Fig. 1.

The causality of different levels in the evolution of sensory systems. The genome, which is the level directly subject to heritable variation, generates the morphology and physiology, which in turn generates behavior guided by sensory information, and this in turn generates the fitness that selection can act upon. In this view, sensory-guided behavior is entirely a consequence of the morphology and physiology. From this, it follows that genetic modifications are driven by modified requirements on the morphology and physiology, which in turn are driven by modified requirements on sensory-guided behavior and finally by requirements for improved fitness. This is different to the view of Endler (1992), who considers sensory organs and behavior to coevolve, but the sensory organs are then seen in isolation from the rest of the morphology and physiology of the organism. The two views are not in logical conflict, but the view illustrated here gives a more important role to behaviors, as the causal evolutionary link between fitness and sensory systems (which are part of the organisms’ morphology/physiology).