Perspectives On Medical Research
Volume 5, 1995
Aping Science
A Critical Analysis of Research at the Yerkes
Regional Primate Research Center
A. Behavioral Studies
Yerkes' researchers have asserted that their monkey and ape behavior studies
serve the public interest by providing "models" of aberrant human
behaviors, such as drug addiction. They have claimed this research has offered
insight into normal and abnormal human mental development and has elucidated
the "biological roots," or "evolutionary origins," of various
human behaviors.
1. Primate Cooperation and Aggression
The Yerkes 1989-1990 Annual Report has claimed:
Chimpanzees at the Yerkes Field Station were studied by Dr. Frans de Waal ...to examine whether food sharing is the propelling force in human evolution, particularly in the development of systems of mutual social obligation. . . . Such research improves our understanding of the possible roots of human social interaction--how our human ancestors learned to cooperate and live together for mutual benefit.1
By studying the behavior of different species of monkeys and apes at the Wisconsin Regional Primate Research Center and the Yerkes field station, Frans de Waal has claimed to have gained insights into the biological basis of cooperative behavior in human beings. He has published extensively in the public and scientific literature,2,3 and his books include the well-known Peacemaking Among Primates.4 A typical finding is that chimpanzees living in outdoor enclosures who shared food are more likely to receive favors from others and less likely to encounter aggression.5,6 From that observation, de Waal has concluded, "We can incite the need for peace and increase reconciliation by increasing need for each other--that's a clear message of primate research, I think."7 After studying reciprocity in chimpanzees, de Waal has summarized, "Some of the mechanisms relate to human systems of morality and justice in that they appear to serve retribution and the enforcement of reciprocity rules."5 Working with monkeys, de Waal found that, contrary to expectation, rhesus monkeys living together in close quarters were more cooperative than those living in less confined conditions.8
While De Waal's research may apply to certain populations of captive monkeys and apes, it is not reasonable to extrapolate the findings to wild nonhuman primates, much less to humans. De Waal's claim to have clarified the biological basis of human "reciprocity" as evolving from food-sharing is unsound on at least two counts: 1) human behavior is not genetically determined, but arises from a complex interaction between environment and heredity, and 2) chimpanzees are not simply primitive humans. Chimpanzees and humans are distinct species that have evolved separately over 5-10 million years to meet different environmental challenges. Anthropologist Milford Wolpoff has noted that present-day chimpanzee behavior may differ markedly from ancestral chimpanzee behavior 4-6 million years ago.9
De Waal and other primatologists rarely claim explicitly that their findings directly apply to humans. However, by using terms like "cooperation" and "retaliation" they imply that the absented nonhuman primate behavior closely resembles well-understood human social behaviors. No doubt, like humans, nonhuman primates have complex social relationships that have analogues in humans. But, the meaning of specific social behaviors for them may well differ considerably from the meaning of similar behaviors for humans, just as a given human behavior cannot be well-understood outside of its social or cultural context. For example, "human aggression" depends on its context. Aggressive actions during times of war differ markedly in motives and manifestations from aggressive driving or aggressive activities aimed at professional advancement. When dealing with nonhuman animals who cannot verbalize their motives, it is not possible to know whether inferences about the meaning of their activities are valid. Even in the study of humans, who can verbalize their motives, the meaning of behavior is often unclear.
De Waal's observations have nevertheless captured the attention of the
scientific community and the public because nonhuman primates are extraordinarily
powerful metaphors of humans. Their physical appearance and their behaviors
are strikingly "human." No doubt, all primates share similar
basic emotions, such as fear, anger, and happiness. However, there is
no reason to expect that, in their nuances, their behaviors are closely
analogous. The effects of culture, individual personality, and thinking
influence behavior in all primates. The dramatic impact of such
primate studies should not be confused with their dubious scientific
content. Consequently, it would be folly to theorize human psychology
in terms of observed nonhuman primate behavior.
