Personality Research on Great Apes
There can be no doubt that the difference between the mind of the lowest man and that of the highest animal is immense. An anthropomorphous ape, if he could take a dispassionate view of his own case, would admit that, though he could form an artful plan to plunder a garden—though he could use stones for fighting or for breaking open nuts—yet that the thought of fashioning a stone into a tool was quite beyond his scope. Still less, as he would admit, could he follow out a train of metaphysical reasoning, or solve a mathematical problem, or reflect on God, or admire a grand natural scene. Some apes, however, would probably declare that they could and did admire the beauty of the colored skin and fur of their partners in marriage. They would admit that though they could make other apes understand by cries some of their perceptions and simpler wants, the notion of expressing definite ideas by definite sounds had never crossed their minds.
Nevertheless the difference in mind between man and the higher animals, great as it is, certainly is one of degree and not of kind.
—Charles Darwin, The Descent of Man
TO HELP HIGHLIGHT the continuity of personality construct across species, we devote this chapter and the next two to three species: the one that is evolutionarily closest to us (chimpanzees), the one with whom we have historically had the closest relations (dogs), and one that has brought us much misery historically (plagues) yet also has served us so well in medicine and neuroscience (rats). We also briefly touch on those vertebrates that are about as distant from us as any other living vertebrate species (fish). Our hope is that this progression will help readers appreciate the gradients of personality that reach far back in evolutionary time, even as the neuropsychological (albeit not the behavioral) details get harder and harder to fathom as the evolutionary distance between ourselves and other species increases. We provide some detailed coverage for students of personality, although general readers may wish to pass over some materials.
OUR CLOSEST LIVING EVOLUTIONARY RELATIVE
Chimpanzees are the closest living phylogenetic relatives of human beings. Humans share approximately 98.8 percent of our DNA with chimpanzees (Chimpanzee Sequencing and Analysis Consortium, 2005), and a recent analysis suggests humans and chimpanzees may share a common ancestor as recently as 4 million years ago (Hobolth, Christiensen, Mailund, & Schierup, 2007). Therefore, to the extent that personality is influenced by brain biology, one would expect chimpanzees to exhibit the most similar personalities to humans among the vast varieties of nonhumans with which we share this planet.
Indeed, many have explored how similar chimpanzees and humans actually are. Frans de Waal has written that chimpanzees form political alliances to help them maintain power and status within their social group (de Waal, 1982) and exhibit dispositions for moral behavior (de Waal, 1996). Chimpanzee cultural differences between social groups have also been described, including the use of medicinal plants (McGrew, 1992, 2004). Jane Goodall documented chimpanzees making tools and hunting small mammals (Goodall, 1986). While Goodall, in a manner of speaking, moved right into the homes of wild chimpanzees in Africa, others have adopted chimpanzees into their homes and raised them like their own children. The most famous of these human chimp parents were Allen and Beatrix Gardner (a student of Nobel Prize–winning ethologist Niko Tinbergen), who adopted Washoe into their home and taught her to communicate with them in American Sign Language. The pioneering chimpanzee researcher Robert Yerkes (1925) believed that chimps understood many of his words and had speculated that chimpanzees might learn to sign, but apparently no one ever tried to formally verify that until the Gardners. Since that pioneering work, many have now taught chimpanzees (and gorillas) to communicate using sign language or sign language equivalents.
CHIMPANZEE PERSONALITY AND BIG FIVE CONSCIENTIOUSNESS
Up to this point in the book, we have only discussed the Big Five Conscientiousness dimension with respect to humans. In fact, in studies using ratings of mammals using personality inventories, a Conscientiousness dimension had been lacking (Gosling & John, 1999)—until James King and Aurelio Jose Figueredo of the University of Arizona set out to answer the question, “How closely do chimpanzee personality factors resemble those in humans?” (King & Figueredo, 1997, p. 257), by attempting to verify that all of the Big Five personality factors could also be measured in chimpanzees.
