Complexities: Beyond Nature and Nurture
296
Complexities: Beyond Nature and Nurture
296Paperback
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Overview
Complexities mobilizes experts from several fields of anthropology—cultural , archaeological, linguistic, and biological—to offer a compelling challenge to the resurgence of reductive theories of human biological and social life. This book presents evidence to contest such theories and to provide a multifaceted account of the complexity and variability of the human condition. Charting a course that moves beyond any simple opposition between nature and nurture, Complexities argues that a nonreductive perspective has important implications for how we understand and develop human potential.
Product Details
| ISBN-13: | 9780226500249 |
|---|---|
| Publisher: | University of Chicago Press |
| Publication date: | 06/01/2005 |
| Pages: | 296 |
| Product dimensions: | 6.00(w) x 9.00(h) x 0.80(d) |
About the Author
Sydel Silverman is president emerita of the Wenner-Gren Foundation for Anthropological Research and professor emerita of anthropology at the City University of New York.
Read an Excerpt
COMPLEXITIES
Beyond Nature & Nurture
THE UNIVERSITY OF CHICAGO PRESS
Copyright © 2005 The University of Chicago
All right reserved.
ISBN: 978-0-226-50024-9
Chapter One
Epigenesis, Brain Plasticity, and Behavioral Versatility: Alternatives to Standard Evolutionary Psychology Models
Kathleen R. Gibson
Creativity, versatility, and advanced learning capacities are primary hallmarks of the human mind. Our species inhabits six continents that encompass environments as diverse as the Arctic, the tropical rain forest, and the Australian outback. Individual humans routinely move between different climatic zones and cultures, and they readily adapt to the dramatic technological and social changes that now occur within individual life spans. Moreover, in less than ten thousand years, a mere blink of the eye in evolutionary terms, much of the human world has moved from a hunter-gatherer to a postindustrial lifestyle, all the while exhibiting such extraordinary reproductive success that our very numbers now threaten the planet.
These accomplishments reflect the ability of humans, working individually or in groups, to devise novel solutions to new environmental challenges and to transmit these solutions to others through social learning processes. This human behavioral versatility stands in contrast to prominent evolutionary psychology models that posit that the human brain is neither a generalized learning device nor a generalized problem-solving device. Rather, it is assumed to consist of numerous domain-specific, genetically determined neural processing modules designed to solve highly specific problems encountered during human evolution (Fodor 1983; Irons 1998) or, more specifically, during the Pleistocene hunter-gatherer environment of evolutionary adaptation (the EEA) (Barkow, Cosmides, and Tooby 1992). Cosmides and Tooby, for example, hypothesize that the human brain has numerous distinct mental modules related to social intelligence, including probable innate "cheater detector," "theory of mind" (the ability to infer others' intentions and thoughts), and "reciprocal altruism" modules (Cosmides and Tooby 1992; Tooby and Cosmides 1992). Similarly, Pinker (1994) and Chomsky (1972) inform us that our brains possess innate syntactic capacities that are unrelated to other cognitive and intellectual skills, that indeed there may be a specific language gene (cf. Foley, chapter 2, this volume).
Evolutionary psychology models have distinct strengths, especially the recognition that humans are biological beings whose behavioral capacities evolved under natural selection and are mediated by neurological, genetic, and other biological mechanisms. Standard evolutionary psychology models (SEPMs), however, ignore the well-established genetic and developmental principles of pleiotropy (individual genes have multiple phenotypic effects) and epigenesis (phenotypic traits reflect genetic and environmental interactions during development). Thus, they often inappropriately generalize from phenotype to genotype and are inherently flawed in the scientific sense. This chapter summarizes evidence that, rather than being a collection of highly specific, genetically determined mental modules, the human brain is a highly plastic organ that develops functional specialization over the course of a lifetime through interactions between environmental and genetic effects. It also examines evidence that the human brain was designed via natural selection to provide the mental flexibility and creativity needed to confront varied, often novel, environmental conditions. The functionally plastic nature of the human brain and its inherent creativity render suspect all arguments that complex behaviors are controlled by innate, highly localized, behaviorally specific neural modules.