2. Culture in Great Apes
The Yerkes' Annual Report has contended:
Dr. Michael Tomasello ... found very little inter-individual consistency or intraindividual stability in gestures four years after the young animals' gestures were first documented. The research countered the notion that each chimpanzee group possesses a single repertoire of gestural signals that is passed along from one generation to the next arid that each individual in the group learns to communicate primarily by imitating others.1
Tomasello has found that chimpanzees raised at Yerkes do not transmit gestures acquired in adulthood to offspring. He has attempted to extrapolate this finding to both wild chimpanzees and human beings. In the 1992 Annual Progress Report to the NIH National Center for Research Resources, Tomasello has written:
Results show that chimpanzees do not culturally transmit gestures across generations. The implication suggests that humans have special abilities to learn and use communicative symbols, and the processes by which they do so may be specified so as to have implications for children who have difficulty learning language.10
However, field investigators have shown that wild chimpanzees often do transmit behaviors regarding food preferences, tool making and use, and gestural dialects to their offspring.11 Captive chimpanzees might not display these behaviors because of the intellectually deprived and socially restricted environment in which they have been raised. The unnatural conditions in the laboratory make conclusions difficult.
Tomasello has also proposed that the human ability to learn and use communicative symbols is genetically based, but absent in chimpanzees' genetic material. Furthermore, Tomasello has claimed, human children who have difficulty learning behavior and language might, like chimpanzees, lack this genetic material.12 There is no factual basis for so wild an hypothesis, which represents an unwarranted application of captive chimpanzee data--which may not even apply to wild chimpanzees--to humans. It is biologically naive to propose that learning disabled children share some sort of inherent genetic deficiency with chimpanzees. Tomasello, like many researchers investigating nonhuman behavior, has confused ontogeny (development of an individual) with phylogeny (the evolution of an entire group, e.g., species).13 No doubt, ontogeny reflects phylogeny, but culture and individual attributes contribute to each individual's unique character.14-16 However, nonhuman primate researchers assume that nonhuman primates are like proto-humans--organisms that effectively stopped evolving. According to this notion, it should be possible to determine the origins of human social activities by studying their "primitive" attributes in nonhuman primates. Of course, other primates did not stop evolving millions of years ago, but rather evolved physical and social attributes to serve their own survival needs in their own environments. Their behaviors after millions of years of continued evolution may vary considerably from those ofhumans.
If Tomasello and co-workers can learn anything in their laboratory setting,
it pertains to the particular types of primates under specific laboratory
conditions. No doubt, analogies exist among primate species, but learning
is a cultural phenomenon, and each species' learning reflects its own,
unique interplay between genetic and environmental influences.
3. Mental Competence in Great Apes
Yerkes officials have maintained:
An augmented language learning approach that helps children with severe mental retardation has been developed from the Yerkes Center's behavioral studies with chimpanzees. The components of the language learning approach are: a vocabulary of visual graphic symbols, each representing a word; a computer-operated language board of keys, each embossed with a symbol; and teaching strategies that break language learning into small discrete steps and emphasize the functional use of symbols.1
Duane Rumbaugh and colleagues have also contended that their studies of chimpanzee learning with computerized language learning and communication boards can be applied to teaching mentally retarded children.17,18 Rumbaugh is best known for teaching chimpanzees to count and form rudimentary sentences with a computerized board.17,18 Studying chimpanzees in a low-stress, semi-natural environment, Rumbaugh and colleagues have demonstrated certain chimpanzee mental skills. Such findings can help us understand chimpanzees, and it may encourage people to treat them with more respect. For example, they have taught a bonobo chimpanzee named Kanzi to use several hundred words, illustrating that remarkable linguistic skills are possible in members of other species.19 However, as Lewontin argues,20 this research cannot shed light on abnormal human language acquisition or the evolutionary origins of human language. Rumbaugh has claimed relevance to humans on the grounds that "humans are primates,"17 and, like Tomasello and others, he confuses ontogeny with phylogeny. Language is culturally acquired, and its origins cannot be revealed from studies of "closely related" species.
