THE FABRIC OF ADAPTIVE LANDSCAPES: UNDERSTANDING THE EVOLUTION OF DIVERSITY AND DISPARITY FROM FIRST PRINCIPLES

Here, I use the notion of an adaptive landscape as the centerpiece of theoretical approach for understanding the interplay of ecology and development in the evolution of diversity and disparity.  The axes that define latitude and longitude of the landscape correspond to the different developmental rules that generate the morphology of a clade.  The elevation of the landscape at any given point represents the fitness of the morphology corresponding to that point. The number of peaks in the landscape, a function of its roughness, gives the maximum potential alpha diversity of the taxon with those particular developmental rules. Evolution proceeds as a Branching Monte Carlo Markov Chain (BMCMC), exploring the adaptive landscape, and extracting the morphological potential lying within the developmental rules of the clade, as dictated by the needs of the organisms.  Generally speaking, a morphological optimum for one need will not be optimal for another need (the Principle of Frustration).  Thus, the roughness of the landscape is determined by the number of at least partially conflicting needs of the organism, and the disparity of a clade is proportional to the roughness of the landscape.  Developmental constraint increases the roughness of the landscape, and thus increases both diversity and disparity.  For each need there is a minimum fitness needed to remain viable.  Thus, the landscape is bathed in an uneven sea; areas under water represent non-viable morphologies.  Changes in the environment do not change the topology or roughness of the adaptive landscape, but affect the sea-level on the landscape. In reality adaptive landscapes are highly dimensional, reflecting the complexity of the developmental rules that generate morphology.  They are also hierarchical in structure, with some dimensions hidden within others.  Recognizing this, escalation represents a change in the position of the adaptive peaks in the hidden (taxon-specific) dimensions, but not in the fundamental dimensions, which determine the basic body plans of the taxa.  Microevolution refers to evolution on a (relatively) unchanging adaptive landscape, while macroevolution refers to either evolution on a changing adaptive landscape, or comparisons between clades with different adaptive landscapes (e.g., those with different developmental rules, and needs).