I’m a Soul, Man: One Psychologist’s Reflection on Human Nature
“It is dangerous to show man too clearly how much he resembles the beast, without at the same time showing him his greatness. It is also dangerous to allow him too clear a vision of his greatness without his baseness. It is even more dangerous to leave him in ignorance of both.”
—Blaise Pascal (1659), Pensées, fragment 347
It’s an odd exercise, perhaps, to speculate on our own nature. When I have asked acquaintances to describe their beliefs about our essential make-up—whether we are we bodies only, souls within bodies, or . . . ?—their responses are frequently to say it’s a problem too difficult to imagine. Others provide a standard dual-entity belief, that a spirit or soul, that essential thing we are at our core, guides our bodies around in the course of our earthly lives.
For most, this is not something we spend a lot of time contemplating. And this reflects the fact that much of what we believe is given to us by some authority (parents, pastors, teachers, and others) and held, often for years, without much exploration, questioning, or testing. It may also be argued that questions of body and soul are key aspects of the mystery of our being, and should simply be accepted as such, without trying to unravel what is not ours to know. It may also be that many are not particularly concerned to know precisely how body and soul may interact.
Still, most of us develop personal theories (explicitly or implicitly) about ourselves, our nature and identity, and it is interesting to explore the origins of such theories. Many times, such theories are simply adopted in whole or in part, from what we have learned from respected persons or texts. Remarkably, studies show that such theories, and the beliefs they support, are only rarely examined in any detail, though they may form core understandings of ourselves and our world.
Nancey Murphy, who has written widely on issues of human nature, describes a quiz on human nature that she provides to seminary students and other audiences. 1 I reproduce it here to delineate some of the philosophical options:
Which of the following comes closest to your under-standing of human nature?
- Humans are composed of one “part”: a physical body (materialism/physicalism)
- Humans are composed of two parts:
- a body and a soul
- a body and a mind (dualism)
- Humans are composed of three parts: body, soul, and spirit (trichotomism)
- Humans are composed of one “part”: a spiritual/mental substance (idealism)
- Who cares?
She reports that most evangelical students and general audiences choose dualist or trichotomist answers, but in other audiences responses are much different. Among scientists (particularly those in biological sciences), most are physicalists, as are most secular philosophers. Christian philosophers are divided between dualism and physicalism. This lack of consensus is not new. In 1978, David Myers reported that a similar survey among members of Presbyterian congregations found that most lay leaders in the church held a dualistic view, whereas the majority of pastors held a physicalist understanding. 2
It would seem that a question so fundamental to our understanding of ourselves, our place in creation, and our ultimate destiny, must result in something more than a response of “Who cares?” (although Murphy argues that this response may actually reflect a biblical perspective), and that there must be some way to select from among the variety of philosophical perspectives available. It may seem strange, then, to hear a scholar like Murphy claim, as others have emphasized before, that “the Bible has no clear teaching here. This has made it possible for Christians in different eras to recognize a variety of views in the texts, and, perhaps more importantly, to have read a variety of views into the texts” 3 (italics in original).
Yet, significant implications follow for our self-understanding, our interpretation of our own and others’ behavior (particularly concerning aspects such as volitional behavior, emotion, personality, morality, and consciousness), our understanding of health and illness, even for what we choose to study about ourselves. 4 Within these implications lie the reasons why questions of the nature of human beings are vital not only for philosophers and theologians, but for psychologists and those in many related fields, as well.
CONTEMPORARY MODELS OF HUMAN NATURE
A critical question concerning human nature has been, “Do we possess a soul?” Such a question is still asked (and answered in the negative) by those advocating a purely materialistic view of humans and (answered in the positive) by those attempting to defend a Christian or biblically based anthropology against a materialist position. 5 For many Christian scholars and scientists, the critical question has changed somewhat. It may be of greater significance to ask, “What is the nature of the soul?”