The Highly Variable Environments of Evolutionary Adaptation
As summarized by Irons (1998), the concept of an environment of evolutionary adaptation was first proposed by the psychologist John Bowlby (1969, 1973), who considered the natural human environment to be the one inhabited by humans for the two million years prior to the last few thousand years-although he did not specify much about the nature of that environment. This concept is reiterated with minor modification in The Adapted Mind (Barkow, Cosmides, and Tooby 1992), whose contributors propose that the human mind is adapted to the Pleistocene hunter-gatherer environment occupied by humans for two million years prior to the invention of agriculture, again without specifying much about that environment. They claim that too little time has elapsed since the invention of agriculture for natural selection to have changed human behavioral adaptations.
This concept that our hunter-gatherer ancestors encountered relatively uniform challenges for two million years stands as a central tenet of the SEPMs, although not one that has gone unchallenged even in the evolutionary psychology community. Irons (1998), for instance, notes that during the approximately two-million-year period prior to the emergence of agriculture, several new hominid species evolved. This suggests considerable behavioral and genetic change during this time frame. In the last few thousand years, as Irons notes, humans in some populations have also evolved adaptations to milk drinking and to malaria that are not present in all human populations. This indicates that contrary to SEPMs, sufficient time has elapsed since the invention of agriculture for new genetic adaptations to have arisen.
Moreover, there is no single hunter-gatherer environment and probably never has been. Modern hunter-gatherers encounter diverse environmental challenges with respect to climate, terrain, and resource availability. True, all hunter-gatherers must have means of predicting the time and place of food availability, of traveling to and from foraging sites, of procuring, processing, and transporting foods, of finding mates, of rearing children, and of protecting themselves from environmental hazards. Although all modern hunter-gatherers must meet these common challenges, they do so by highly varied means. Depending on the population and the season, hunter-gatherer staple foods may include nuts, tubers, beans, fruits, fish, sea lions, fowl, shellfish, ungulates, rodents, kangaroos, or invertebrate prey-a diversity of foods that require a diversity of foraging and processing techniques. Populations that forage on similar foods may also use very different techniques. Animal prey, for instance, can be driven over cliffs or into corrals, cornered in mountain passes, stalked by individuals armed with spears, bows, bolas, or boomerangs, ensnared in traps or lured with bait and mating calls. Diverse hunting strategies demand varied forms of social interaction and social sharing. Similarly, travel and protection from climatic, predator, and other environmental hazards demand different strategies depending on location.
Comparative behavioral evidence and paleontological data suggest that versatile human behavior patterns have a long evolutionary history. Our closest phylogenetic relatives, the chimpanzees, display population variations in foraging, tool-using, and communicative techniques that indicate a capacity to invent and socially disseminate novel behaviors (Boesch 2000; McGrew 1992; McGrew et al. 2001; Russon 2000; Whiten et al. 1999; Wrangham et al. 1994). Some chimpanzee populations, for example, use sticks to "fish" for termites. That is, they insert sticks into openings in termite mounds and allow termites to crawl up the sticks. Others use sticks to dig into the termite mound. Similarly, some chimpanzee populations use tools to crack nuts; others simply choose not to eat the same nuts, even when they are present in their environment. Population variations in social behavior also exist. For example, chimpanzees in the Mahale Mountains, when grooming each other, extend their nongrooming hands above their heads and clasp them (McGrew et al. 2001). Chimpanzees at the Gombe Stream do not exhibit this behavioral pattern. Chimpanzees and other great apes also manifest a certain amount of developmental plasticity, as is evident from the behaviors of apes reared by humans. Human-reared apes, for instance, may comprehend much spoken English and communicate symbolically using gestures similar to those used in the American Sign Language of the deaf or by using visual pictograms. Those reared in the wild fail to master these skills even after being captured and trained (Savage-Rumbaugh et al. 1993). Human-reared apes also appear to exceed apes reared in the wild in their imitative and mirror self-recognition capacities (Parker, Mitchell, and Boccia 1994). Comparable levels of developmental plasticity, creativity, and social learning skills would have been present in the last common ancestors of chimpanzees and humans.