Mostly drawing from Goldberg’s (1990) Big Five personality taxonomy, King and Figueredo selected forty-three descriptive adjectives and used fifty-three experienced observers to rate one hundred chimpanzees from twelve zoological parks, obtaining an average of over four observer ratings per chimpanzee. A factor analysis of these mean observer ratings yielded six factors, with Dominance emerging as the first and largest factor, which was later determined to be highly heritable in chimpanzees (Weiss, King, & Figueredo, 2000). Factors 2–6 corresponded to the human Big Five: Surgency/Extraversion, Dependability/Conscientiousness, Agreeableness, Emotionality/Neuroticism, and Openness to Experience, although the Emotionality and Openness factors were small, containing only three and two items, respectively. Confirming the validity of their findings, each of these factors except Openness was later shown to be related to behaviors that were independently observed in zoo settings (Pederson, King, & Landau, 2005). Indeed, for the first time a research team had objectively documented Conscientiousness, as well as the full Big Five personality model, in a nonhuman species, with the wrinkle that Social Dominance was added to the mix, and they had done so by obtaining ratings of adjective trait terms originally used to describe human personalities.
King was also the lead author in a second factor-analytic study using all new chimpanzee subjects, combining forty-three nonzoo chimpanzees living in a large African sanctuary in the Republic of the Congo with seventy-four chimpanzees living in nine zoos in the United States and Australia. In this second study, the same forty-three descriptive adjectives were used to rate the chimpanzees, although, the adjectives for the African sanctuary chimpanzees were translated into French. Even with this heterogeneous group, including nonzoo chimpanzees with French-speaking raters, all six of the previously identified chimpanzee dimensions, including Conscientiousness, were obtained in this second study. However, the small Emotionality/Neuroticism and Openness factors did not meet statistical standards for replication, although most items loaded the same on these two factors in both studies (King, Weiss, & Farmer, 2005). The authors concluded they needed more items on these two factors. Yet, their structure of chimpanzee personality, as revealed by factor analysis, remained relatively constant across the two studies of different chimpanzees regardless of the different environments, which was consistent with a biological basis for personality and suggested that environmental effects on chimpanzee personalities may be relatively small.
This smooth sailing was short-lived, as a shift to orangutan subjects failed to identify a Conscientiousness factor. Although there had been an earlier failure with gorillas (Gold & Maple, 1994), with two chimpanzee successes behind them Weiss, King, and Perkins (2006) tried their hand in another large-scale study with 152 zoo-housed orangutans. The same methodology and rating instrument—expanded with five additional adjectives—replicated all of the chimpanzee dimensions except Dependability/Conscientiousness and Openness. It was largely these two dimensions that blended into the fifth factor, which Weiss and colleagues labeled Intellect based on its highest loading item, “intelligent,” as well as “disciplined” from the Dependability dimension. Other adjectives identified with Dependability in the chimpanzee studies tended to load either on their Neuroticism factor, as with “impulsive,” “cautious,” “erratic,” and “unpredictable,” or on their Dominance factor, as with “persistent” and “reckless.” One hypothesis for the failure to find a Dependability/Conscientiousness dimension was that the capacity for regulating the expression of aggression and irritability was not as highly developed in the orangutan, and therefore, such traits were expressed more purely as Social Dominance.
The authors also argued that the inability to replicate the Dependability factor in orangutans could suggest either that the Dependability/Conscientiousness capacity first emerged evolutionarily with chimpanzees or possibly that the conscientious regulation of especially negative primary emotions was less critical in the semisolitary orangutan. That Gosling and John (1999) were unable to identify a Conscientiousness factor in any species other than chimpanzees supported the argument that Conscientiousness first appeared in chimpanzees. However, the Darwinian principle of continuity as applied to mental functions in animals would argue for the possibility that aspects of Conscientiousness should be identifiable in orangutans and other even more distantly related species. Clearly, further work would be required to resolve such issues.