While Rumbaugh has also contended that his chimpanzee studies were necessary to develop computerized learning boards for mentally retarded children, the primary function of Rumbaugh's chimpanzee studies has been simply to "dramatize" the potential of computerized learning boards. This may have encouraged some researchers and teachers to try using them with mentally retarded humans. Such a rhetorical function, while perhaps important sociologically, is not important scientifically. Indeed, educational programs for mentally retarded children have been based on observational and other clinical studies of these children. Human clinical research at Emory University and elsewhere have provided details on which learning apparatuses are most helpful for mentally retarded individuals.21,22
Rumbaugh and colleagues have also studied rhesus monkey performance using a "joy-stick" to shoot at targets on a video screen. For example, they have reported that, contrary to others' findings, rhesus monkeys could manipulate an object from afar (9 to 18 centimeters).23 Also, they found that monkeys, when competing with each other for food rewards, hit the targets much more quickly than in uncontested conditions.24 They have concluded, "A competitive video task produced robust, reliable and, we think, meaningful effects on the monkeys' performance."24 What is meaningful here? They have suggested, "Winning a competitive trial may have intrinsic value to the monkeys in addition to the reward received, as seems to be the case with humans."24 Nowhere do they propose new hypotheses for human competitive behavior, nor can their monkey research explain how or why humans often choose to compete with each other. In fact, they are not even certain the monkeys are really competing in the sense we understand it: "There is no evidence in these experiments to indicate whether either monkey knew that when it lost, the other won. Additional investigation may be addressed to resolve this issue."24 Of course, no experiment can determine whether or not a monkey knows that the other has won. While behavioral experiments may infer an animals' recognition of its environment, verbal communication is needed to assess its actual mental state.
While Rumbaugh's chimpanzee language research can provide interesting
information regarding chimpanzees, his laboratory's behavioral research,
such as the competition study mentioned above, is of very questionable
relevance to humans. Because each species' behavior reflects physiological,
psychological, and social attributes unique to that species, it is unwarranted
to translate observations about the behavior of one species to another.
Furthermore, without the necessary communicative tools, behavioral research
on nonhumans only provides superficial descriptive information, which
does not illuminate the animals' mental states. Therefore, such research
is not helpful in understanding other animals, much less human beings.
4. Primate Vocal Communication
Henry and Sarah Gouzoules have analyzed the role of screams among pigtail macaques
to recruit allies during conflicts.25,26 Regarding such research,
Yerkes officials have asserted:
Recent studies have challenged the notion that vocalizations of monkeys and apes are mere reflections of a caller's emotional state. Research on the vocal communication of monkeys living in social groups have revealed rudimentary, but intriguing similarities between certain aspects of human language and the vocalizations of these primates. Several species of primates have been found to use calls in ways that effectively represent objects or events in their external environment.1
Gouzoules and Gouzoules have found that certain kinds of screams were more likely to attract family members or other pigtail macaques to their aid. Neither of these reports draw any connection between their monkey findings and human means of communication.
Yet, Gouzoules and Gouzoules have contended that their research may illuminate the origins and acquisition of human language:
The overall goal of the program is to understand the function and ontogeny of nonhuman primate vocal communication in complex social contexts. The long-term aim is to explore cognitive dimensions of primate behavior that ultimately may provide insights into the evolutionary origins of human language. These studies will also contribute to a better understanding of the criteria for appropriate primate models for studies of language acquisition.22
Again, the ontogeny of individual monkeys is confused with the phylogeny of all primate species, including humans, and the researchers commit the typical error of behavioral pnmatologists. It is unrealistic to believe that nonhuman primate research can elucidate the "evolutionary origins of human language." Human language is not simply monkey communication plus several new skills. Human and nonhuman primate communication skills have evolved independently for millions of years to meet the needs of the respective species, and, in doing so, have developed different neurological bases. Although communication patterns in the two species may be similar through analogy or homology, the assumption that they are sufficiently similar so as to use one as a model for the other is unfounded.
Indeed, in many respects monkey vocalization and human speech are not comparable,
and studying one will not elucidate important information about the other,28 despite
numerous attempts to do so by other primate researchers using complex
and invasive procedures.29,30 Monkey and human vocalization
are quite different neuroanatomically, neurophysiologically, and neuropyschologically:
human vocalizations are generally produced voluntarily and controlled
with great ease, whereas monkey vocalizations seem largely dependent
on the arousal of strong feeling relating to some basic need;31,32 the
monkey brain area primarily involved in vocalization (peri-aquiaductal
gray) may not play such an important role as in human speech;29,33 and
the cortical areas34 and projections29 of nerve
impulses that mediate nonhuman primate cries and human speech differ.
Furthermore, in the wild, rhesus monkeys produce at least 20 different
calls, yet researchers have experimentally conditioned rhesus monkeys
to vocalize only a few such sounds,28 presumably reflecting
the importance of environment in monkey vocalization.