It was once thought that hominids evolved in a savanna habitat and that some hominid characteristics, such as bipedalism and tool use, were specific adaptations to savanna life. We now know, however, that forest-living chimpanzees use tools (Boesch 1993). The fossil record also indicates that the earliest hominids, in the period from about 2 to 4 million years ago, rather than living in the savanna, lived in highly "mosaic" environments containing wet woodlands and lakeside environments as well as more open habitats (Potts 1996, 1998). These hominids were already bipedal, but they also retained tree-climbing adaptations. Thus, they appear to have exploited both arboreal and terrestrial habitats. By about 2.4 million years ago, savanna habitats were expanding, and by about 1.8 million years ago, fully bipedal hominids had appeared. During this period, however, and throughout the subsequent Pleistocene, evidence indicates that mean global temperatures and sea levels fluctuated frequently, leading to periodic changes in terrestrial climates. For example, at one fossil site, Olduvai Gorge, the habitat was at times a relatively moist, humid, lakeside environment and at other times dry and semiarid. These climatic fluctuations resulted in repeated, major changes in the fauna and flora available for human consumption and, thus, favored the survival of versatile hominids capable of exploiting generalist behavioral strategies (Potts 1996, 1998). Selection would also have favored hominids capable of devising novel solutions to novel problems and of transmitting successful solutions to kin or mates.
Indeed, paleontological evidence indicates that by 2.5 million years ago hominids had responded to these environmental conditions by expanding their diets to incorporate foods not found in the diets of great apes-including the meat of big game, bone marrow, and, possibly, deeply buried tubers (Blumenschine and Cavallo 1992; Foley 1995 -96; Potts 1998; Tattersall and Schwarz 2000). Archaeological evidence also indicates that by 2.5 million years ago hominids may have been caching tools and foods at specific sites for future use-a new behavioral pattern not found among the apes (Potts 1998). By 1.8 million years ago, or about the time evolutionary psychologists assume our ancestors had adopted the EEA, behavioral versatility had allowed hominids to leave Africa and to occupy distinctly non-apelike environments in Asia and Georgia (Tattersall and Schwarz 2000).
Hence, even prior to the emergence of our species, hominid predecessors had demonstrated a behavioral versatility that enabled them to survive in a diversity of climatic and geographical conditions. This suggests that natural selection favored those hominids with the neural and mental capacities to solve novel problems rather than those able to solve only those problems encountered by their ancestors.
By the time of the emergence of anatomically modern humans, the evidence for behavioral flexibility and creativity in response to varying environmental challenges is incontrovertible. Even prior to the development of the European Upper Paleolithic, human populations in the Levant evidenced seasonal migration cycles possibly as complex as those exploited by any modern human group (Lieberman and Shea 1994). Evidently, they had learned to exploit seasonal feeding "bonanzas," such as seasonal crops and seasonally migrating animal prey (Gibson 1996a). Europeans began hunting large herd animals and learned to predict and exploit the seasonal migrations of herds of caribou and the seasonal spawning of salmon (Mellars 1973; Stiner 1994); populations in South Africa timed seasonal migrations to coincide with the beaching of sea lions (Klein 1989); East African populations developed complex fishing gear (Brooks et al. 1995; Yellen et al. 1995); and other groups reached Australia, where they flourished in environments whose fauna and flora bore little resemblance to anything previously encountered by hominids (Roberts, Jones, and Smith 1990).
In sum, at no period of human evolution did our ancestors exploit a single EEA. The geographical distances and evolutionary time frames are sufficient that given genetic or reproductive isolation, individual populations might have evolved dedicated neural processing modules to meet the specific needs of their own environments (Irons 1998). That this did not happen, however, is evident from the ability of peoples from all parts of the world to interbreed and to readily adopt each other's cultural practices, as well as from the abilities of peoples throughout the world to adapt to the modern postindustrial world. The behavioral and paleontological evidence, thus, suggests that the human brain has been designed for behavioral versatility rather than for the solving of a relatively few frequently encountered ancestral problems.
