With the expansion of his theory and the TCI psychological assessment in 1993, Cloninger veered significantly toward a more purely philosophical direction, advancing claims that were difficult to substantiate empirically. In his 2004 book Feeling Good: The Science of Well-Being, Cloninger presents ideas that end up being more humanitarian-positive psychology, with insufficient substantive brain science. His prescriptions become more sensible guides for living than evidence-based psychobiological inferences.
To his credit, Cloninger has assembled a fine personality instrument. However, while it may be one of the better instruments for diagnosing personality disorders (Farmer & Goldberg, 2008b), it is by no means the only good instrument available in this arena. One might have wished that Cloninger had attempted to refine the bottom-up neurobiological aspects of his original theory. Instead, he attempted to expand toward a more top-down approach to understanding human well-being.
Altogether, Cloninger is a creative scholar who has enlivened the field with novel perspectives, reflecting the consideration of an incredible range of information, including recent participation in a far-reaching genetic analysis of schizophrenia (Arnedo et al., 2015). However, he has yet to provide a biological theory of personality that adequately accounts for the fundamental affective infrastructure of mammalian brains.
At this point, Darwin’s famous theoretical dictum about mammalian mental differences being “of degree not of kind” seems to be holding true in the world of personality theory. Along these lines, it is interesting that Cloninger has not focused on the Big Five Conscientiousness dimension as a possible cortically based character trait that may acquire the capacity to regulate subcortical primary emotions. Among the great affective neuroscience puzzles that needs more experimental attention is the developmental construction of this Conscientiousness regulatory trait, which, we assume, appeared on the neuroevolutionary scene long before the emergence of Homo sapiens.
The cortex, with its massive capacity to learn, provides vast diversities of mental life that are truly unique to each individual. Yet, such differences emerge from the shared emotional and other affective features of our personalities, based robustly on survival systems that evolved long before humans walked the face of the earth. That the intrinsic genetic and developmentally guided epigenetic strengths and weakness of these systems are critical for the emergence of our higher-order characterological traits seems more likely than ever, which leads us to the subject of the next chapter.
CHAPTER 15
Genetics and the Origins of Personality
Owing to the imperfection of language the offspring is termed a new animal, but it is in truth a branch or elongation of the parent; since a part of the embryon-animal is, or was, a part of the parent; and therefore in strict language it cannot be said to be entirely new at the time of its production; and therefore it may retain some of the habits of the parent-system.
—Erasmus Darwin, Zoonomia; Or, The Laws of Organic Life
We are survival machines—robot vehicles blindly programmed to preserve the selfish molecules known as genes. This is a truth which still fills me with astonishment.
—Richard Dawkins, The Selfish Gene
IN RECENT ACADEMIC HISTORY, the genetic foundations of human personality has been a contentious issue, almost as difficult for many to digest as the heritability of intelligence. To suggest that one’s affective temperamental ways of being in the world could be influenced by genes was often seen as an odious way of envisioning human nature, and individuals who did so in voluble ways were commonly targets of gentle as well as strident ridicule. Of course, the classic view, from Hippocrates to Galen, was that individual differences in personality (although not called that) could be inborn, as reflected in individual temperamental variability, which was presumably controlled by basic body humors, which led people to be choleric (angry, irritable), melancholic (sad, depressive), phlegmatic (calm, unemotional, with a touch of “coldness”), or sanguine (joyful-sociable), because of their balance of distinct bodily humors. Of course, this useful scheme is now considered a historical curiosity.
Perhaps the most recent, now historically memorable example was The Bell Curve: Intelligence and Class Structure in American Life (1994), in which two eminent scholars, Richard Herrenstein, a professor from Harvard, and Charles Murray, asserted that “smarts” were inherited largely from smarter parents, with overtones that both social class and human diversity around the world were related to intrinsic aspects of intelligence.
