DNA sequence itself, so the DNA sequence is more causally specific than polymerase.