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       In evaluating our evolving view of the nervous system, I imagine that there are several major benefits of a system that can generate outputs without the need for inputs. I am specifically approaching this issue with an evolutionary perspective. Firstly, I would think that the need for internal generation of stimuli is critical to maintaining a daily rhythm. Suppose, for example, that our nervous system only reacted when prompted with an input. If we were sleeping in a dark silent cave, could we sleep indefinitely until awoken by some stimulus (a bear entering the cave, or someone attacking us)? Clearly we cannot sleep indefinitely, and this daily cycle must be tied to internal stimuli. Devoid of any external stimuli, we still wake up (albeit after perhaps more sleep than we might normally get). These rhythms—Circadian rhythms—keep us functioning even without external stimuli. (Check out this cartoon). This cyclic rhythm presents evolutionary benefits in that we can meet our body’s needs in a timely and efficient manner. What if we had no idea when we would be hungry or tired? It would be impossible to plan anything. If you just became overwhelmingly hungry at random times that were not governed by some internal stimuli, it would be very difficult to survive as a hunter/gatherer (or pretty much anyone for that matter, aside from perhaps someone who lives in a supermarket).

       So what other benefits does this “spontaneously generating” nervous system present? It offers us the ability to adapt to new situations and environments. If we could only output based on input, we would be greatly troubled by a new situation. If an input came along that was totally foreign to us, what would we do? While some pathways of response are heavily-traveled highways of the nervous system, (eg- the fight or flight mechanism, or rest and digest), we will certainly be presented with new challenges and the outputs they will demand.

       One other evolutionary benefit would be that it allows us to avoid predation that might normally capitalize on routine. Consider the case of an unlucky mouse who was born with a very primitive nervous system. Whenever cheese was dropped on the floor, he immediately (and always) responded by running out to get the cheese. Furthermore, assume he only ran out of his hole when the cheese was dropped. A cat might notice this pattern and capitalize on his prey’s primitive ability to process inputs and outputs. The next time the cheese dropped on the ground, that cat might be waiting for the mouse. My point is that our ability to generate internal stimuli and operate in a non-prescribed manner is a critical element of defense from predators.