Subsequently, two additional chimpanzee studies using the original forty-three King and Figueredo (1997) items fully replicated the first four factors (Dominance, Surgency/Extraversion, Dependability/Conscientiousness, and Agreeableness) but had similar problems demonstrating statistical congruence for the last two factors (Emotionality/Neuroticism and Openness). In the first case, Weiss, King, and Hopkins (2007) added 102 new zoo animals and 175 chimpanzees housed in the Yerkes National Primate Research Center. Later, Weiss and King also teamed up with a group of five Japanese scientists (Weiss et al., 2009) to examine the personalities of 146 chimpanzees living in Japanese zoos, research institutes, and a sanctuary. Despite the same problem of not being able to statistically replicate the Emotionality/Neuroticism and Openness factors found in the original King and Figueredo (1997) report, all four studies had demonstrated a statistically replicated Conscientiousness factor. In addition, the Japanese study, in which all ratings were completed using the forty-three-adjective scales translated into Japanese, also confirmed the finding from the Republic of the Congo report that chimpanzee personality ratings were not affected by the culture of the raters, which further underscored the biological foundation of personality.
Others had pursued alternate paths to solving the chimpanzee personality puzzle. Working with Samuel Gosling, Hani Freeman wrote a dissertation that included the development and validation of a new chimpanzee personality rating scale. Her approach was to combine some adjectives from the King and Figueredo (1997) with additional trait descriptions that were unique to chimpanzees (Freeman et al., 2013). Her team tried to eliminate most redundancy and was able to reduce the list of traits to forty-one, which she used to collect ratings on ninety-nine chimpanzees at the University of Texas. In analyzing the data, several criteria finally led her to extract six factors. However, only the first five were interpretable: Reactivity/Undependability, Dominance, Extraversion, Openness, and Agreeableness. Because her Reactivity/Undependability dimension was very similar to King and Figuerado’s Dependability factor, she had once again demonstrated a Conscientiousness factor in chimpanzees. The remainder of her first five factors were also similar to the King and Figueredo dimensions, except that she lacked an Emotionality/Neuroticism factor. In the Freeman et al. study, the items that would have been expected to define a Neuroticism dimension loaded on either the Reactivity/Undependability or Dominance factors. So once again, the replication of King and Figueredo’s human-like Big Five plus Dominance chimpanzee personality structure remained illusive.
This story of searching for distinct personality dimensions in chimpanzees using factor analysis again demonstrates the vicissitudes of factor analysis in defining a biologically based taxonomy of personality. The first four of these chimpanzee studies suggested that results more congruent with the Big Five model would likely have been obtained if they had started with a larger, more representative pool of adjective descriptors. Even though that may be true, our position is that it is time to accept the limits of factor analysis and recognize that the next round of progress in understanding the dynamics of mammalian personality will likely emerge from an affective neuroscience analysis of how the mammalian brain responds—especially how the subcortical brain responds—to significant life events. A major theme of this book is that the remarkable homology of personality traits across mammalian species has its origin in the subcortical emotional systems of the brain, and a better understanding of these systems will be essential for discovery of the evolutionary sources of personality structures, perhaps even the sources of “human nature” from emotional pathologies to self-actualization. Indeed, this has been supported recently with Affective Neuroscience Personality Scales studies of human diverse human personality disorders (Karterud et al., 2016), discussed further in Chapter 18.
THE ANALYSIS OF ANOTHER PRIMATE
The effort to “discover” the human Big Five in the personalities of nonhuman primates took an interesting turn when Alexander Weiss of the University of Edinburg joined with F. Blake Morton and an international research team to study brown capuchin monkeys (Sapajus apella), a New World species that diverged from the human line a bit further down the evolutionary tree but one, like the Old World great apes of Africa and Asia, that has a large brain for its body size (Morton et al., 2013). Another important consideration in the project was using a revised King and Figeredo (1997) rating questionnaire called the Hominoid Personality Questionnaire, which had now been expanded from the original forty-three to fifty-four adjectives and that allowed them to better capture the Emotionality, Openness, and Conscientiousness dimensions (Weiss et al., 2009).
