HUMAN NATURE

Many ethical judgments make appeals to human nature either as their foundation or as their standard. In the strongest case ethics is argued to be based on human nature; in other instances actions are proscribed if they fail to respect human nature or are recommended because they are said to be in harmony with human nature. Human nature is also an object of scientific investigation, raising questions related to both process and product: whether scientific investigation is undertaken in ways that respect human nature and whether the results of such investigations can contribute to the understanding of human nature in an ethically relevant sense. After a brief review of theories of human nature, the focus in this entry will be on the final question: the extent to which scientific knowledge of human beings can contribute to understanding or assessing these theories, especially in their role as foundations for ethics.

Theories of Human Nature in History

According to Leslie Stevenson (2004), theories of human nature entail theories about the world, human beings, what might be wrong with human beings, and how anything that is wrong might be corrected. Even those who deny any essential human nature in favor of a historical or cultural construction of human nature have views about what kinds of things human beings are and their place in the world. However, with regard to explicit theories of human nature, premodern theories generally viewed humans as properly subordinate to a larger order so that even though people on occasion rebel against that order (by means of what the Greeks calls hubris and the Bible calls sin), they are called upon to learn to control such rebellion by means of ethical or religious practices. By contrast, modern theories tend to see human beings as unjustly limited by the larger order and thus encouraged to overcome those limitations, often by means of science or technology.

More specifically, for Plato, in a famous analogy from the Republic (p. 437b ff.), the human soul is presented as being composed of three parts: appetite, reason, and spiritedness. Lack of order results whenever appetite or spiritedness predominates and steps outside the guidance provided by reason. In a similar manner, for Aristotle in Nicomachean Ethics (vol. I, p. v), human lives can be oriented toward pleasure, politics, or knowledge, but the perfection of human nature resides with rationality in both practice and theory. Thomas Aquinas (1224–1274) further develops this perspective by arguing that the lawful order of nature is manifest in human nature (in a form he terms natural law) in aspirations to life, affective sociability, and the rational pursuit of both politics and science. Although the Jewish, Christian, and Islamic views of human nature seek in some measure to subordinate rationality to faith in revelation, that faith, like reason, ultimately places boundaries on appetitive, political, and even scientific activities. Structurally similar views can be found in the Asian religious and philosophical traditions associated with Hinduism and Buddhism.

More typically modern theories such as those of Thomas Hobbes (1588–1679) and John Locke (1632–1704), even when they offer a materialist and mechanistic analysis of the workings of human nature, argue that humans are improperly constrained by the state of nature. In Hobbes's frequently cited description, the state of nature is one in which human life is "solitary, poor, nasty, brutish, and short" (Leviathan, vol. I, p. 13), a condition from which human beings justly seek any means of escape. This notion that people are unjustly constrained by the human condition is repeated and developed in philosophies as diverse as those of Jean-Jacques Rousseau (1712–1778), Immanuel Kant (1724–1804), Georg Hegel (1770–1831), and Karl Marx (1818–1883). According to Rousseau, for instance, "Man is born free, but everywhere is in chains" (Social Contract, vol. I, p. 1). The psychological theory of Sigmund Freud, with its distinction between id, ego, and superego, reverses Plato's theory by suggesting the primacy of id or appetite over both individual self (ego) and social restraint (superego).

Three Basic Approaches to Human Nature

What can science contribute to the assessment or criticism of these diverse theories of human nature? One scientific debate concerns the relative influences of nature and nurture in human affairs. Another focuses on degrees of rationality or nonrationality in human decision and action. Among the most fundamental questions is that concerning whether there is something—a rational or transrational mind or soul—that cannot be accounted for by the same material causes that govern all other things in the natural world.

Materialism (or physicalism) is the position that the physical world is self-contained or closed so that the physical world can be explained only through physical causes and effects. In considering human nature, a materialist would say that human beings must be explained as purely material mechanisms, as physical bodies governed exclusively by physical causes. Consequently, the human mind should be understood as an activity of the physical brain. All the thinking, feeling, and willing of the conscious self must be determined totally by the body, particularly the brain and nervous system.

Against such a materialist view of human nature a dualist would argue that mind is not fully reducible to body, that the mind can act as an immaterial cause on the material brain. An interactionist dualist would agree that the mind depends on the brain as its necessary but not sufficient condition. Thus, if some part of the brain is damaged or ceases to function normally, this can interfere with mental activity. Still, as long as the mind is supported by normal brain activity, the mind can exert its independent power over the brain. When people act through conscious thinking and willing, they use their immaterial minds to control their material brains. A religious believer might go further and claim that the immaterial mind was created by an immaterial God, and thus the mind or soul is supernatural. This supernatural character of the soul could render it immortal so that the human soul could survive the death of the human body.

There are, then, at least three fundamentally distinct views of human nature that are based on three views of the relationship between mind and body. The materialist believes that the mind has no immaterial power to act on the body. The interactionist believes that the immaterial mind interacts with a material body. The supernaturalist believes that the immaterial mind is supernatural and immortal. Each of these views implies more general perspectives on human beings and their place in nature.

