Jeffrey S. Turner

In modern evolutionary theory, selection acts on particular genes and assemblages of genes that operate through phenotypes expressed in environments. This view, however, overlooks the fact that organisms often alter their environments in pursuit of fitness needs and thus modify some environmental selection pressures. Niche construction theory introduces a reciprocal causal process that modifies natural selection relative to three general kinds of environmental components: abiota, biota (other organisms), and artifacts. The ways in which niche-constructing organisms can construct or modify the components differ. Modification of abiota, for example, may have different consequences from the construction of artifacts. Some changes in abiota may simply be caused by the by-products of metabolisms and activities of organisms. Alternatively, artifacts may be “extended phenotypes” that demonstrate obvious prior “design” and “construction” by organisms in the service of fitness needs. Nevertheless, adaptation should always account for the reciprocity between constructed niches and the living agents that construct them. Looking to well-adapted nature for inspiration for human-built artifacts must account for this reciprocity between phenotype and constructed environment as well as the novel features of human architecture, including frank intentionality of design and novel culturally acquired knowledge.

Darwinian evolution, as it was first conceived, has two dimensions: adaptation, that is, selection based upon “apt function”, defined as the “good fit” between an organism’s metabolic and biological demands and the environment in which it is embedded; and heredity, the transmissible memory of past apt function. Modern Darwinism has come to focus almost exclusively on hereditary memory, eclipsing the—arguably still-problematic—phenomenon of adaptation. As a result, modern Darwinism retains, at its core, certain incoherencies that, as long as they remain unresolved, preclude the emergence of a fully-coherent theory of evolution. Resolving the incoherencies will involve clarifying the relationship between embodied memory and apt function. In short, adaptation is a problem of semiotics: the organism must interpret the environment to fit well into it. This is well-illustrated by the constructed environments built by colonies of social insects, such as hives or nests, and the ancillary structures that contain them, forming an organism-like system known as a superorganism. The superorganism is marked by a kind of extended physiology, in that these constructed environments often serve as adaptive interfaces between the nest and ambient environment, and are constructed to manage the matter and energy flows between environments that constitute the process of adaptation. These constructed environments are also semiotic phenomena: interpretive structures, governed by information flow between the member insects and the structures they build. I review our findings on one such example: the mounds built by the fungus-cultivating termites of the genus Macrotermes. These structures are dynamic forms that are sustained by flows of soil from deep horizons up into the mound. The form, and hence the function, of the mound is determined by several environmental cues, most notably water and wind, as well as how termites interpret these cues, and signals that flow between termites, both directly and vicariously through the structures they build.