In this project, 127 captive brown capuchin monkeys from six sites were rated. The authors determined that their data did fit a five-factor solution, but they added further conceptual complexity to the discussion. Briefly, Morton et al. (2013) labeled their five factors Assertiveness, Openness, Neuroticism, Sociability, and Attentiveness, while acknowledging that their Assertiveness factor closely resembled King and Figueredo’s (1997) original chimpanzee Dominance factor, their Openness factor was similar to King and Figueredo’s Openness factor but also resembled the orangutan Extraversion factor (Weiss et al., 2006), their Neuroticism factor closely resembled the King and Figueredo’s Emotionality dimension, their Sociability factor shared elements of King and Figueredo’s Agreeableness and Surgency/Extraversion factors, and their Attentiveness factor most closely resembled the Conscientiousness dimension found in Japanese chimpanzees rated on the full Hominoid Personality Questionnaire by Weiss et al. (2009).
Despite these complexities, by using an expanded set of rating items, the Morton group had remarkably demonstrated Conscientiousness in capuchin monkeys, an evolutionarily older species than chimpanzees, even though earlier efforts to identify a Conscientiousness factor in gorillas and orangutans had failed to do so. This demonstration is important from a Darwinian continuity perspective and may open the way for others to look for elements of Conscientiousness even in nonprimate species. However, illustrating the difficulties of factor analysis, they failed to fully replicate the King and Figueredo (1997) Dominance factor and their Sociability factor structure blended elements of the Big Five Agreeableness and Extraversion dimensions.
BACK TO BASICS: ALTERNATIVE APPROACHES
Diane Dutton of Liverpool Hope University in the United Kingdom also developed a new personality rating scale for chimpanzees, but she started from the ground up, so to speak. That is, instead of building on an existing instrument, she used the expert knowledge of people working closely with chimpanzees and a technique developed by the American psychologist George Kelly (1955) to build a new set of rating items. In short, Dutton asked raters who had worked extensively with a group of twenty-four chimpanzees housed in the Chester Zoo to independently generate bipolar descriptors of chimpanzees, such as “aggressive-submissive,” to describe differences in pairs of chimpanzee they had worked with (Dutton, Clark, & Dickins, 1997). Using such descriptors generated by expert chimpanzee observers, she intended to devise a rating scale that would be more naturalistic and perhaps more appropriate for rating chimpanzee personalities. Eventually, she produced a forty-six-item personality rating scale for chimpanzees and coordinated a study of seventy-five captive chimpanzees living in seven zoological parks in Europe, the United States, and South Africa (Dutton, 2008).
Using factor analysis, she extracted five factors that she labeled Agreeableness, Dominance, Neuroticism, Extraversion, and Intellect. Her factors included many similarities with our Affective Neuroscience Personality Scales. For example, her Agreeableness dimension included items such as “protective toward infants” and “interacts with infants and juveniles” plus “reconciles others” and “reassures others,” all of which are consistent with the CARE system. Her Neuroticism dimension included “nervous,” “easily frightened,” “fearful for no apparent reason,” and “anxious,” all of which suggest the FEAR system. The Extraversion dimension included “playful” and not “withdrawn,” which fit with the PLAY system. The Intellect dimension included SEEKING concepts such as “inquisitive” and “investigative.” With the Dominance dimension having its highest loading on “aggressive,” which is suggestive of the RAGE/Anger system, she had scales representing each of the personality-related blue ribbon emotional brain systems except PANIC/Sadness. In other words, she may have independently discovered the emotional foundations of personality in our closest evolutionary relative.
Interestingly, Dutton did not derive a Conscientiousness scale, an omission we touch on again shortly. However, in using rating items grounded in actual observations of chimpanzee natural behaviors, Dutton seems to have confirmed a theme we emphasize in this book: Relying on measures as close to the primary expression of emotional behaviors as possible is likely to keep researchers close to basic neural-system taxonomies of personality and keep them from deviating far from the foundational processes that help constitute even human personality.