I review here some of the currently held perspectives, with the caution that no consensus currently exists in support of any one position.
Firstly, dualist positions, modifications of René Descartes’ view that the soul (or mind) and the body belong to totally different orders of being, remain. Radical dualism holds that the mind/soul is separable from the body, and that our person (or personality) is identified with the soul. 6 Our soul directs our body’s activity, makes moral or immoral choices, and departs our body at the time of our death. Our body, then, is viewed as no more than a temporary and disposable vehicle for our soul.
In describing his own dualist stance, Stewart Goetz argues that we must give the notion of a separate substance, a soul, some credence, for the simple fact that so many people, now and throughout history, have a foundational belief in its existence. 7 As he states, “ordinary people are dualists,” so it should come as no surprise that in Christian and other religious traditions, dualism is assumed. Goetz takes seriously his and others’ introspective experience of “self” in concluding that he, and we, are more than our physical bodies, though we know that our soul has a causal interaction with body (in some not completely understood fashion).
William Hasker supports emergent dualism, arguing that traditional Cartesian dualism leaves too large a causal gap between mind and body. 8 Some mechanism or entity must exist to explain what it is, for example, that directs our conscious perception of the world around us. Where some, dubbed emergent materialists, have claimed that consciousness emerges from a sufficiently (and astoundingly) complex interaction of miniscule components (our neural structures), Hasker argues, in apparent accordance with materialist views, that mind (or consciousness) must be a product of underlying neural structure and function and cannot simply be added on. He recognizes the “risk” in siding with materialist assumptions in this claim. But to account for the unity of our conscious experience and to allow for the continuation of self after death, Hasker proposes that mind/soul describes an emergent individual arising out of biological machinery but as a separate entity/substance.
Reductive materialism remains a prominent assumption in many fields, particularly in the physical sciences. In part, this is due to historical successes in reductionist explanations. Breaking down complex structures into their component parts for analysis has led to greater understanding of many complex phenomena, from chemical interactions to bodily systems. In part, materialism is maintained through long-standing principles of theory construction, such as Occam’s famous razor, which instructs theorists to choose the simplest satisfactory explanation (in other words, not to assume the existence of entities or causal factors, like an immaterial soul, when explanations for an event are possible without such recourse). Reductive materialism holds that our human make-up is entirely physical and that psychological events (emotions, beliefs, volition) are or will be explained according to organic principles. Francis Crick, one of the discoverers of the structure of DNA, put it bluntly “ ‘You,’ your joys and your sorrows, your memories and your ambitions, your sense of identity and free will, are in fact no more than the behavior of a vast assembly of nerve cells and their associated molecules.” 9 He added, “The idea that man has a disembodied soul is as unnecessary as the old idea that there was a life force.” 10
Donald MacKay has referred to reductive materialism as “nothing buttery,” 11 that is, a claim that we are “nothing but” the sum of our biological elements. From such a perspective, it should be the case that when those elements and their interactions are fully understood, a complete understanding of more complex entities (such as ourselves) will be possible. MacKay counters that “nothing could be more fraudulent than the pretense that science requires or justifies a materialist ontology in which ultimate reality goes to what can be weighed and measured, and human consciousness is reduced to mere epiphenomenon.” 12
Nancey Murphy concurs, rejecting reductive materialism in favor of nonreductive physicalism. She accepts, within this viewpoint, ontological reductionism, the claim that we may consider complex living beings as products of their component parts. Nothing (like a soul, for example) needs to be added in order to achieve living status or consciousness. So no non-material entity (mind/soul) need be assumed. But consciousness and other mental states do exist and do have unique influences on us. “The human nervous system, operating in concert with the rest of the body in its environment, is the seat of consciousness (and also of human spiritual or religious capacities).” 13 Consciousness and religious awareness are considered as emergent properties, and have top-down causal influence on the body. 14 This concept may be contrasted with causal reductionism, an idea Murphy rejects, which is the view that the behavior of the most basic elements of a system determine the behavior of all higher-level entities. Thus, for the causal reductionist, causation must be entirely bottom-up, which is the claim of reductive materialists.
