Figure 5 Diagrammatic relations among relative phenotypic fitness, the number of phenotypic maxima or optima, and the coarseness of fitness-landscapes. As phenotypic complexity (i.e., the number of biological tasks to be simultaneously performed by organisms) increases, the relative elevation of fitness peaks declines, but the number of phenotypic maxima (or optima) and the coarseness of the landscape increase (A-C).

and accelerate evolution, particularly in very large panmictic populations (Wright, 1932). And fourth, all walks were assumed to be unfettered by genetic or development constraints. Even for plants, which arguably may be more phenotypically ''plastic" than animals, this is a naive expectation (Maynard Smith et al., 1985).

On the other hand, the approach taken here has some obvious strengths. First, walks were simulated over a dimensionally complex morphospace containing phenotypes representative of the entire spectrum of vascular land-plant morphology. Second, although only three were considered, the functional obligations elected to define and quantify fitness are biologically realistic for the majority of past and present terrestrial plant species. Third, although the environment, living and nonliving, is in constant flux, the particular episode of plant evolution focused upon here most likely was dominated by the operation of physical laws and processes. Metaphorically, the fitness-landscape of the first occupants of the terrestrial landscape was painted in the primary colors of biophysics rather than the subtle hues of complex



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