“CONSCIENTIOUSNESS” CONSIDERATIONS
Conscientiousness in Big Five terms applied to humans has typically been described with such adjective pairs as “organized versus disorganized,” “responsible versus irresponsible,” “reliable versus undependable,” and “thorough versus careless” (Goldberg, 1992) but has been difficult to identify in animal studies perhaps because of the abstract nature of these terms. By contrast, in demonstrating the first appearance of a Dependability/Conscientious factor in chimpanzees, King and Figueredo (1997) selected adjectives from Goldberg’s (1990) Conscientiousness factor descriptors that seem eminently concrete and observable, such as “impulsive,” “reckless,” “erratic,” and “disorganized”—each of which Hofstee et al. (1992) showed had its strongest loadings on Conscientiousness—plus included overtones of “defiant” and “aggressive,” which might speak to the importance of regulating social dominance because it plays such a key role in chimpanzee social life. Indeed, all five chimpanzee studies reviewed above that used the forty-three King and Figueredo (1997) adjectives identified these six adjectives on their Dependability/Conscientiousness factors to some degree.
But why was Dutton not able to find a Conscientiousness factor in her chimpanzee data? Perhaps because she unfortunately included only two clear Conscientiousness items in her forty-six statements, relying on “persistent” and “unpredictable”, which may not have had enough power by themselves to emerge as a sixth factor measuring Conscientiousness. King and Figueredo (1997) had included eight Big Five Conscientiousness items, four of which loaded most strongly on their Dependability factor, and six more Conscientiousness items were added to the revised fifty-four-item version of the Hominoid Personality Questionnaire that was used to identify a Conscientiousness factor in brown capuchin monkeys. Thus, it is likely that if the number of Dutton’s conscientiousness-type items had been expanded, her sample would have revealed a Conscientiousness dimension as well. Such are the vagaries of the factor-analytic world.
In any case, this first clear demonstration of the Big Five human personality dimension in a nonhuman animal supported Darwin’s continuity of species principle. Indeed, having demonstrated this trait in chimpanzees and then brown capuchin monkeys opens up the possibility that rudimentary forms of conscientiousness might be observable in other mammals, such as dogs and rats. Coming back to the idea that more concrete and observable descriptors were necessary to reveal conscientiousness in chimpanzees hints that even more direct interventions and measures might be necessary to identify this cognitive, regulatory dimension in other mammals, especially in even more distantly related mammals.
An intriguing neuroscience demonstration of what may be considered evidence of conscientiousness in rats was reported by J. P. C. de Bruin in 1990. He and other researchers had previously determined that lesions to the orbital prefrontal cortex increased social-agonistic interactions in rats, that is, made them more aggressive, which implied that the orbital prefrontal cortex exerted an inhibitory control over some brain region supporting the aggressive behavior. Research suggested the brain region was likely the hypothalamus. With this insight, de Bruin implanted electrodes in the hypothalamus of rats and observed whether aggression directed toward another rat was elicited by a small (40–60 microamp) current. Then, using a second prefrontal electrode, he concurrently stimulated the hypothalamus and various locations in the prefrontal cortex and determined that the greatest inhibition of hypothalamic-elicited aggression occurred when the prefrontal electrode was placed in a rat’s orbital prefrontal cortex. Both the lesion data and concurrent electrical stimulation data were consistent with the conclusion that the rat orbital prefrontal cortex “exerts an inhibitory control over hypothalamic sites from which aggression can be elicited by electrical stimulation” (de Bruin, 1990, p. 492). Could this inhibition of aggressive behavior from electrodes placed in the orbital prefrontal cortex represent an induced case of conscientiousness in rats? Clearly, there is a brain mechanism in place for inhibiting rat social aggressive behavior likely stemming from the RAGE/Anger system. How this inhibitory control might be learned and expressed in rat social behavior remains to be determined. It would also be important to link orbital prefrontal activity to “conscientious” behavior in other species. In any case, this intriguing demonstration hints of a rudimentary chimpanzee-like conscientiousness inhibiting social aggression in a species much less well endowed with cortical capacity than the brown capuchin monkey.
