This approach is integrative because it focuses on the interaction or integration of parts in a functioning organism. Integrative biology may use typically reductionist methods, but in a philosophically holistic framework. These are not mutually exclusive goals. Much of the progress made by reductionist biology can be applied to reach the more inclusive goal of integrative biology. One the most fundamental methodological differences between reductionist and integrative biology is in models of causality.
Reductionist biology has a much more restrictive model of causality than does integrative biology.
For instance, the reductionist approach assumes that effects at organismal level can always be reduced to causes at the gene level. Models of causality in integrative biology are much more complex. The integrative model is one of multidirectional causality that traces causal threads within and between hierarchical levels, and through time. For instance, population dynamics and natural selection on individual organisms can determine which genes are replicated in future generations. Only one of many possible directions of causation is from gene to organism.