The entity or characteristic A is causally upstream of the entity or characteristic B, A having an effect on B. An entity corresponds to any biological type of entity as long as a mass is measurable. A characteristic corresponds to a particular specificity of an entity (e.g., phenotype, shape, size).

Holds between materal entities a and b if the activity of a is causally upstream of the activity of b, or causally upstream of a an activity that modifies b