SOCIAL DOMINANCE
The emergence of a prominent Dominance factor in chimpanzees could be explained in part by “the pervasive role of dominance and power-related activities in the social order of wild chimpanzees” and “may be further enhanced in zoo habitats where dispersal is not possible” (King & Figueredo, 1997, p. 268). However, some have emphasized dominance as a basic human personality dimension. The Hogan Personality Inventory (Hogan & Hogan, 2007) similarly expands the Big Five with a sixth scale labeled Ambition that is characterized by “status” and “competitiveness,” and de Raad (1999) has also emphasized dominance as a human interpersonal personality dimension. Donne van der Westhuizen, a student at the University of Cape Town in South Africa working with Mark Solms, has written and published a dissertation exploring the possibility that social dominance might qualify as a primary emotion. Even though she reviewed a great deal of biological support underlying dominant and territorial behavior, her final conclusion was that there was insufficient evidence at present to classify social dominance as a primary emotion (van der Westhuizen & Solms, 2015), for dominance needs to be learned by actual social interactions. This does not mean that there are not specific brain systems that promote dominance (e.g., perhaps RAGE, LUST, and social SEEKING). In short, even though dominance is widespread throughout the animal world (including social relations in practically all mammals), we would argue that complex social learning is essential for it to manifest in the social world, and that early social PLAY is an important factor for finding one’s place in social structures (Panksepp, Jalowiec, DeEskinazi, & Bishop, 1985). In any event, much work remains to be done in the area of social dominance in mammals, including the manner of its emergence as a key feature of primate social life.
It is also noteworthy that not being “fearful” or “dependent” both loaded on King and Figuerado’s (1997) Dominance dimension rather than the Emotionality dimension, with a third adjective, “aggressive,” splitting its loadings between (high) Dominance and (low) Conscientiousness. In affective neuroscience terms these adjectives would be associated with FEAR, PANIC/Sadness, and RAGE/Anger, respectively. By contrast, in the King and Figueredo study the Emotionality dimension was limited to the more general and less specific terms “stable,” “unemotional,” and not being “excitable,” all resembling the relatively undifferentiated human Big Five Emotional Stability factor. Once again, one is compelled to address the limitations that factor-analytic procedures impose on parsing the workings of the mammalian BrainMind.
PRIMATE SUMMARY
Altogether, these primate studies establish that temperament in the great apes and brown capuchins can be accurately described using rating methods borrowed from human studies and resulting in the same factor-analytically derived dimensions as those derived using human subjects. Having some difficulty replicating an Openness dimension is not surprising given the illusiveness of the smallest of the Big Five factors even in human studies (Goldberg, 1990). More generally, unresolved issues surrounding Conscientiousness and whether it can be systematically monitored in orangutans and primates generally is bound to remain unresolved for some time.
Yet, none of the primate studies reviewed above included a dimension for PANIC/Sadness separation distress (Panksepp, 1998a), perhaps because relevant developmentally important social-isolation challenges were not studied in zoo-reared primates, or because overt SADNESS-related behaviors are rare in zoo environments, as in the death of an infant or social companion. Yet, socially induced comforts of social contact, mediated in part by brain opioid inhibition of the PANIC/Sadness system (Panksepp, Herman, Vilberg, Bishop, & DeEskinazi, 1980; Panksepp, 1981a), supplies the social glue that provides the cohesion observed in the troops of intensely social animals such as chimpanzees and brown capuchin monkeys. Without social bonding, which to a great extent is derived from brain opioid and oxytocinergic inhibition of the PANIC/Sadness system (Panksepp, Normansell, Herman, Bishop, & Crepeau, 1988) and the consequent alleviation of separation distress experiences, we would not likely observe these primate species living in social troops.
Again, it is our view is that primate temperament research (indeed, nonhuman personality research in general) could benefit from a framework for carving this psychological domain into neuroscientifically based basic emotion dimensions. Accordingly, we suggest that a cross-species affective neuroscience provides a new framework for understanding some of the major sources of personality structures across all mammalian species, and thereby may provide a more scientifically meaningful foundation for future progress than the statistical factor-analytic method that has so far been used to classify personality traits.