Herrenstein (1930–1994), a student of B. F. Skinner, died before the commotion their book fermented fully materialized. Murray, a political libertarian and social pundit who initiated the project, has lived through the brouhaha that ensued. Reverend Jesse Jackson critiqued their effort as little more than “recapitulation of ancient garbage,” while President Bill Clinton argued their thesis “goes against our entire history and our whole tradition” (Sesardic, 2005). Of course the view that “genes count,” with practical consequences for all physical as well as psychological traits, has in the ensuing quarter century become accepted general knowledge, but the details have only begun to be fleshed out. And as the science of heritability has matured, new twists have been revealed (e.g., epigenetics, discussed below), making the whole topic more subtle and interesting. As we highlight here, gene expression can be dramatically molded by a host of environmental, internal chemical, and perhaps even brain emotional variables (i.e., strong, real-life experiences).
Modern genetics has revealed a Pandora’s box of genetic rules, with all arguments needing to be tempered by the accruing evidence. Our goal in this chapter is to provide a snapshot of the evidence genetic analyses provide for scholarly discussion in this formerly contentious area, amplified by more recent epigenetic evidence, which has now highlighted how environmentally modulated gene expression, some of which can last a lifetime (and be passed on to offspring), adds layers of complexity to comparatively simple genetic inheritance (for a review, see, e.g., Montag et al., 2016; Montag & Panksepp, 2017; Montag & Reuter, 2014). The fact that supportive and stressful social environments can modify gene expression patterns is especially fascinating and important for the way we rear our children. But before we dip into the complex discussion of possible epigenetic controls, we focus on the classic behavioral evidence for genetic foundations of human personality.
HERITABILITY OF PERSONALITY
The traditional way to pursue this issue has been to contrast personality similarities and differences between children from the same families, with the very best data coming from the contrasting of personality traits in identical and nonidentical twins. A great deal of data exist indicating that human personality traits are highly heritable (Turkheimer, 2000), which was confirmed by extensive analyses concluding that all human traits are heritable (Montag et al., 2016; Polderman et al., 2015).
However, perhaps driven by social forces striving for gender and racial equality, as well as perpetuating a cognitive-behaviorist tradition in psychology, there remains a bias for cognitive learning theory and against genetic and epigenetic explanations, as historically characterized by a quotation from Walter Mischel: “Genes and glands are obviously important, but social learning also has a dramatic role. Imagine the enormous differences that would be found in the personalities of twins with identical genetic endowments if they were raised apart in two different families” (1981, p. 311).
Remarkably, the Minnesota Study of Twins Reared Apart took on this challenge to find out to what extent identical twins would retain their similarity if raised in different families. In 1988 the project published a study (Tellegen et al., 1988) affirming that, in contrast to the expectations of many psychologists, identical twins reared together did not have more similar personalities than identical twins separated very early in life (at a median of 2–3 months) and reared apart (with a median total separation of 33.8 years). In both cases “about 50 percent of measured personality diversity can be attributed to genetic dive
rsity” (p. 1035). These authors further reported that the shared family environment generally played a modest role in determining personality traits, one exception being a small but significant shared environmental influence for the Social Closeness scale from the Multidimensional Personality Questionnaire (Tellegen, 1982), which measures the tendency to be warm and affectionate and to value close personal ties and turn to others for comfort and help.
These revealing studies continued beyond the realm of typical personality measures. Waller, Kojetin, Bouchard, Lykken, and Tellegen (1990) further showed that identical twins reared together or apart exhibited very similar Religiosity, a measure of religious commitment and engagement in such activities. Again, the genetic influences accounted for about 50 percent of the differences with shared environmental effects being negligible. Studying identical twins raised in different homes later showed that Religiosity was linked to Authoritarianism and Conservatism, all of which seemed to be aspects of the Traditionalism scale from the Multidimensional Personality Questionnaire, with differences accounted for by genetics consistently in the 50 percent range (Ludeke, Johnson, & Bouchard, 2013). Further pursuing the theme that all human traits are heritable, the Minnesota group (Lykken, Bouchard, McGue, & Tellegen, 1993) found again that about 50 percent of the variability of interests—including industrial arts, working with animals, buying and selling, accounting or mathematical interests, medical work, writing, and music—could be accounted for by genetics.