5. Social Change and Stress
Yerkes officials have declared:
Studies conducted with rhesus monkeys at the Yerkes Center are adding to the growing body of evidence that stress does affect the immune and hormone systems, and that the presence of a comforting companion can moderate stress.35
Deborah Gust and colleagues have done numerous experiments to assess physiologic alterations associated with changing the social environments of rhesus monkeys. They have focussed on behavior and "immunological parameters," particularly levels of cortisol and T-helper and T-suppressor lymphocytes. They have noted, "Numerous studies on rodents, monkeys, and humans have furnished evidence indicating that psychosocial stressors can influence the pituitary-adrenocortical and immune systems."36 Their diverse studies in rhesus monkeys have merely accorded with voluminous human and nonhuman studies. A brief description of recent experiments illustrates the nearly infinite possibilities afforded by this research paradigm, as researchers can vary duration of separation, age of separation, social environments before, during, and after removal of monkeys from a group, and numerous other factors:
1) Eight adult female rhesus monkeys who had been raised in large social groups were placed together. Prior to this experiment, some had been living indoors in individual cages and others had remained in social groups. The principle finding was that "social group formation is a potent psychosocial stressor in primates."36 Gust and colleagues have called for further research, looking at myriad possible parameters: "Further work in this area should include a control group and concentrate on behavioral correlates of stress-induced cortisol increases, functional changes that may occur in subsets of immune cells, and the role of previous housing and social conditions on the response of individuals to new group formation."~
2) Gust and colleagues removed juvenile rhesus monkeys from their social groups, which included their mothers and siblings. While there has been extensive research on infant separation, they noted that there has been "less attention to other age groups."37 They found, as one would expect, "These data ... fail to demonstrate a modulating effect of randomly chosen peer-mates on the stress effects produced by social isolation."37 Their protocol was analogous to removing a young child from his/her family, which is obviously psychologically traumatic for humans. If the monkey data had indicated otherwise, it would have been rightly ignored by those interested in human psychology and its physiologic correlates. Gust and colleagues have, predictably, called. for further research looking at other parameters: "To address the issue of increased susceptibility to disease following a social stressor, future studies should employ in vivo antigen challenges in addition to more widely used measures of immune competence."36
3) In a similar experiment, Thomas Gordon, Gust, and other investigators removed juvenile rhesus monkeys from their natal social group to indoor individual caging and returned the monkeys to their group several months later.38 As expected, all showed profound changes in cortisol and lymphocyte levels upon removal from their social environments, but return to the group had variable behavioral and immunological effects. The investigators have hypothesized that "the return, due to its social nature, was a unique experience for each subject."38 As in humans, in monkeys profound social loss causes stress; the effects of later social encounters depends on individual factors.
4) Gust and co-workers removed male adult rhesus monkeys from a large social group to all-male housing, and then returned them to the same social group one year later.39 They concluded, "Further research is needed to determine if sex, age, and/or previous experience with a stressor contributed to this lack of [initial] response [to removal from the group]. The return portion of this study, on the other hand, did support previous studies ... [and] adds to a growing literature demonstrating that behavior correlates with stress-related changes in physiology."39
5) Gust and colleagues removed adult female rhesus monkeys from a large social group and then either housed them alone or with a preferred companion from that group. They found that monkeys in the latter group had a faster recovery of cortisol and lymphocyte levels to baseline levels. These experiments were needed, they claimed, because "social relationships among humans are difficult to measure functionally."40 However, this highly artificial experimental design has questionable relevance to wild rhesus monkeys, much less to human beings. Nevertheless, the researchers have argued, "The area of social modulation of stress and the importance of the social bond is, indeed, interesting and complex and warrants further investigation."40
These experiments, and the numerous projects they are likely to spawn, appear to be intellectually vacuous. These researchers have merely quantified in monkeys the well-known fact that highly social animals (including all primates) are stressed by sudden, inexplicable removal from social contacts. Although it would be illegal to perform similar "controlled" experiments on humans, these artificial laboratory protocols have little parallel to human experiences. Furthermore, certain types of human social change, such as loss of a family member, can be, and have been, studied. Human studies offer the decided advantage that subjective factors associated with various kinds of stress can be verbalized, greatly assisting understanding of effects of stress on humans.