Epigenesis and Neural Plasticity: Partial Foundations of Human Versatility
The SEPMs assume that many identified mental or linguistic capacities of modern human adults reflect the functioning of domain-specific neural modules (i.e., functionally encapsulated areas of the brain), that these modules are innate, and that they evolved subject to specific selective pressures. Genetic and developmental evidence, however, sheds doubt on these assumptions.
Most genes influencing complex traits have multiple phenotypic effects (pleiotropy). This well-established principle should caution all behavioral scientists against assuming that each identifiable human behavioral capacity is controlled by a specific, dedicated gene. Indeed, it mandates a search for genes with multiple effects. A further mandate for such searches derives from our current knowledge that humans possess approximately 30,000 genes and that humans and chimpanzees differ in only 1.6 percent of their DNA (Paabo 2001). This minimal genetic difference must account for all of the genetically based physical and behavioral differences between humans and chimpanzees.
In fact, a gene has now been identified that is sometimes referred to as a language gene (Lai et al. 2001). Predictably, it follows the principle of pleiotropy in that a mutated form of this gene has multiple effects involving syntax, dysarthria, facial dyspraxia, and IQ. That any theory postulating individual genetic control of multiple small neuronal populations must be faulty is also evident from the fact that although there are approximately 30,000 human genes, there are 1 trillion neurons and between 100 and 1000 trillion synapses (Ehrlich 2000). What is needed is not a theory that one gene = one mental module = one complex behavior but a theory of how a small number of genes can construct a complex brain and enable a diversity of behaviors.
Anatomical and functional studies of normal and diseased human brains, however, often appear to lend support to concepts of multiple, domain-specific neural modules. All normal human brains, for instance, contain dedicated sensory and motor processing areas that are predictably located in the same neuroanatomical areas in most people. In some species, species-typical facial, spatial, and object recognition cortical areas have also been identified (Haxby et al. 1996; Movshon et al. 1985; Tanaka 1996). Broca's and Wernicke's areas of the left human neocortex have long been thought to be dedicated linguistic processors, and some scholars have postulated that separate cortical areas mediate recognition of differing word classes such as those for animate versus inanimate objects (Grabowski and Damasio 2000).
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Table of Contents
PrefaceIntroduction
Susan McKinnon and Sydel Silverman
I. Challenging Reductive Theories of Mind
1. Epigenesis, Brain Plasticity, and Behavioral Versatility: Alternatives to Standard Evolutionary Psychology Models
Kathleen R. Gibson
2. Do Humans Have Innate Mental Structures? Some Arguments from Linguistics
William A. Foley
3. The Eye of the Beholder: How Linguistic Categorization Affects "Natural" Experience
Eve Danziger
II. The Limits of Universal Models
4. Reassessing Male Aggression and Dominance: The Evidence from Primatology
Katherine C. MacKinnon and Agustin Fuentes
5. On Kinship and Marriage: A Critique of the Genetic and Gender Calculus of Evolutionary Psychology
Susan McKinnon
6. Surveying a Cultural "Waistland": Some Biological Poetics and Politics of the Female Body
Mary Orgel, Jacqueline Urla, and Alan Swedlund
7. Denaturalizing Gender in Prehistory
Lynn Meskell
III. Putting Genes in Context
8. Context and Complexity in Human Biological Research
Thomas Leatherman and Alan Goodman
9. Alzheimer's Disease: A Tangled Concept
Margaret Lock
10. The Molecular Revolution in Medicine: Promise, Reality, and Social Organization
Karen-Sue Taussig
IV. The Politics of Reductionism
11. Barbarism, Old and New: Denaturalizing the Rhetoric of Warfare
Mary H. Moran
12. Language Standardization and the Complexities of Communicative Practice
John J. Gumperz and Jenny Cook-Gomperz
13. Blood and Belonging: Long-Distance Nationalism and the World Beyond
Nina Glick Schiller
List of Contributors
Index