From the previous chapters, we see that (1) superdiffusion optimizes search efficiencies under specific (but common) circumstances and that (2) many animals move superdiffusively. Assuming these two facts, does it follow that there is a causal relation between them? Lévy strategies indeed optimize random searches, but does it necessarily follow that selective pressures systematically forced organism adaptation toward this optimal solution?
This is an important question because an adaptive pathway toward an optimal solution can prematurely stop at some suboptimal point that decreases the selection pressure on this particular feature to a level below the selective pressures on other issues . Biology and physiology are replete with suboptimal solutions. The classic example is the structure of the human retina, which has blood vessels on the wrong side of the photosensitive layer . Compromise solutions arise because adaptation (1) includes a stochastic component, (2) has to build on preexisting designs, and (3) occurs in a complex field where other pressures may be present and may possibly be stronger.
Dolphins, in the context of (mammalian) swimming adaptations, perform well, but how can we know whether or not their shape represents an optimal design? Some species of shark may have an even better hydrodynamic shape. Also, why did dolphins return to the ocean when selective pressures were pushing for improved terrestrial adaptation? The complex evolutionary history of real organisms contains many such contingent situations, such as changing selective pressures, genetic drift, low-number bottlenecks, and rare catastrophic events.