Gust's "social interaction" studies merely demonstrate in
monkeys already known human psychophysiological reactions. Social scientists
have long recognized that psychological, social, endocrinological, neurological,
and immunological factors all play a role in human stress responses and
diseases induction. Almost half a century ago, psychoanalyst Fritz Alexander
expounded on the concept of psychosomatic illness.4' In the 1950s, the
relationship between behavior and the hypothalamus-pituitary-adrenal
axis was appreciated.42 This was followed by clinical psychiatrist
Arthur Mirsky's criticism of reductionistic thinking when considering
disease processes. He emphasized the necessity of studying diseases processes
at different levels of organization by using different biological frames
of references--from the subcellular perspective to the holistic perspective--a
discipline he called behavioral medicine.43 This approach resulted in
the identification of multi-leveled etiologic mechanisms for the immunologically
based "psychosomatic" disease of asthma.44 Psychiatrist
George Engel then designated this multi-dimensional approach to understanding
a "mind-body" illness as biopsychosocial.45 Almost
30 years ago, the effects of separation stress in humans were appreciated
by noting the immuno-suppression and premature death from cancer and
infection found in surviving spouses.~ Accordingly, about 20 years ago
the field of psychoneuroimmunology was born from the study of humans.47
6. Drug Addiction
Yerkes officials have maintained:
Yerkes studies with monkeys by Dr. Larry Byrd ... and his colleagues demonstrated that behaviorally-active doses of cocaine and other psychoactive drugs can dramatically increase heart rate, blood pressure, and body temperature to unsafe and indeed deadly levels.
While the research of Dr. Byrd and others provided the medical-scientific community with evidence of the dangers of cocaine, the tragic cocaine-related deaths of University of Maryland basketball star Len Bias and other well-known individuals focused media and public attention on the hazards of the drug.
Current studies at Yerkes with monkeys focus on agents that can help humans recover from cocaine addiction or that might prevent cocaine addiction. The identification of antagonists of cocaine and other abused drugs will improve scientific knowledge about the behavioral and physiological effects of substances having stimulant properties and the factors that may explain the abuse of this drug in the human population.1
From 1970 through to date, Larry Byrd and co-workers' nonhuman primate addiction experiments have focused on: 1) the effects of addictive drugs on the social behavior of groups of monkeys, 2) addictive drug effects on physiology and behavior of monkeys and apes, 3) the effects of cocaine on monkey fetuses, 4) the physiological mechanism(s) by which cocaine addicts monkeys, and 5) strategies to prevent addiction in monkeys.48-59 These projects have elicited conclusions that are highly questionable in their applicability to clinical practice.
In the 1970s, Byrd and colleagues observed the effects of d-amphetamine on stumptail macaques' social interactions, concluding that "the observation of nonhuman primates living in a group under seminatural conditions can represent a powerful paradigm for studying,the behavioral effects of drugs."52 They found that social behavior of addicted monkeys reflects their social or dominance position. While it is likely that human drug abuse is influenced by social factors as well, it is unwarranted to apply the monkey observations to the human setting. There is no reason to expect that the meaning to monkeys of social position corresponds to meaning to humans of their particular place in society. And, because of communication difficulties, it is impossible to know.
The Yerkes group has written that the effects of social variables on monkey drug abuse "could not easily be studied in individual subjects removed from the group environment, and therefore these results lend credence to the value and importance of studying the behavioral effects of drugs under conditions that more closely approximate those of the human populations."52 But, the addition of social factors to the monkey drug abuse experimental situation does not make the research relevant to human drug abuse. Studying human social factors may be necessary, but monkey drug behavior in the laboratory does not even remotely resemble the "conditions . . of the human population." The entire paradigm of using monkey social behavior to model human social behavior is unsound. In contrast, clinical investigators, such as "street ethnographers," have studied how addictive drugs affect human social behavior by observing addicts in "crack houses" and elsewhere.60
Yerkes experiments on cocaine's effects on squirrel monkey blood pressure, heart rate, and body temperature48 have merely dramatized dangers long observed in human addicts. Indeed, the researchers themselves wrote that their findings "are consistent with published observations of the effects of cocaine in humans,"48 as if monkey data are required to corroborate human data. Likewise, their observations of rhesus monkey fetuses born to female monkeys who had been subjected to chronic cocaine administration have not led to discoveries relevant to humans. At best, their observations have accorded with clinical research findings of babies exposed to cocaine in utero.61 Nevertheless, Byrd and colleagues have defended their cocaine research on the following grounds:
few studies have examined the consequences of cocaine use during pregnancy under highly controlled laboratory conditions.... This project is studying in rhesus monkeys the effects of cocaine administration during gestation to characterize effects on the pregnant female, the developing fetus and the resulting offspring.62
However, it is impossible to reproduce human cocaine abuse in the laboratory--nonhuman primate or human--because drug use reflects psychological factors that change from day to day as well as other factors that do not have laboratory correlates, such as drug costs, drug purity, drug availability, drug mixtures, the setting, users' physical health, and others.63 Furthermore, differences between humans and rhesus monkeys in intrauterine environment, sensitivity periods, and rates of growth are among the many physiologic factors that undermine extrapolating from one species to another.