SUOMI AND MACAQUES’ EARLY EXPERIENCE
Before leaving the primates, we describe how Stephen Suomi’s research on early experience in rhesus macaques illustrates complexities that arise from variations in mothering—namely, expressions of the CARE system—can have on primate personality. Like Scott’s (1962) emphasis on critical periods of development, Suomi studied the behavior of neonates and juveniles, believing that relatively brief early experiences disproportionately influence behavior and temperament throughout the life-span, and showed that early social deprivation could increase emotional reactivity and impulsiveness. Expanding on Harlow’s work with total social deprivation (Harlow, Dodsworth, & Harlow, 1965), Suomi (2006) proceeded to explore a less severe social deprivation model in which rhesus infants were hand-reared for one month and then housed with same-age peers until six months of age. These laboratory hand/peer-reared rhesus monkeys exhibited stable social-emotional deficits, such as low social dominance, little exploration, fewer play bouts, less complex play, and greater adrenocortical and noradrenergic reactions to social separation. In general, these hand/peer-reared monkeys mirrored a “high-reactive” temperament type comprising about 20 percent of rhesus monkeys reared by their mothers in naturalistic settings and also shared characteristics with an “impulsive” type accounting for 5–10 percent of mother-reared rhesus monkeys, with more aggressive social encounters, low social dominance, and low serotonergic functioning (Suomi, 1997).
Research on polymorphisms of the serotonin transporter (5-HTT) gene revealed that hand/peer-reared rhesus monkeys carrying a single “short” allele of the 5-HTT gene were more emotional and distractible, with low attention and visual orientation (Champoux et al., 2002), and showed reduced serotonergic functioning and high levels of aggression (Suomi, 2006). These hand/peer-reared monkeys with a short serotonin transporter allele were also shown to become more aggressive juveniles than mother-reared monkeys with the short allele (Barr et al., 2003). Indeed, rhesus monkeys carrying either one or two short alleles that were mother-reared exhibited normal levels of aggression and serotonin metabolism, similar to rhesus monkeys carrying the long 5-HTT allele (Higley et al.,2000). Thus, typical highly supportive maternal rearing along with normal interactions with peers was able to protect individual monkeys from the effects of the psychopathology-promoting short allele that, like in humans, has more influence on personality when expressed in the context of stressful childhood upbringing (Caspi et al., 2003).
In another example of the influence of mothering on temperament, rhesus infants bred to be either highly emotionally reactive or normally reactive were cross-fostered to well-experienced mothers selected because they were either highly nurturing or normally nurturing. The high-reactive infants reared by the highly nurturing mothers exhibited more exploration and less psychological disturbance during weaning than all other combinations. When moved into larger social groups, these high-reactive monkeys reared by the very nurturant mothers also attained top positions in the dominance hierarchy, with high-reactive monkeys fostered to normally nurturing mothers moving to the bottom of the hierarchy. Furthermore, highly reactive females reared by the highly nurturing mothers exhibited the maternal style of the foster mothers (Suomi, 1997). Such nature-nurture complexities demonstrate the dynamic character of the BrainMind that seemingly defies simple explanations. It will be interesting to learn the extent to which these maternal-gene interactions influencing temperaments of these rhesus monkeys are related to socially induced epigenetic (i.e., gene expression intensity) changes as found by Michael Meaney’s ( 2010) work with rats—more on that subject in Chapter 15.
PRIMATE SUMMARY WITH A HUMAN PERSPECTIVE
One of the themes running through the personality/temperament literature is the predominance of factor analysis as the tool of choice for identifying basic personality traits. Beginning with Raymond Cattell (1943) and the eventual emergence of the Big Five human temperament factors, personality theory has become captivated by statistically derived “latent” factors, and animal temperament research has fallen in step. Our colleague and mentor John Paul Scott often repeated that statistics in psychology were just tools for determining the intensities and patterns of experimental/behavioral effects, as opposed to a way of identifying the biological sources of those effects. Perhaps we need to think of factor analysis as just a tool that, may have been more valuable during the “black box” era of psychology and is now superseded by the current explosion of neuroscience approaches that allow us to peer inside the brain and directly manipulate brain functions, such as basic emotional networks, which we have advocated to be major contributors to human and animal temperamental variability.