In psychological terminology, the key to comprehending Murphy’s position may lie within levels of analysis. We know that a specific experience may be analyzed in a variety of ways. A photograph may be interpreted as representing the person being pictured, or it may as reasonably be discussed in terms of the pixels of light that create the image. Each interpretation carries very different meaning, and the way the elements are organized adds another unique dimension of meaning. Gestalt psychologists have made us aware that particular organizations and configurations of elements can result in entirely different interpretations and experiences. The perception of continuity of images in a moving picture provide us with the experience of motion, even though no motion exists if we analyze the individual frames of a film. To understand causal influences on human behavior, then, we may need to allow the possibility of emergent, top-down causes that are neither reducible to the sums of their component parts nor to the laws that govern the activities of those parts. 15
CRITERIA FOR SELECTION
Faced with a number of models of human nature that boast strong advocates and compelling arguments, how are we to decide among them? For the Christian student of human nature, two key criteria should guide our reflection—consistency with biblical claims and consistency with available data.
I will not attempt to provide here anything approaching a comprehensive overview of biblical anthropology, 16 but wish only to highlight the fact that inconsistencies appear, resulting in difficulty in making strong claims for a coherent “biblical teaching.” Murphy notes that it is widely agreed that the Hebrew word that has been translated as “soul” (nephesh) refers not to a distinct disembodied entity, but to a unified living person. She concludes, rightly, that scriptural texts were not intended as texts on human anthropology or metaphysics. If it were so, she claims, their message on this point would have been much more clear. 17
In face of such controversy or lack of clarity, we may benefit from examining God’s extended revelation in nature. It is here that study in psychology, which seeks to explore directly the nature of human behavior and motivation, may provide crucial insights. If we are open to critically examining findings in the sciences, we may find that they provide some direction for our personal theorizing on human nature, though, as Jeeves and Murphy remind us, no amount of neuroscientific evidence can ever prove dualism false or physicalism true. We know that prominent scientists have examined much of the same evidence and have arrived at widely divergent conclusions. 18
It is recognized that scientific enquiry is inevitably a subjective enterprise, despite disciplinary ideals and conscientious efforts to exclude personal biases, beliefs, and agendas. Interpretation of evidence is always grounded within a particular worldview, from which we seek not only a coherent understanding of the facts before us but also a model or theory of how these facts fit within a larger framework. We are reluctant, often, to have our current viewpoint greatly disrupted, and this reluctance may cause us to distort, re-interpret, or ignore relevant data. Still, it is recognized that the same can be said about any human interpretive effort, whether it involves behavioral or biblical data. So we tread cautiously and humbly.
Research in psychology and related disciplines proceeds simultaneously at several levels, from the molecular to large-scale models of various aspects of behavior. One fact becomes clear in reviewing this evidence—the picture of human nature and behavior at every level is highly complex.
CONTRIBUTIONS FROM (NEURO)PSYCHOLOGY
Psychology has often been described as a discipline with a brief existence but a long history. Questions of the connection between mind and body were asked by the ancient Greeks. Empedocles, for example, advocated a cardiovascular theory, suggesting that mental functions resided in the heart. This seemed reasonable when one considered that feelings of excitement (say, at the thought of one’s beloved) appeared to cause one’s heart to beat more rapidly. Contemporaries like Alcmaeon suggested an encephalic theory, indicating that the brain was the center of thought, receiving sensations via pneuma within air channels in our sense organs and brain. A century later, Hippocrates, writing about his theory of the four humors, agreed that our mental life was centered in our brain: “. . . from the brain and the brain only arise our pleasures, joys, laughter and jests, as well as our sorrows, pain, grief, and tears . . . these things that we suffer all come from the brain when it is not healthy but becomes abnormally hot, cold, moist or dry.” 19 This view became dominant, with the result that speculations about mind-brain connections became common.
