Many philosophical systems begin with the examination of how we know what we know, as with the Cartesian "I think, therefore I am." This often gets mired down in the dualistic notion that mind is somehow independent of the brain. Materialism rejects dualism, largely because idealistic and subjectivistic arguments lead to so many absurdities -- and because common sense and practical experience confirm a referential link between our perceptions and the external world. As we will see, there is a better argument.

Subjectivism and dualism have strong basis in the fact that perception is our only experiential "reality"; blueness, the fragrance of a rose, the distinctive "sound" of someone's voice or a haunting melody have no external physical reality, but represent qualitatively different external phenomena -- electromagnetic wavelength, molecular structure, and complex fluctuations in air pressure. Our entire mental life is a completely subjective experience, but perfectly real to us. As Gilbert Ryle put it (Miller, 1983, p. 60), there is no "ghost in the machine." The human experience of self, soul and mind are manifestations of neurological function, and not the independent, more mystical entities we naturally imagine. Two of Darwin's contemporaries, La Mettrie and Thomas Huxley (Reese, 1980, pp. 240, 290), had argued that there must be an evolutionary explanation for mental function; we find it today in information theory. (Did anyone ever point out that epistemology is information theory?)

Life depends on information in two important ways. First, it is information -- the genetic code. Secondly, most forms require information about their surroundings -- about food, about danger and about potential mates. From the simplicity of a single-cell organism for whom sensed ripples in its aquatic environment meant food (low intensity sensation) or danger (high intensity), evolution has done a remarkable job of expanding the range and quality of information that is available to us through our perceptions. Acting on them, the individual behaves appropriately vis-a-vis actual, external reality.

Perception has its limits, though. Noise, narrow focus, restricted magnification or range, spectral bandwidth limitations, coarse resolution, etc. are all problematic. In addition, we have developed quite a catalog of sensory illusions (Miller, 1983, ch. 3) to which we are susceptible. Like our values, our perceptions are reliable only to the extent that the circumstances match the environment in which they were evolved -- and from which we are long departed. They remain quite adequate

We know, then, that any organism of complexity requires information about its environment in order to survive. We know that such information arrives in the form of perceptions, which comprise the entirety of the organism's experience; the objects of perception cannot be experienced directly. Any awareness the organism may have, then, must regard the experienced perception as "real"; and further, the awareness itself, as direct experience, must also be "real." Mistaken subjectivism and dualism are natural states for any naive, self-aware organism in an evolutionary world.

One of evolutionism's most valuable products, then, is a refutation of subjectivist and dualist perspectives. The standard materialist argument for referential perception, based on the accumulated experience of an individual over a lifetime, is compelling. But it pales by comparison to the evolutionary explanation, which multiplies that single lifetime's experience by countless generations and describes the process by which perceptions came to exist.

The epistemological basis from which all of us begin, then, is a probabilistic, inductive, evolutionary one, and we can now see that even the most rigorous deductive system must rest on premises that are rooted in our inductively developed world view. And our world view is ...

Building our world view is the process of developmental psychology, requiring assimilation of information and adapting our view according to the information assimilated (Kagan & Segal, 1988, p. 264). This is a mental model-making process driven by expectations derived from past experience (Miller, 1983, p. 141) and cognitive dissonance when those expectations are not met (Kagan & Segal, p. 582) -- forcing us to refine our models or reject the new information. These models are probably created by what Michael Gazzaniga calls an "interpreter" (located in the dominant left hemisphere of right-handed persons), which automatically generates a logical explanation for our experiences (Gazzaniga, 1985). In evolutionary terms, our models are selected according to how well they match our experiences. Our collection of models covers every aspect of the world around us -- its objects and processes, whether real or imagined.

Metaphysics, which almost defies definition because of its history of widely disparate incarnations, has traditionally subsumed all beliefs about things supernatural, and usually includes beliefs about the forces behind nature as well. I would like to redefine metaphysics as "our collection of mental models," disposing of confusing tradition in favor of practical functionality. Significantly, this puts scientific theory firmly in the category of metaphysics, implying that philosophy and science can no longer be considered separate disciplines. Also, we find a necessary circularity in epistemology (Van Cleave, 1988a), which can only be practiced by adults whose metaphysics is largely complete: "We can't know anything until we've accumulated enough perceptions to flesh out the appropriate models -- at which point we can begin to wonder about perception, among other things. For human philosophers, metaphysics ... must precede epistemology, which must in turn support the original metaphysics -- or our models are suspect."