For these reasons, the modelling of researchers such as Byrd is invalid, despite their contention that the laboratory offers a "controlled" environment, where one variable can be manipulated at a time. When applying animal-model data to humans, this control becomes an illusion, because the researchers cannot control for fundamental inherent interspecies differences and they cannot overcome the difficulties caused by these differences. They use terms like "the pregnant female" and "the developing fetus" as if they were equivalent states among species, which of course is not true.
Many Yerkes studies have addressed "the behavioral effects" of cocaine and other drugs.49,53-58 Typically, their protocols involve shining a light for a set period of time, turning it off, and then giving the monkey two or three seconds to pull a lever to avoid an electric shock. For example, Leonard Howell and W. Morse found that low and intermediate cocaine doses increased response rates, while high doses decreased response rates. Chronic cocaine administration greatly increased response rates. The authors have claimed that this study addresses the "disruptive effects of cocaine." However, it has long been known from clinical study that cocaine effects cognition and behavior, and the primate researchers contribute nothing new. The reinforcing effects of acute low and intermediate cocaine doses--since they do not result in cognitive disorganization--improve performance, as is the case in humans. Acute high doses--causing more cognitive disruption than behavioral reinforcement--interfere with performance, which is also the situation in humans. The improved performance found in nonhuman primates with chronic cocaine administration does not accord with human experience, in which chronic cocaine use causes performance deterioration for many reasons.
Byrd and Howell are attempting to understand the effects of cocaine on brain neurotransmitter systems. They hope to find agents to treat cocaine addiction by identifying drugs that might alleviate the cocaine withdrawal syndrome.1,57,58 They have hypothesized that symptoms of cocaine withdrawal arise from a depletion of the neurotransmitter dopamine caused by chronic cocaine use, and that restitution of dopamine levels would therefore reduce cocaine craving during withdrawal.58 In addition, they have suggested that this dopamine-depletion state is biochemically similar to depression.64 Rather than administering dopaminergic agents directly, which they consider to have too many side-effects, they have administered agents that reduce the levels of serotonin, another neurotransmitter, thinking that reduced serotonin levels may increase dopamine levels "just enough."64
There are many difficulties with these presumptions and suppositions.
First, there is no evidence that the biochemical effects of cocaine on
humans and rhesus monkeys are the same. Second, there are at least six
different types of dopamine receptors, the stimulation of which (by dopamine)
results in different neurological events.65 Third, humans
with dopamine depletion secondary to chronic cocaine use often show other
disordered neurotransmitter states, both from using other drugs and from
other psychological disorders that may accompany cocaine abuse. For example,
clinicians have documented excess of dopamine and psychosis, GABA depletion
and anxiety, norepinephrifle depletion and depression, acetylcholine
depletion and cognitive deficit, and serotonin depletion and aggressive
behavior. All of these neurotransmitters have been found to play a role
in depressed states, and all interact with dopamine.66 Fourth,
potent antidepressant drugs that successfully treat depression (fluoxetine,
paroxetine, sertraline) increase serotonin level; they do not decrease
it.67 Fifth, a drug that reduces serotonin level (cyproheptadine)
has been found to be useful in neither depression nor cocaine addiction.68 Sixth,
use of antidepressants (imipramine, desipramine) in the treatment of
cocaine abuse has shown only ambiguous results.68 Seventh,
use of drugs in humans that alter dopamine levels (bromocriptine increases
it, phenothiazines reduce it) has not been shown to significantly affect
addicts' use of cocaine.68 Eighth, in human depression, serotonin
is clearly more disordered than dopamine, and the "dopamine hypothesis
of depression," which the Byrd-Howell work seems to resurrect, is
obsolete? Ninth, elevated dopamine levels in many patients with schizophrenia
does not reduce the incidence of cocaine abuse in these individuals.70
7. Memory
Yerkes researchers contend that memory and recall can be studied most effectively
in nonhuman primates because they do not speak:
Since studies of memory have involved linguistically-competent human subjects, memory processes have been confounded with linguistic ability. Studies on human and animal memory have demonstrated remarkable similarities in human and nonhuman memory processes, and they indicate that fmdings derived from animal experiments, which are not confounded by linguistic ability, can enhance our understanding of human memory.71
With this explanation in mind, they are attempting to produce, in aged rhesus monkeys, a 'valid animal model of memory. . . for developing and testing strategies to alleviate severe memory impairment."71
There are several flaws in this thinking and, therefore, difficulties with the goals. The contention that rhesus monkeys do not possess linguistic ability contradicts the Gouzoules' claim that monkeys' vocalizations show "rudimentary. . . similarities" with "certain aspects of human language."1 If Byrd and Ellis are correct, the Gouzoules' studies are invalid. If the Gonzoules are correct, Byrd and Ellis' basic premise is incorrect.