Despite the development of many such speculative theories (Descartes’ deduction regarding the pineal gland, etc.), little progress was made for many centuries in detailing these links. A famous story records that lexicographer Samuel Johnson suffered a stroke in the summer of 1783 that affected his ability to speak. His treatment involved blistering the outside of his throat (up to his ears), as well as his forehead and back. 20 Clearly, to that point in history, the mental activity involved in speech was not recognized to be closely linked to brain activity.
That would change only in the nineteenth century. In the 1860s, French physicians such as Boulliard and Paul Broca discovered evidence of localized speech production within the left frontal lobe (Broca’s area) after studying a patient named Leborgne and finding a lesion in this area of his brain. 21 This discovery among several patients with similar speech deficits opened the way to discoveries of cerebral dominance and localization of a number of specific psychological functions.
A story related in almost every introductory text in psychology concerned the unfortunate fate of railroad worker Phineas Gage in 1848. An explosion at a construction site drove a three-foot tamping rod upward through Gage’s left cheek, into his left temporal lobe, and out the top of his head. Remarkably, Gage survived the accident (he even remained conscious throughout) and recovered physically, but with notable psychological results. His personality seemed affected by the accident. He became irresponsible, his likes and dislikes changed, and his moral sense was altered. 22 Gage’s case seemed to indicate that not only were cognitive processes and events directly linked to brain function, but personality and social functioning might also be influenced. (Neurologist Antonio Damasio asked of this incident whether it would be fair to say that Gage’s “soul was diminished (by the blow), or that he’d lost his soul?” 23)
Neuropsychological advances, particularly magnetic resonance imaging (MRI) and positron emission tomography (PET) scanning techniques, have refined efforts to localize psychological and physical functions. For example, Michael Posner and colleagues have identified specific brain locations involved in visual attention and in deciphering the meaning of the text we read. 24 Similarly, Christopher Frith and colleagues have discovered different cortical regions associated with reflexive and controlled (volitional) shifts in visual attention. 25
Studies of face recognition provide fascinating and important insights. Occasional reports in the neurological literature indicate that some persons, after suffering a stroke, lose the ability to recognize faces, despite ongoing abilities to identify other objects. Rolls and colleagues have investigated face recognition ability by studying the brains of primates. 26 They have found specific columns of cells in the occipital lobe that respond only when the animal is shown a specific familiar face. In fact, some cells respond only when such a face is shown from a particular angle, whereas others respond when shown another perspective of the same face. Such very specific responding among cells associated with vision is recognized as the norm. Damage to specific cells, as follows a stroke, may result in very specific perceptual consequences. In human cases, reports indicate that patients may not identify a person’s face even though that person should be familiar, but may recognize in the same picture the emotion being expressed in that face. 27
Elsewhere, various memory systems are found to be affected by damage to different brain regions. For example, damage in the hippocampus or the amygdala appears to hinder our declarative memory (recall for names or events) whereas damage in phylogenetically older (midbrain) regions may create difficulties regarding procedural memory (memory for performing various tasks or skills). 28
We have seen increasing specificity in localizing a great variety of brain functions, particularly in the last couple of decades. These advances have been accompanied by a recognition that more complex processes (planning, problem solving) are not isolated in one brain region alone, but depend upon interactions of networks of cell units operating in diverse areas of the brain. Beginning to comprehend the mechanics of such highly complex brain activity depends in many ways on the level at which we choose to define any psychological function.
Furthermore, we find correlations not only between cognitive processes and localized brain activity. Emotional and social responses also appear to be intimately linked to specific brain function. Hare demonstrated different responses of patients diagnosed with psychopathic disorders relative to a group of control participants in a task asking them to read a list of emotion-laden words (such as “bloody,” “panic,” etc.). 29 In control participants, the ventromedial cortex and amygdala, regions associated with emotional responding, became active when reading these items whereas these areas remained relatively inactive in the brains of psychopathic patients. Such outcomes suggest that the brains of persons with psychopathy are abnormal in that they underutilize areas that normally process emotion and memory. Hare noted that these individuals are described as easily bored and craving of immediate self-gratification. They may be aware of society’s rules, but feel little or no guilt should they violate them.
