An orthodox stance would not recognize earthworm niche construction as an evolutionary cause but rather treat it as the outcome of earlier natural selection that favored earthworm soil-processing capabilities.
Implicit in this reasoning is the separation of the processes that generate variation (e.g., mutations in soil-processing activity) and the causes of fitness differences (e.g., the alternative environmental conditions that favored those mutations). This allows the explanation for the adaptive fit between earthworms and their soil environment to begin with that change in ancestral environmental conditions that generated selection for earthworm soil processing.
For instance, in the figure below, (1) a random mutation, (2) changes the earthworms’ soil processing, and (3) is selected because of beneficial effects on fitness.
In reality, because ancestral earthworm activity is itself the cause of the soil environment that favors mutations in soil processing, the causes of variation and fitness differences are not independent (bottom figure). The explanation for the adaptive fit between earthworms and their soil environment cannot begin with those ancestral external environmental conditions that elicited selection for earthworm soil processing, since those conditions were themselves products of earlier earthworm niche construction.
There is no longer a clean separation of selection and variation: these processes are causally intertwined. This confound is not resolved by pushing back the explanation to commence with an early episode of selection, as the selective environment is always partly constructed by organismal activities.
Worse, the processes underlying inheritance are also not independent of the causes of variation and fitness. The genetically specified propensity for soil processing that contemporary earthworms inherit only functions effectively as the source of earthworm adaptation to a soil environment because contemporary earthworms also inherit the ecological legacy of a modified soil environment that is the product of ancestral earthworm niche construction.
Traditionally, this causal interdependence has been neglected or downplayed. Recognizing niche construction as an evolutionary process is how niche construction theory builds causal interdependence into evolutionary explanation.
