“The implications are, quite literally, mind-bending. At birth, the human brain weighs a mere 25 percent of its eventual adult weight. This is a curious state of affairs for the brainiest of the primates. A macaque, by contrast, is born with a brain that is 60 percent of its adult weight. Its neural growth has already slowed dramatically while still in utero. Even our closest primate relation, the chimpanzee, is born with about 45 percent of its brain weight already developed, and its brain growth slows down shortly after birth. Chimps mature both physically and socially years ahead of their human cousins.
Among primates, only the human brain continues to grow at fetal rates after birth, and the frantic pace of this postpartum neural building boom continues for the first two years of life before it begins to show any signs of abating. The cortex’s natural insulation, the fatty myelin sheath that grows about the axons and permits efficient conduction of electrical impulses, is not completely formed until about the sixth year of life. Only at puberty is the physical maturation of the human brain complete. After that, neural development continues throughout life. But this is, strictly speaking, more a matter of “mind” than of brain.
This delayed maturation of the human nervous system is paralleled by a general developmental retardation of the human child compared with other primates. Humans also show a tendency to both physiological and behavioral neoteny, retaining juvenile traits in adult forms of both anatomy (i.e., head-body ratio) and behavior (i.e., playfulness).
This combination of premature birth and retarded development means that fully three-quarters of the human brain develops outside the womb, in direct relationship with an external environment. Evolution has equipped our species with an “ecological brain,” dependent throughout its life on environmental input. This is a factor of extraordinary significance for cultural anthropology and cognitive psychology alike.
The human nervous system has presumably been preadapted by evolution for many perceptual skills. Take, for example, common human visual abilities like binocular vision, depth perception, back and forth translations between three-dimensional visual images and two-dimensional representations, mental rotation of imagery, or perceptual coordination of sight, sound, and touch. Though the human sensorium seems to be genetically prepared for such visual acrobatics, actual feats of perception must be brought to life through an individual’s concrete interactions with the world. People blind from birth that eventually gain vision through medical procedures can immediately “see” by means of their eyes but have to learn by practical experience to “perceive” actual forms and to coordinate perceptual relations between sight and other senses like touch.
The eco-logical brain does not develop simply in a natural environment. Our nervous system unfolds in relation to two quite different kinds of environment, the one more “natural” and the other more cultural. Basic cognitive skills like perception, classification, and inference have evolved in the species and develop in individuals as ways in which a particular kind of body (a human body) interacts with the contours of a particular kind of physical world.
Ecological psychology studies ways in which the human sensorium is pre- adapted to the “affordances” (i.e., the interactive possibilities and constraints) of such a generalized human life-space. Just as a toddler’s foot and leg muscles must learn to balance and carry an upright body over a complex and ever-changing terrain, so the human sensorium has learned to “read” its physical environment in the (evolution- ary) process of interacting with it.
At the same time, neural development also takes place within very particular and variable sociocultural environments. Cross-cultural psychologists have demon- strated that even basic aspects of perception are influenced by the way that experience is “modeled” by a particular sociocultural environment (Cole and Scribner, 1974). These “cultural models” might be usefully thought of as “cultural affordances,” equivalent to the physical affordances of the natural environment.
For example, individuals growing up in cultures lacking two-dimensional realis- tic art must learn how to recognize images when presented with photographs. Simi- larly, there is evidence that people raised in “carpentered environments” (with lots of measured, regular angles and straight lines) tend to be fooled by certain optical illu- sions in a way that is not generally true for those raised in visually “natural” environ- ments lacking artificial lines and angles and with no experience of two-dimensional representations. One cross-cultural psychologist who has studied cultural differences in numerous perceptual skills concluded that “ecological demands and cultural practices are significantly related to the development of perceptual skills. … In some sense, cultural and psychological development are congruent (Berry, 1967:228, quoted in Cole and Scribner, 1974:85).
So an important part of the evolutionary heritage of the sapient hominid is a nervous system that has evolved under the sway of culture (in general) and which develops in each individual under the sway of a culture (in particular). The human nervous system appears to be dependent on external models or programs for normal operation, and this notion of models has significant importance for anthropologists and psychologists alike.
from Culture in Mind: Cognition, Culture, and the Problem of Meaning by Bradd Shore.
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