Studies of aggressive responding indicate brain-based responding. Whereas it is clear that human aggression results from a complex array of cognitive and social influences, biological influences do exist. Harris and colleagues asked male and female participants to respond to questionnaire items measuring their self-reported tendencies to behave aggressively. 30 Items included “I have trouble controlling my temper” and “If somebody hits me, I hit back.” The researchers then measured participants’ level of testosterone, a hormone often linked to aggressive behavior. For both sexes, higher testosterone levels were correlated with higher levels of aggressive behavior. Albert and his co-researchers note that while higher testosterone levels do not inevitably result in high levels of aggression (again suggesting mediating social and other variables), aggression is notably increased in cases of tumors in the medial hypothalamus and septum, and greatly reduced following lesions in the amygdala. 31
The research examples noted above support the commonly held claim that much of our day-to-day activity is based on responses within our brains. That is to say, our brain affects our behavior. What is equally relevant to comprehending the intricate and inexorable link between mind/soul and brain is the more recent and possibly less intuitive discovery that our own behavior, experience, and mental life also affect the structure and functioning of our brain. The inescapable relationship between mind and brain is a reciprocal one. One facet cannot be affected without influencing the other.
In lower species, we learn that social success, such as gaining territory or mating opportunities, leads to production in the brain of certain hormones. Loss of social standing also has direct physical consequences. 32 In humans, gentle massage of preterm infants has been shown to result in the release of greater quantities of growth hormone by the pituitary gland, leading to faster physical growth compared to infants who do not experience this massage. 33
Our learning experiences change our brain chemistry and structure (even reading this article is creating temporary and possibly permanent changes in the reader’s brain!). Maguire and colleagues demonstrated such effects among taxi drivers in London, England. 34 It is well known that the hippocampus plays a vital role in spatial memory, and London cabbies are renowned for their detailed navigational memory. Using structural MRI scans, Maguire’s research team compared the hippocampi of a sample of London taxi drivers to those of control participants and found those regions in the brains of taxi drivers to be significantly enlarged. Moreover, the researchers found a correlation between hippocampus size and the amount of experience an individual had as a driver. The authors claimed these outcomes as evidence for local plasticity in the human brain as a result of experience.
Social experience may also influence the functioning of body and brain. A study of men whose wives had been diagnosed with terminal cancer found suppressed lymphocyte function, especially in the first months after the wife’s death. 35 Such findings indicate that psychological events, like profound grief or sadness, cannot be easily distinguished from the physical outcomes that accompany them.
This reciprocal influence between our psychological and physiological aspects has been recognized within psychology for some time as critical to our understanding of human behavior. Historical distinctions between physical activities or events and those deemed to be psychological or mental in nature have unfortunately been misleading, and yet these tend to carry on in everyday usage. Such distinctions originated understandably within various scientific circles as attempts to classify nature (often successful in a variety of disciplines—biological and chemical systems, for example) were applied to the blossoming study of human experience and behavior. Given limited knowledge about underlying causes of behavior or psychological symptoms, such classifications appeared to have some merit, even if they needed to be refined from time to time. It has come to be recognized, however, that neither experience nor disorder can ever be classified as wholly physical or wholly psychological in nature. As Antonio Damasio laments regarding the labels applied to diagnoses, “the distinction between diseases of ‘brain’ and ‘mind,’ between ‘neurological’ problems and ‘psychological’ problems or ‘psychiatric’ ones, is an unfortunate cultural inheritance that permeates society and medicine. It reflects a basic ignorance of the relation between brain and mind.” 36 Any human experience is always, inevitably, a product of both mind and body.
