This series begins with The Machine in the Ghost

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Can understanding the motivations of natural organisms help us make artificial organisms?

What is motivation?

We sometimes attribute a machine or other thing with having 'a mind of its own'. We tend to do that when frustrated by the behavior of something that we think we should be able to control, or at least accurately predict how it will behave. But the kernel of truth under that anthropomorphic exaggeration is that we tend to associate mind with behavior that is complex, unpredictable and maybe even impossible to understand. To say we don't understand the behavior of something means that either its motives are hidden from us or the thing acts under some magical will that is outside of physics altogether, and thus inherently unknowable.

What determines, accounts for or explains the tendencies in an organism's behavior? Why does an organism act in the particular way it does at a particular time? Even asking this question implies that behavior is caused or determined by factors that can be known to some degree. What things motivate behavior?

Let's consider the meaning of motivation before trying to answer that question. We want to avoid being pulled in unproductive directions by the semantic inertia of well-established yet vague and abstract terms when we attempt to use them in the precise descriptions of science and engineering. First, the concepts of motive and motion share the Latin root for movement. Basically, motivation means making something move. In ordinary talking, we generally use 'motivate' and 'motivation' to mean something like 'influence a person to act to achieve a particular purpose'. Managers, for example, try to motivate workers to do their assigned work effectively and efficiently. Motivate in that sense seems to imply influencing a person's thinking so that the assigned task becomes the person's own goal, rather than simply coercing the person to some desired behavior by threat some alternative unpleasantness. What is entirely clear is that motivating people is tremendously more complex and much less deterministic than motivating a pool ball to enter a pocket, triggering viral reproduction, or training a dog to a desired behavior. Motivation becomes more complex as behavior becomes more complex. This suggests that an organism's motivation be understood as effects on an overall control system that grows out of simple reflex and is ultimately deterministic, but which is susceptible to chaotic limits on predictability at high levels of complexity.

Definition: Motivation is the collective internal and external effects on an organism's behavior control system.

Motivation in Natural Things

Life ranges in complexity from the simplest one-cell organism up to Homo sapiens sapiens, the modern man animal. The complexity of the behavior that life exhibits parallels its physiological complexity, and the most interesting behavioral diversity comes with the development of the central nervous system and brain. To get a handle on motivation and its role in the behavior of natural organisms, and hopefully form some ideas that can be applied to motivation design for artificial organisms, let's take a quick look at some things that are alive, or at least almost alive.

Sub-life

Until relatively recently, virus-like things were considered to be alive, mostly because they are constructed of complex organic stuff like proteins, they have RNA or DNA, and they replicate in certain situations. We have refined our concept of life, and those types of things are not considered to be alive now because they are not cells and they have no metabolism. They are as inactive as rocks until they by chance bump into the right kind of cell that triggers their one simple behavior, which is to release their genetic material so that the host cell will makes many copies of them.

Does it make sense to say a virus is in any way motivated? We can see what looks like a purpose, an action and a result (reproduction, invasion of a cell and many copies of the original virus.) We may be tempted, out of laziness, to say the virus 'wants to reproduce' and that it 'attacks' a cell and 'reproduces'. Some complex viruses like the well-known T-4 bacteriophage (the bacteria-eater that looks like a moon lander) do exhibit a very mechanical and deterministic kind of real behavior. They actively inject their DNA into a bacterium through the cell membrane when they chance to land on one. Their 'action', however, is much like a spring-loaded syringe; it has a specific trigger and is a single, self-destructive event that is not repeated. We can't even call this behavior a reflex. It's very clear that a virus doesn't really 'do' anything and it certainly can't want anything. It has no range of behavior and it is entirely passive. Just like a rock no interesting behavior and no motivation.

Low Life

When we look at pond water under a microscope, we see all kinds of things that are obviously alive. Some of them aren't very visibly active; they just grow slowly and make more of themselves through asexual or sexual reproduction. Others lead more dramatic lives of scurrying around to eat or to not get eaten. Behavior here is somewhat complex. It seems to be driven by purpose and is characterized by adaptive activity. Even simple single-cell animals like the paramecia and amoeba have compound avoidance (phobic) and seeking (philiac) behaviors upon which their success depends. If an amoeba finds itself floating freely in a liquid, it will stretch out fingers to find a surface. If a finger does find a surface, it sticks and pulls the rest of the amoeba to it. A paramecium spends a lot of its time swimming around. If it bumps into something, it will reverse direction for a moment and then push forward again in a slightly different direction.

That behavior is repeatable and very predictable. It is reliably consequent to specific stimulations provided by the organism's environment. All of this activity is accomplished with no nervous system at all. What motivates such complex behavior in such relatively simple creatures?

Consider the paramecium obstacle avoidance behavior in more detail. The paramecium has three movement modes, which are swimming forward, swimming backward and resting. The swimming direction depends on one factor, which is the cell's electrical potential. When a paramecium bumps into something, the electrical potential changes and the swimming direction reverses. In a short while, the cell potential returns to normal and the animal begins to swim forward again. So even though the paramecium is a living organism and it exhibits a behavior that seems intentional and purposeful to an observer, this behavior is very deterministic. The difference we see here from the simpler mechanical-chemical behavior of the virus that we considered earlier is that the living organism has variable internal states that combine with external (environmental) states to determine a specific behavioral response from the organism's repertoire of actions. We can call those internal and external states motivation.

