Second, DST theorists have often endorsed a “parity thesis”: genes play an indispensable role in development, but so do other causal factors, and there is no reason to privilege gene’s contribution to development. This claim is often buttressed by reference to Richard Lewontin’s arguments for the complexity and context sensitivity of developmental interaction, and his consequent arguments that we cannot normally partition the causal responsibility of the genetic and the environmental contributions to specific phenotypic outcomes (Lewontin 1974, 2000). DST theorists think that informational models of genes and gene action make it very tempting to neglect parity, and to attribute a kind of causal primacy to these factors, even though they are just one of a set of essential contributors to the process in question. Once one factor in a complex system is seen in informational terms, the other factors tend to be treated as mere background, as supports rather than bona fide causal actors. It becomes natural to think that the genes direct, control, or organise development; other factors provide essential resources. But, the argument goes, in biological systems the causal role of genes is in fact tightly interconnected with the roles of many other factors (often loosely lumped together as “environmental”). Sometimes a gene will have a reliable effect against a wide range of environmental backgrounds; sometimes an environmental factor will have a reliable effect against a wide range of genetic backgrounds. Sometimes both genetic and environmental causes are highly context-sensitive in their operation. Paul Griffiths has emphasised this issue, arguing that the informational mode of describing genes can foster the appearance of context-independence: 