Kevin Corcoran notes that none of the currently popular views of human nature, whether dualist, physicalist, or some hybrid formulation, is completely satisfactory, free from “theological and ethical worries.” 37 Such a realization calls us to rather humble theorizing and to careful evaluation of our own personal theories and beliefs. We need to be open to accepting better data or better interpretations even if those may change our own stance.
With that said, I feel it is possible to weigh the evidence at hand and to take a position on issues of soul. Given that the biblical witness may be claimed to support either a dualist model or a materialist one, depending very much on one’s reading, and that a dualist view is not supported by neuroscientific evidence while a reductive materialist stance fails to explain those aspects of ourselves that seem most essentially human, it appears that a model such as nonreductive physicalism most reasonably conforms to our current understanding of our own nature. Such a view of the relationship between neuropsychological influences and our mental or spiritual experience allows for top-down causal influences and the sorts of reciprocity between body and mind that is so often in evidence in psychological research. It is possible to imagine those attributes and capacities often attributed to a distinct immaterial soul to be emergent characteristics of a physical system. This supports a holistic conception of humanity, to which insights from many disciplines may contribute. As Ric Machuga puts it, “we don’t have a soul, we are a soul [nephesh: living, breathing soul].” 38
In the ongoing quest to grasp our own nature, we will do well to remain open to learning the vocabulary, emphases, and insights gleaned from a variety of disciplinary perspectives. Each may reveal an important facet in our understanding.
- Nancey Murphy, Bodies and Souls, or Spirited Bodies? (Cambridge: Cambridge University Press, 2006).
- David G. Myers “Platonic Dualism or Hebraic Holism?” in The Human Puzzle: Psychological Research and Christian Belief (New York: Harper & Row, 1978), 73–90.
- Murphy, 4.
- Joel B. Green, lists some of the critical issues for which questions of human nature have important implications, ranging from questions of the uniqueness of humans relative to other species, to matters of free will, understanding “salvation,” what happens to us when we die, to the role and work of the church. See “Body and Soul, Mind and Brain: Critical Issues,” in In Search of the Soul, ed. J. B. Green, S. L. Palmer (Downer’s Grove, IL: InterVarsity Press, 2005).
- See, e.g., Keith Ward, In Defence of the Soul (Oxford: Oneworld, 1998).
- Green, “Body and Soul,” 13.
- Stewart Goetz, “Substance Dualism,” in In Search of the Soul, 33–60.
- William Hasker “On Behalf of Emergent Dualism,” in In Search of the Soul, 75–100.
- Francis Crick, The Astonishing Hypothesis: The Scientific Search for the Soul (New York: Simon & Schuster, 1994), 3.
- Donald M. MacKay, The Clockwork Image (Downer’s Grove, IL: InterVarsity Press, 1974).
- Donald M. MacKay, The Open Mind and Other Essays: A Scientist in God’s World (Leicester: Inter-Varsity Press, 1991), 23.
- Nancey Murphy, “Nonreductive Physicalism: Philosophical Issues,” in Whatever Happened to the Soul? Scientific and Theological Portraits of Human Nature, ed. Warren S. Brown, Nancey Murphy and H. Newton Malony (Minneapolis: Fortress Press, 1998), 131.
- Warren Brown has an interesting take on the capacities we may attribute to soul (consciousness, personal agency and responsibility, the ability to love and to receive love, to experience transcendence, to communicate with God, but also including our abilities in language, episodic memory, etc.). (See “Cognitive Contributions to Soul,” in Whatever Happened to the Soul, 99–125.) He claims that the concept of soul, based on biblical descriptions, characterizes our capacity for significant personal relationship. Ultimately, Brown argues, it is “God’s act of relating (to us) that engenders soul in each human being” (125).