The chemical signaling mechanisms that produce cell behavior, such as the paramecium behavior I just described, are the most primitive and most basic determinates of behavior. Even in organisms controlled by the most complex nervous systems, it is at the chemical/mechanical cell signaling level where the rubber meets the road. The nervous system is a specialized multicellular system of control that is stimulated through the mechanism of cell signaling, works through cell signaling and acts directly through cell signaling to effect complex organic behavior.

Higher Life

Much of the direct research on the functioning of nerve cells and natural neural networks has been done on creatures such as the sea slug, the leech, the squid and the lamprey. That is because these animals have large neurons whose activities are easily measured. They also have relatively small and simple nervous systems to which a relatively small set of behaviors can be fully mapped.

The results from the extensive work done on behavior control in the leech is illustrative. In it's natural environment, an aquatic leech exhibits a small list of compound behaviors.

• Contract the whole body when touched on the head or in the presence of noxious stimulants.
• Swim or crawl when touched on the sides or tail.
• Hang out at the water surface and move in the direction of waves in the water.
• Explore a warm body.
• Feed when certain chemicals are detected in the presence of warmth.
• Mate.

Those macro-behaviors are all built on the micro-behaviors of individual muscle contractions that are caused by specific nerve cell output. They are all induced by the stimulation of sensory neurons. Some of these behaviors conflict with others. The contraction reaction prevents swimming or feeding. If you touch a swimming leech, it will contract reflexively and interrupt its swimming. If you touch a hungry feeding leech, however, it will continue to feed until sated. The behaviors have a priority structure, and the priority can shift according to the animal's internal states.

We might group those six behavior patterns into the high-level goal categories of defense, sustenance, and reproduction. We could further group those into activities of survival and reproduction, which we might call the ultimate motivations of living creatures. We might then say that the animal is swimming to flee harm or lurking on the water to hunt for prey, or mating to reproduce.

But if we do, we have fallen into the semantic trap of assigning intention to effect. The leech does not intend to reproduce any more than does the virus. It does not choose to contract a certain set of muscles in a certain timed sequence in response to specific stimuli any more than an eight ball decides to move into the corner pocket when hit the right way by the cue ball. Even though the interplay of the animal's behavioral repertoire, the environment and the animal's own internal states produces patterns of activity that are complex enough and non-obvious enough to appear as actions of a very simple mind, the leech has neither mind nor intentions. It doesn't even have a brain as such, but two mini-brains, one for the front end and another larger one for the tail. It is 'merely' a marvelous system of sensing, control and effective action that happens to result in prolonged survival of the individual and its species in a dynamic and hostile environment where food is scarce. It is what it is because a lot of micro-behaviors have come to be coordinated in ways beneficial to it by an adaptive nervous system. What motivates the leech's behavior is much like what motivates the much simpler animals considered above, which is to say internal and external states. What sets higher creatures apart from lower creatures is the much larger repertoire of complex behaviors that can respond more flexibly to a wider range of environmental change. Both of those qualities are the gifts of a more complex nervous system.

Humankind

Going from virus to leech to human is to take breath-taking leaps across the range of complexity in natural things. Of course it would be extremely interesting and informative to map the parallels between nervous system and behavior in very small steps over the full range of things, but here we are just trying to establish a rough continuity in what constitutes motivation across that range.

Humans have the most complicated nervous system of any known living creature and our behavior is correspondingly complex. What things motivate human behavior, and how is it different from the lower animals we've considered so far? One special feature of our own complexity that may either greatly aid or grossly distort our study of human motivation is our self-awareness. We know what it is like to be us, in some sense or other. How much we can rely on introspection to understand our individual motivations and the general motivations of our kind is, I think, a very open question. The safe-side assumption is that we must regard introspection as perhaps indicative, but incomplete and unreliable when it comes to identifying complex motivations. On the other hand, much of the objective experimentation that yields important results for the lower animals like the leech involves vivisection, maiming and killing, and cannot conscionably be applied to humans or the higher animal under normal circumstances.

In spite of the special problems that face scientific enquiry of the neurological basis of human behavior, we have come to know much already. Studies of trauma and disease that involve the nervous system have added much to our understanding over the decades. Particularly exciting are new technical developments such as functional magnetic resonance imaging (fMRI) , which lets researcher map some mental processes to areas of the brain in real time. One striking result from a recent fMRI study demonstrated that neural activity in the brain can predict a person's decision seconds before that person consciously makes the decision (Unconscious determinants of free decisions in the human brain. 
Nature Neuroscience, April 13th, 2008) . That result must be particularly astonishing to those who closely associate the self with consciousness and choice with conscious reasoning or a free will of some sort.

What we can reasonably expect, though, is that what is learned about motivation in the less complex animals will also apply to humans to the extent that our physiology is the same. We can also expect that whatever distinguishes our motivation can be explained by the differences in physiology, the additional complexity that nature has given us in additive layers. We should also note that those added layers are mostly evident in our brain structure. What makes our brains different, and perhaps better, than the brains of simpler creatures is not size or number of parts, but the addition of entirely new parts that have entirely different functions.

Overall, we must picture human motivation as a dynamic, and sometimes even turbulent, mix of many motives of different levels that may be conscious or subconscious and may compete or support each other under the influence of an ability to take possible futures into account as well as the past. High-level motivations that involve self-image, morals, and attitudes coexist in the mix with low-level motivations such a hunger, libido and the other homeostatic mechanisms.

This series begins with The Machine in the Ghost

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