While these findings remain to be explained in any genetic detail, it is likely that our evolved individual variability, including personally oriented likes and dislikes coupled with our various inherited aptitudes, substantially influences how we respond to experiences in a grand endophenotype-environment interaction, which helps mediate and promote our developing temperament and interest patterns. To elaborate somewhat, this view was originally presented by Scarr and McCartney (1983) in a paper cited 1,420 times as of this writing. They proposed a behavior development theory asserting that our individual genotypes predispose us to select personally compatible environments, an “active” process that becomes increasingly prevalent as we mature and becomes more independent of our “passive” early child-rearing experiences. Specifically, they cited data that by late adolescence adopted siblings resemble each other less than previously when parental environments may have induced more similarity. Even nonidentical twin similarities begin to decline as their common early home environments give way to actively selecting experiences compatible with their individual genotypes.
Thomas Bouchard (1997) extended Scarr and McCartney’s position by coming closer to defining the mechanisms driving the selection of compatible environments from the diverse available possibilities. In explicating his Experience Producing Drive theory that genes drive personality-shaping behavior, Bouchard stated, “We propose that what are inherited are specific adaptive species-typical affective motivational systems shaped by the environment of evolutionary adaptiveness” (1997, p. 62). We couldn’t agree more, except to add that Bouchard’s “affective motivational systems” are most likely the emotional primary rewards and punishments guiding the learning and behavioral choices of all mammals in this grand evolved endophenotype-environment interaction that allows sentient beings to adapt to their worlds. In other words, it is our emotional affects that influence our perceptions and bias our approach or avoidance of potential environmental experiences, such that one person finds backpacking in the wilderness an exciting possibility while another recoils at such a frightening venture and yet a third dismisses the idea as a childish distraction, all reflecting and amplifying our personality differences.
HERITABILITY OF THE CLASSIC BIG FIVE
For the classic Big Five personality traits (Extraversion, Agreeableness, Conscientiousness, Emotional Stability, and Openness to Experience), diverse studies during the past half century have confirmed robust genetic as well as environmental foundations for all five personality dimensions, approximating the classic 50 percent genetic influence, a finding confirmed by a meta-analysis (Vukasovic´ & Bratko, 2015). Indeed, six factors of the neuroemotionally inspired Affective Neuroscience Personality Scales (ANPS) scales could be conceptually related to the Big Five. For instance, we evaluated how emotional-personality self-reports on the ANPS related to the Big Five factors (Davis et al., 2003; Davis & Panksepp, 2011). As described in Chapter 2, each ANPS factor significantly related to one of the Big Five personality factors. Accordingly, we postulated that the core emotional systems (SEEKING/Enthusiasm, RAGE/Anger, FEAR/Anxiety, CARE/Nurturance, PANIC/Sadness, and PLAY/Joy) developmentally contribute to the emergence of the Big Five, thereby potentially providing a basic neuroemotional foundation for the psychology-only Big Five tradition.
Accordingly, with the analysis of primary emotional systems of mammalian brains, on which the ANPS was premised, one has novel ways to link the genetics of primary emotions revealed by animal research to Big Five personality dimensions derived strictly from human research. Still, there are few direct analyses of such relationships in humans. However, a collaborative study of both scales was conducted with the leadership of our German colleagues (Montag et al., 2016), who evaluated 303 identical (monozygotic) twins (77 percent female) and 172 nonidentical (dizygotic) twins (65 percent female) and found significant (moderate to strong) influences of genetics on these scales. The lowest heritability estimate was evident for the SEEKING urge (30 percent), perhaps because it influences so many basic behaviors and emotions, and highest was for PLAY (63 percent). It is worth reiterating that many personality studies during the past half century have indicated comparably robust genetic foundations for all of the Big Five traits (Johnson, Vernon, & Feiler, 2008). The Montag et al. (2016) study further highlights the usefulness of the ANPS for biologically oriented personality research such as confirming that depressed people have lower SEEKING values than nondepressed individuals as has been predicted from various animal studies (e.g., see Panksepp, 2015, 2016).