- Malcolm Jeeves emphasizes the importance of levels of analysis in reviewing arguments regarding free will and determinism. He summarizes MacKay’s view that indeterminacy (and thereby free will) exists at the level of conscious experience, irrespective of any determinacy at the level of (cells in) the brain. He also cites Crutchfield’s argument that chaos may represent one mechanism allowing for free will in a world subject to deterministic laws of nature. See “Brain, Mind, and Behavior,” in Whatever Happened to the Soul?, 93–97.
- See, for example, Hans Walter Wolff, Anthropology of the Old Testament (London: SCM Press, 1974); and Gordon Zerbe, “Paul on the Human Being as a ‘Psychic Body’: Neither Dualist or Monist” (this volume) for a treatment of Pauline anthropology.
- See Murphy, Bodies and Souls, 16–21, for a summary of Old and New Testament examples of the use of “soul” in the KJV Bible. Some of these lend themselves to a dualist interpretation in which God rescues souls, even when bodies are resigned to the grave, whereas other passages describe souls as vulnerable to worldly harms. More recent translations have replaced some (not all) references to “soul” with “me” or “my life.”
- Murphy, “Nonreductive Physicalism,” 127.
- Hippocrates, On the Sacred Disease.
- David Myers and Malcolm Jeeves, “The Mind-Brain Connection,” in Psychology Through the Eyes of Faith (San Francisco: HarperCollins, 1987), 19.
- Morton Hunt, The Story of Psychology (New York: Anchor Books, 1993).
- Jeeves, “Brain, Mind, and Behavior,” 77–78.
- Antonio Damasio, Descartes’ Error: Emotion, Reason, and the Human Brain (New York: Grosset/Putnam, 1994), 118.
- E.g., M. I. Posner and C. D. Gilbert, “Attention and the Primary Visual Cortex,” Proceedings of the National Academy of Sciences 96 (1999): 2585–87; M. I. Posner and A. Pavese, “Anatomy of Word and Sentence Meaning,” Proceedings of the National Academy of Sciences 95 (1998): 899–905.
- E.g., A. C. Nobre et al., “Functional Localization of the System for Visuospatial Attention Using Positron Emission Tomography,” Brain 120 (1997): 515–33.
- E. Rolls et al., “Neuronal Responses Related to Visual Recognition,” Brain 105 (1982): 611–46.
- Antonio Damasio, “Mechanisms of Face Recognition,” in Handbook of Research on Face Processing, ed. A. W. Young and H. D. Ellis (New York: Elsevier, 1989).
- M. Mishkin and T. Appenzeller, “The Anatomy of Memory,” Scientific American 256, no.6 (1987): 62–71.
- Robert D. Hare, Without Conscience: The Disturbing World of the Psychopaths Among Us (New York: Pocket Books, 1993).
- J. A. Harris et al., “Salivary Testosterone and Self-Report Aggressive and Prosocial Personality Characteristics in Men and Women,” Aggressive Behavior 22 (1996): 321–31.
- D. J. Albert et al., “Aggression in Humans: What is its Biological Foundation?” Neuroscience and Biobehavioral Reviews 17 (1993): 405–25.
- E.g., J. Bradbury, “Social Opportunity Produces Brain Changes in Fish,” Public Library of Service: Biology 3 (11) (2005): e390.
- Tiffany Field, “Massage Therapy Facilitates Weight Gain in Preterm Infants,” Current Directions in Psychological Science 10 (2001): 51–54.
- E. A. Maguire et al., “Navigation-Related Structural Change in the Hippocampi of Taxi Drivers,” Proceedings of the National Academy of Sciences 97 (2000): 4398–4403.
- S. J. Schiefer et al., “Suppression of Lymphocyte Stimulation Following Bereavement,” Journal of the American Medical Association 250 (1983): 374–77.
- Damasio, Descartes’ Error, 118.
- Kevin Corcoran, “The Constitution View of Persons,” in In Search of the Soul.
- Ric Machuga, In Defense of the Soul, 16.