Our common-sense view of force and causality is developed experientially on the human scale, and is transitive: A subject acts on an object. As a result, it is natural for us to assume that every force issues from some agency, which has some purpose or intent for its issuance. The evolutionary view allows us to escape this teleology in two ways: first, by recognizing the nature of force as valence through the expansion of our sciences; second, by understanding the evolutionary process that led to humanity and our subjective style of thinking.

Parenthetically, the objective perspective is the goal of the scientist, and rightly so -- for subjective bias is the worst obstacle to learning; but there is no such thing as pure objectivity, for our every thought is the product of a subjectively developed metaphysics. This should serve as a warning against arrogance and complacency for those who have found their "objective truths."

Metaphysics becomes, essentially, the whole of philosophy, subsuming all other branches. Ontology becomes a sort of taxonomy of objects; cosmology examines physical processes; logic, linguistics, semantics and mathematics are model systems (based on set theory) for analyzing and communicating information with minimum distortion; aesthetics examines the various spinoffs of our pleasure mechanisms. I must defer detailed comment on these other branches of philosophy to another time.

There is an emerging evolutionary view of the brain -- both in terms of neurobiological development (Rosenfield, 1988) and neurological function (Gazzaniga, 1985). Brain imaging techniques (positron emission tomography and magnetoencephalography) show behavior that is consistent with an evolutionary model of brain development and function. What follows is my own conjecture:

Information from the senses is selectively filtered for importance (and possible reflex response) by the reticular system according to inherited and experiential cues. It is then routed selectively, according to its qualitative attributes, much as coins are directed through a coin sorting machine. Each attribute, exciting activity at its destination, causes associations with remembered experiences and thoughts that shared that attribute. Simultaneous processing of all sensory information allows the lymbic system to assign "co-temporality" to all attributes of current experience, by which they can be recalled as a group. Areas of the brain which experience a high level of activity grow new interconnections as a result, allowing an increase in conceptual "resolution." Connectons between physically separate but frequently associated areas of the brain are also strengthened. The result is a brain which, loosely guided by reticular and lymbic biases as to what is important, drifts in continual association among its parts, pursuing either widespread patterns (or networks) of simultaneously active loci or, alternately, "chains" of neural associations along interesting paths.

By analogy, the brain's development and function would be much like a city, with buildings representing synapses, roads representing neurological paths, and traffic representing neurological activity. A few buildings are built on what had been open country, placed strategically according to the lay of the land for optimum functionality. Roads are built to connect them, and the process of functional expansion continues according to the interactions among the buildings determined by their individual functions and the valences between them. Patterns of activity develop among frequently associated buildings, and patterns of patterns emerge as well, on increasingly complex levels. One special complex of buildings develops whose function is to monitor the activity of the most persistent of these patterns, and its "traffic reports" allow predictions of when specific patterns are likely to recur, which patterns are likely to excite others into activity, and what all of this means with respect to the entire city -- consciousness. Our brain is more complex than the largest megalopolis mankind will ever build, though I suspect its function in this simple analogy is quite similar. This basic model seems to account for all aspects of mental function: memory, analogy, prediction, speculation, contrast, analysis, opinion, etc.

The complexity of our cerebral cortex is the single most important adaptation in our evolutionary history. Originally valuable because it allowed us to verify or override the evaluations of our lymbic system, to choose among them when they conflicted, and to imagine consequences of our actions in the increasingly remote future, it has now allowed us to understand the origin and function of those lymbic values ... and to question whether they truly apply to us today, either in specific situations or as general guides for behavior. These lymbic evaluations, or "epigenetic rules" (Ruse & Wilson, 1986) are the basis of our social structures and the ethics that surround them.