GENETIC PATHS TO PERSONALITY DEVELOPMENT?
Abundant evidence has long existed that personality has a strong genetic foundation (for a synopsis, see Montag & Panksepp, 2017). The heritability of human personality is well captured by encapsulated human wisdom in such phrases as, “She is just like her grandmother,” or “He’s just like his father.” Animal breeders have long understood that through a knowledge of the parent’s psychological temperaments, as well as their more obvious physical characteristics, they can effectively breed for many psychological as well as physical traits. These cultural truths and historical traditions in personality research are now being clarified and magnified not only by modern genetic studies of how temperamental traits can be transmitted but also by the fact that environment can have dramatic effects on how individual genes are activated or deactivated, namely, via epigenetic effects from one’s social-emotional environment to environmental toxins, land infertility, or even weather fluctuations leading to famines (Skinner, 2015).
To provide an historical perspective, with the emergence of modern molecular genetics and with the definitive acceptance that DNA constitutes the molecular underpinning of inheritance, in the early 1950s Watson and Crick (1953) provided the capstone in that argument by working out the coiled structure of DNA (work that earned them the Nobel Prize in 1962). Almost until then, contrary to compelling evidence provided by Oswald Avery’s group a decade earlier (Avery, MacLeod, & McCarty, 1944), most biologists believed that proteins were the proximal source of our heritability mechanisms. By the mid-1950s, after Crick and Watson beat Linus Pauling to working out the structure of DNA, everyone had accepted that the critical molecules were sequences of nucleotides in DNA (adenine, cytosine, guanine, and thymine) that could code for various messenger RNAs in various permutations (e.g., thymine being replaced with uracil), which provided the “triplet codes” for proteins that were the most manifest conveyors of inheritance. Eventually Marshall Nirenberg at the National Institutes of Health illuminat
ed the triplet code for DNA and RNA, where three successive nucleotides coded for each of the twenty standard amino acids—he along with Gobind Khorana and Robert Holley received the Nobel Prize in 1968 for “breaking the genetic code.” Only gradually did it come to be realized that Mother Nature had devised ways in which environmental events, both social and inanimate, could modulate how intensely genes were expressed, which is what epigenetics is about—that term literally means “above or beyond genetics.”
This knowledge is changing the face of evolutionary psychology in ways that would amaze Charles Darwin, who first presciently plotted the paths of evolution that are now highways of solid knowledge. Clearly, this knowledge, in conjunction with modern illumination of brain circuits and neurochemistries, has enabled more lasting and ever deeper insights into the neurobiological foundations of brain systems that control animal and human nature as well as nurture, from genetics and epigenetics to social learning.
In short, this work has now affirmed the genetic foundations of our diverse personalities, both in humans and in other animals, which remain tethered to a grand ancestral heritage, but also how the foundations can be changed epigenetically through the way the genetic code can be played in different environments. Such work will eventually enrich our understanding of the basic affective foundations of human personality that lie within the deeper subcortical brain regions shared by all mammals (and many shared with all other vertebrates). Modern genetics also suggests there are genetic tethers to our cognitive abilities (for the IQ report from the Minnesota Study of Twins Reared Apart project, see Bouchard, Lykken, McGue, Segal, & Tellegen, 1990), but that is less well understood and, we assume, less important for understanding basic personality dimensions. Our focus is on inherited traits that constitute our affective strengths and weaknesses and how they are molded further by various developmental/epigenetic processes. Thus, both the qualities of nature and nurture combine in the construction of our intrinsic personality strengths and weaknesses. This is currently clearest in subcortical neural systems that are most critical for our affective lives, rather than in more purely cognitive (information-processing) qualities of our upper minds. But first, we share a few more reflections on basic genetics.
The Emotional Foundations of Personality Page 30