It makes no sense to strip from the study of human memory the single characteristic that many cognitive biologists consider to be the fundamental characteristic of human consciousness--language72 It is so basic that William James considered it to be an instinct,73 and Noam Chomsky, echoing the concept of language's instinctual nature, has contended that its development in human beings is innate.74 Language variation has been found to parallel genetic variation across the globe.75 And, modern neurological theory has posited that memory is primarily an emotional, not cognitive, experience involving the limbic system76--an experience that cannot be understood by studying cortical function alone." It can be argued that, since language is such an integral part of human consciousness, consideration of language is mandatory in the understanding of human memory, not a "confounding" variable. In addition, language is required for the experimental subjects to relate their mental states to investigators. If Byrd and Ellis are correct about the absence of linguistic features in the vocalizations of rhesus monkeys, and many scientists believe they are,78 then these monkeys cannot model human memory. If they are incorrect, their findings stem from a basically incorrect premise. In any case, they have not demonstrated sufficient analogy or homology between human and rhesus monkey mentation to warrant such investigations.
Similarly, Yerkes researchers have not mimicked human memory loss in monkeys; they have not identified naturally occurring, pathological memory loss processes in monkeys. In fact, their research has revealed basic differences between the aging human and rhesus monkey brain. The salient feature of aging in the human brain is gradual neuron loss, but this does not appear to be the case in aging monkey brains.79 While Yerkes researchers have failed to create a valid model of human age-related memory loss, progress in this area has instead relied on human patient studies.80
Byrd and Effis commit the same ontogeny-phylogeny and reductionistic errors of other behavioral primatologists, including Tomasello, Gouzoules, and Rumbaugh, by implying that monkeys are like primitive humans. Consequently, they assume that their research elucidates the genetic contributions to memory that humans and monkeys share. They assert "pure" (i.e., genetically based or "hardwired") memory--shared between monkeys and humans--can be studied free from the presumably contaminating influence of language and culture. Information about the neurophysiological memory apparatus that humans and monkeys share, the Yerkes team believes, can then be applied to human aging problems and then altered with pharmaceutical agents. However, human memory is a distinctly human experience, and, in addition to language, involves a distinct human culture. Memory in rhesus monkeys is fundamentally different from that of humans because of the former's non-linguistic thought processes and different cultural experiences. Implicit in this research are the invalid assumptions that humans, but not monkeys, have continued to evolve culturally for millions of years, and that genetic contributions to language have not evolved significantly.
The methodology of studying human experiences, such as memory, happiness, sadness, or indecisiveness, through physiological investigation attempts, by reductionistic methodology, to identify the physiological bases of human mental experience. This approach, known as experimental psychology or physiological psychology, has been severely criticized by some practitioners as being fundamentally flawed--a "contradiction in terms." 81,82 It aims to "understand" psychological processes by reducing them to their physiological components, thereby appearing to lend greater scientific credibility to data. In actuality, however, this technique of investigating behavior merely reprocesses already known human phenomena into a "new" animal behavioral format. In doing so, integration and theory are sacrificed for technical sophistication, and the essence of the phenomenon being studied vanishes. Byrd and Ellis' studies represent this kind of investigation, and their data cannot elucidate the human characteristic(s) under investigation.
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