I am convinced that the degree to which we rely on epigenetic rules is a major determinant of human temperament and personality; the other primary contributors are the relative preference for the right or left forebrain and the influence of our somatosensory cortex. I believe that the relative degree of reliance upon these four cognitive elements determines one's temperament, as described in the study of personality typology stemming from C.G. Jung's work (Keirsey & Bates, 1984). The apparent wisdom of Nature in apportioning the four temperament types through the human population is striking:

Sensation/Judging (SJ) types (about 38% of us) are duty-bound traditionalists who need to be useful members of society. I see them as motivated almost exclusively by the lymbic system, creating left-brained, orderly rules and explanations to support their innate values. They build the secure, cohesive society from which the other types can pursue expansion.

Sensation/Perceiving (SP) types are action-oriented and impulsive, motivated by the thrill of intense experience and the need for freedom. My guess is that this temperament results from interplay among the left and right forebrain and a dominant somatosensory cortex. From this (approximately 38%) portion of humanity we get explorers, performers, hunters, pilots -- intrepid souls who will risk all in pursuit of excellence (the thrill of victory, the finest sensory pleasures) or variety (new experiences), and will fight to the last breath for freedom.

Some 12% of us are Intuitive/Feeling types questing after the meaning of life, becoming oneself, pursuing self- actualization. They are our idealists, and personify the conscience of society. Their approach to life is evaluative rather than analytical, their concern for spiritual excellence. I see this temperament as the right-brained conviction that our epigenetic social values (which they can hardly imagine as inherited or automatic lymbic mechanisms) must have a deeper meaning that expands beyond the social arena, imbuing all of life with intrinsic value.

The last 12% or so of humanity is composed of Intuitive/Thinking types. These are analytical seekers of truth, knowledge and understanding. Distrustful of inaccurate perception and conflicting emotions, they seek a rational experience of life, an accumulation of talents and abilities, and freedom from bias. Operationally, this appears to involve ignoring the lymbic and somatosensory systems except to satisfy basic needs, and indulging in an internal dialog between the frontal left and right hemispheres. From this emerges the scientific perspective, pursuing both excellence and variety of information about our universe and of our power to operate effectively within it.

While we mustn't overstate the case here -- temperaments in real live humans are influenced by all of these aspects, and the proportion of influence is quite changeable over time -- there is clearly in most of us a predominant tendency toward one of the four temperaments.

Particularly applicable to this discussion is the valence between an individual's temperament and his interest in science or philosophy. The analytical NT temperament is naturally attracted to science, and is driven to produce accurate, unbiased results; but the social implications of those results may never be considered. The evaluative NF temperament is attracted by the normative facet of philosophy, and will suffer any amount of anguish in the pursuit of what is good and right; yet there may be no connection between those laudable values and truth.

Our conscious experience of the reticular and lymbic guidance mechanism is self-image. Like a news reporter, self-image must answer the multiple question, "_____ am I?" filling in the blank with the essential adverbs: where, when, who, what, why and how. This report is updated continually during waking hours.

"Where" and "when" are questions of basic orientation; "where" is the most urgent upon awakening in unfamiliar surroundings, and is otherwise quietly unobtrusive; "when" is also an orientation question, important in dealing with deadlines or long-range planning.

"Who" is a question of basic identity, the answer to which emerges developmentally at about 18-24 months of age (Kagan & Segal, 1988, p. 513). "What" is also a question of identity, relating to personal appearance, traits, abilities and social position -- one's place in the world; this part of self-image is well-formed by adolescence, but continues to be modified through life. SJs are strongly concerned with their place in society, while the other three temperaments are more concerned with their individual attributes.

"Why" has two components: The situational interpretation involves awareness of the chain of causality (evolutionary process) that has led to the present moment, and is preferred by NT temperaments. The existential aspect questions the meaning of life, the purpose of existence in general, and is a quintessential NF temperamental function. SJ and SP types are not generally prone to wonder about this, and will usually follow the lead of NFs or NTs respectively.

"How" is the most important of these questions; it is an assessment of all basic needs, intermediate desires and idiosyncratic whims, of one's worth, potency and competence, and of the adequacy of the other components of self-image above; the answer determines the level of self-esteem.

Self-image is man's internal guidance system, and its most important component is self-esteem. Self-image determines which values one chooses -- the epigenetic personal and social values we're born with, values dictated by a social superior or by the culture at large, or values painstakingly reached through rational inquiry. Self-esteem determines whether we have the motivation or power to act on those values.