Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

A further step in the evolution of mechanisms controlling the behavior organisms is the learned pattern of behavior, of which the conditioned reflex is a simple form. The neural systems of many kinds of animals are adapted so that, when a trigger stimulus for a specific unconditioned reflex is repeatedly accompanied or preceded by another stimulus, the organism will, after some time, also react by launching the particular behavior pattern in consequence of this other stimulus.  The famous salivating Pavlov’s dogs are a textbook example of an experimentally produced conditioned reflex.