Teleodynamics

INTRODUCTION

Neuropsychological theories make implicit assumptions about brain organization and the relationships between structure and function. These include assumptions about the movement and representation of information within brain structures and neural circuits and about the phylogenesis and development of these substrates. Unfortunately, our knowledge of human neuroanatomy remains incomplete and is particularly lacking in detailed information about the patterns of axonal connections-the basic circuits of the brain. As a result, the anatomical assumptions of neuropsychological theories are often represented by no more than diagrams of logical relationships between operationally defined functions, where the relationships are attributed to connections and the functions are assigned to areas.

The last decades have seen remarkable advances in experimental neuroanatomy using nonhuman species. Since the discovery of autoradiographic and peroxidase axonal tracer techniques in the 1970s, the development of information concerning the connectional patterns of monkey, cat, and rat brains has proceeded at an explosive rate. It is probably not too ambitious to expect that the details of the connectional anatomy for the brains of these model laboratory species will be thoroughly catalogued well before the turn of the next century. Although we still lack the means to directly analyze human brain circuitry at a comparable level of detail, the remarkable similarity in cellular and connectional anatomy in mammalian brains makes it possible to apply many of these general findings to the problem of understanding human brain anatomy.

If the 19th century “diagram makers” were guilty of inventing, singling out, or oversimplifying neural connections to fit their psychological models of brain processes; neuropsychological theories at present are guilty of ignoring the growing body of “diagrams” of empirically identified neural connections. Maps of the direct and indirect pathways through which information can be transmitted within the brain, and of the general patterns these pathways exhibit, can provide rigorous constraints within which to guide development of models of brain function. Perhaps for the first time in the study of the human brain it is possible to ask what sort of neuropsychological theories are suggested by the anatomy rather than the other way around.
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Terrence W. Deacon
Biological Anthropology
Boston University, Boston, MA 02215

From A. Scheibel & Wm. Schopf, eds. (1997) “The Origin and Evolution of Intelligence,” Jones and Bartlett publishers, pp. 103-135. Revised post-publication April 2000 (originally written in 1995-6).

The persistence of top-down explanations in biology
When the theory of natural selection was first presented to the scholars of the last century, many found it to be too implausible to believe. The incredulity of many great thinkers at the time, from brilliant biologists to articulate theologians, was based on a well-reasoned common sense understanding of the world: Left to chance, things tend to get less organized, not more. Millennia prior to Darwin, this same reasoning led Aristotle to criticize the natural philosophy of his contemporary, Empedocles, who argued that all natural processes are the actions of blind chance and that organisms arise out of the preservation of useful accidents (see Aristotle’s Physics). Aristotle easily found innumerable examples of end-directed design in nature that he felt could on no account be explained from such a minimalist perspective. But Aristotle was wrong about this, and only after more than twenty centuries of musing about this conundrum, did scientists come to realize the power of the opposed conception for explaining biological phenomena. When the logic behind Empedocles’ insight was rediscovered and given a more substantive interpretation by Darwin and Wallace, it revolutionized biology by providing an answer to this counterintuitive problem. This has become widely appreciated, not just by biologists, but by the general lay public educated in basic biology.

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One of the great mysteries of animal development is how the cells in mouse embryos and elephant embryos know how many times to divide before committing to fixed cell fates in each tissue in order to produce proportioned adult bodies of vastly differing sizes. Given the incredible difference in scale from zygote to adult organism, it is remarkable that many comparative morphological relationships exhibit highly predictable scaling patterns in animals of different sizes. Such regularities imply that the control of differentiation and growth is highly conserved and tightly regulated even when extrapolated in time and space over many orders of magnitude. Not surprisingly, elephants take longer to grow than do mice, and they also take longer to reach developmental stages comparable to those of mice. Surprisingly, the two animals reach these different end points from highly similar beginnings and by using almost identical mechanisms extrapolated to different degrees during development. Thus, the timing mechanisms underlying development play critical roles in animal design, and their variations are widely cited as likely major factors in morphological evolution. Time, growth, and developmental differentiation of tissues are linked variables, but the mechanisms linking them, the extent to which each is dissociable from the others, and the role these relationships play in the evolution of animal forms remain poorly understood.

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