Early in the twentieth century, Walter Hess was a pioneer in providing temperament research with improved tools to directly observe the naturally evolved “factors” within the brain (for complete summary, see Hess 1957). Notably, if one can stimulate the subcortical brain in a particular anatomical location with a tiny and relatively crude input, and consistently observe the same coherent output, and repeat the process across many animals, and attain the same results, one can be confident that the input has activated an organized brain system worth investigating. By pursuing such research during the modern era, Jaak Panksepp (1971, 1998a, 2005) continued such lines of research and documented seven subcortical primary-process (innate) emotion systems in the brain: that he labeled SEEKING, RAGE/Anger, FEAR, LUST, CARE, separation-induced PANIC/Sadness, and PLAY, of which six (excluding LUST) are here advanced as most relevant for personality/temperament research. Using tools that Hess pioneered, each of these brain emotional states evoked with subcortical electrical stimulation are considered primal foundations for our core emotional feelings—instinctual emotional-feeling systems that are critical tools for living and perhaps the formation of personality traits.
But how can we know nonspeaking animals have any feelings at all? This Pandora’s box—the mystery of valenced experiences—was opened up in the middle of the twentieth century by two groups of investigators (Olds & Milner, 1954; Delgado, Roberts & Miller, 1954) using deep brain stimulation (DBS) to simply inquire whether one can obtain rewarding or punishing effects from such brain arousals. Jim Olds found powerfully rewarding sites in many regions below the neocortex (animals would voluntarily turn on the DBS), but not in the top of the brain that controls our sensory perceptions and thoughts. Delgado and colleagues found other sites that were punishing—animals would turn off the DBS applied to other nearby brain regions. Such effects have been found in all mammals, indeed, all vertebrates that have been studied (Wauquier & Rolls, 1976).
The working hypothesis is that such DBS studies empirically define brain systems that feel “good” and “bad” in various ways—they help define how various positively or negatively valenced states of mind arise from subcortical brain activities. Now more recent neuroscience tools are also available for further investigations, including optogenetics (light stimulation of the brain) and DREADD (designer receptors exclusively activated by designer drugs).
Thus, there is currently strong anatomical, pharmacological, and physiological evidence for these seven defined emotion systems in all mammalian brains. Several of these emotions have evolutionarily older roots (SEEKING, RAGE/Anger, and FEAR), which are evident in all vertebrates. But three (CARING, PANIC/Sadness, and PLAY) seem to be much more developed in mammalian brains. Each of these emotional systems can be aroused with DBS, and although they can operate independently, they surely interact with each ther in yet undetermined ways, as well as with a variety of higher BrainMind functions (secondary-level learning and tertiary-level thought processes) to increase the overall adaptiveness (survival ability) by interacting with diverse higher BrainMind processes (for fuller descriptions, see Panksepp, 1998a, 2005, 2010b, 2011a; Panksepp & Biven, 2012).
Much of the rest of this book is devoted to relating these ancestral emotional powers of the BrainMind to the fundamental personality infrastructures of human brains. However, we will first summarize work on the personality variability in dogs and rats—with less and less known as we progress down the phylogenetic “ladder.” (Ladder is a misnomer—no such ladder exists, just the genetic diversification of species, because it is difficult to identify a common vertebrate ancestor that survived the last mass extinction event, namely, the last of the big die-offs of the last 500 million years—the most relevant one for mammals being the Cretaceous-Paleogene extinction event, which occurred approximately 66 million years ago.) Nevertheless, the animal and human personality complexities will undoubtedly remain poorly understood until we are able to align the major constitutional temperamental factors studied by monitoring the linguistic-questioning/answering functions of human brains with the natural (evolved) emotional/affective functions of vertebrate (especially mammalian) brains.