Varieties of Action Systems
The functional systems discussed in chapter 5 were said to enable organisms to use important resources in their environment. But there are many different kinds of resources and, hence, there can be selection pressure for an animal population to develop a diversity of functional systems. For example, it has already been noted that information is significantly different from other kinds of environmental resources, requiring an entirely different mode of activity--exploratory, not performatory--for its use. The purpose of this chapter is to describe some of the most common types of action systems found among higher animals and their evolutionary background.
However, prior to analyzing all the diverse kinds of action systems we can find, it is useful to describe the evolutionarily basic functional system on which all the action and perception systems rest; that is, to identify those regulations common to most animals and that are required for any functional activity to proceed successfully. Are there any evolutionarily primitive forms of regulation out of which most, if not all, other kinds of activities have evolved?
To the extent that even the simplest eumetazoa tend to exhibit some local differentiation of anatomical features--such as a mouth (or feeding tube) and an anus, or a dorsal versus ventral side of the body--this has created one mode of selection pressure that has remained strong, constant, and fundamental for more than half a billion years. This is selection pressure for being capable of orienting a mobile body with distinct and (sometimes) mobile parts to the environment as a whole. For exploratory activity to proceed smoothly, the head and any organs within it must be geared to sources of environmental stimulation. For locomotion to proceed smoothly, any local movements of body parts must be carried out in such a way, and with such compensatory movements, as to not disrupt the locomotor path. For life itself to be maintained, a locomoting organism has to monitor the reactive forces of its environment (current, friction, impact, gravity) and to compensate for these if and when they exceed safe limits. With very few exceptions (mostly highly specialized parasites), part of what it means to be a multicellular animal is that this set of selection pressures will have had a powerful impact in shaping both body and behavior.
All these functions have their origin at the dawn of eumetazoan life, although subsequent evolution has in many cases made the functions more complex. This suite of functions, which involves both performatory and exploratory activity, I call the basic