Traditional Arguments for Interactionism

These conflicting views run throughout the history of natural science from Socrates to the present. In Plato's Phaedo (pp. 96a–100a) Socrates (470–399 b.c.e.) talks with his friends while awaiting execution. He recounts that as a young man he thought that a scientific investigation of nature would explain the causes of everything. He hoped to explain the physical causes of all things coming into being and passing away, including the causes of animal life and the causes of human thinking in the brain. He became frustrated when he found that a complete science of nature as governed by physical causes was beyond his grasp. To explain the world, Socrates insists, it is necessary to understand both physical causes and mental causes. For example, to explain why Socrates is sitting here awaiting his execution, one might describe the physical mechanisms in his body—the bones, muscles, ligaments, and so on—that control his movement. However, although these physical causes are necessary in explaining why he is sitting here, they are not sufficient. It is also necessary to explain how Socrates made up his mind to accept his punishment because this mental decision controls his physical body.

Socrates appeals to a person's ordinary experience of making up his or her mind and then freely choosing to act according to that conscious mental decision; this leads people to think that the mind has a power to act that changes the physical causes of the body. Holding oneself and others morally and legally responsible for their conduct assumes that freedom of thought and choice. People do not hold nonhuman animals or human children morally responsible for their behavior because it is assumed that they lack the moral freedom that is attained only by the development of rational choice in normal human adults through learning and habituation. If human conduct were fully determined by physical causes in the body, it would be impossible to hold people morally or legally responsible for their conduct.

From ancient Greece to the present this kind of Socratic thinking has led many scientists, philosophers, and theologians to conclude that human nature is characterized by a complex interaction of mind and body, mental causes and physical causes. The human mind acts upon the human body, or the mind exerts an immaterial power that is not reducible to the material causes of the body.

Modern Arguments for Materialism

Socrates was responding to a materialist or physicalist tendency that would become a strong tradition in Western science. That materialist tradition gained great power during the scientific revolution of the sixteenth and seventeenth centuries. Proponents of the new science saw the universe as a mechanism that could be explained by mechanical laws working through purely physical causes. It seemed that much of human nature could be explained similarly without invoking an immaterial soul.

Hobbes saw nature as matter in motion governed by laws of motion such as those discovered by Galileo (1564–1642). Animal life, then, including human life, is "but a motion of limbs." "For what is the heart, but a spring; and the nerves, but so many strings; and the joints, but so many wheels, giving motion to the whole body" (Leviathan, Introduction). Animal motion is driven mechanically by selfish passions that goad animals to seek pleasure and avoid pain. Although human beings are moved by some of the same selfish passions, humans are unique in their capacity for reason and speech. However, even this uniquely human intellectual activity can be understood mechanistically as the computational manipulation of informational symbols (Leviathan, vol. I, p. 5). The soul or mind cannot be immaterial. It must be the activity of the material body. This must be so if one accepts the claim of natural science that everything in the universe is matter in motion. Because of his materialism Hobbes was denounced by religious and political leaders as a morally corrupting teacher of hedonism, egoism, and atheism.

Hobbes's materialist science of the soul seemed to be confirmed by Thomas Willis's (1621–1675) studies of the brain. Working in England at the same time as Hobbes, Willis compared the anatomy of the human brain with that of other animal brains and combined experiments on brains with medical observations of brain-damaged patients to develop what he called "neurology." He reached five broad conclusions. First, all mental experience arises from the motion of "animal spirits" undergoing chemical changes in the brain. Second, different parts of the brain have different functions. Third, the human brain resembles other animal brains, particularly those of monkeys and apes. Fourth, this science of neurology could be used by medical doctors to cure diseases of the brain through the use of drugs that would alter the chemistry of the brain. Fifth, all this supports the general view of the "mechanical philosophy" of the seventeenth century that the human body and brain are both machines explainable by mechanical laws.

Although Willis was mistaken about many details, his broad conclusions are supported by modern neuroscience. What Willis called animal spirits can be understood as electrical and chemical signaling between neurons. Willis's observation that the brain has specialized functions has been elaborated by studies of the ways neurons are organized into modular networks with distinct functions. Willis's claim that the human brain resembles the brains of other animals can be explained by evolutionary biology. His hope that drugs could cure the diseases of the soul seems to have been fulfilled by modern psychopharmacology in its use of drugs to treat mental disorders and enhance mental function. Finally, Willis's mechanistic account of the mind has been elaborated with computer models of the mind as an information-processing system.

It may appear, then, that the science of the human brain initiated by Willis proves Hobbes's materialist view of the soul. However, Willis was not a strict materialist because he believed that his science showed the existence of two souls. The "sensitive soul" found in all animals was purely material and therefore vulnerable to physical diseases. In contrast, the "rational soul" found only in humans was immaterial and immortal, although it depended on the sensitive soul. Thus, Willis's account of human nature was interactionist in that he thought the material brain and the immaterial soul mutually influence each other. He was also a supernaturalist in that he thought the immaterial soul was created by God to be immortal.

In the early twenty-first century some scientists, such as James Watson (2003), Edward O. Wilson (1998), and Steven Pinker (2002), argue that natural science sustains a purely materialist view of human nature and refutes any belief in the human soul as immaterial or immortal. Those scientists dismiss belief in an immaterial soul as an unscientific superstition. However, other scientists, such as Wilder Penfield (1978) and John Eccles (1994), defend Willis's interactionist view of the mind as an immaterial cause that can act on the brain. Eccles, a Nobel Prize–winning neuroscientist, has argued that modern neuroscience is compatible with belief in the self-conscious mind as an immaterial power for thinking and choosing.

Ethical Implications

What difference do these debates over the science of mind-brain interaction make for an understanding of human nature and morality? Those who argue for an immaterial soul agree with Socrates that the capacity of the mind to act outside the laws of physical nature is necessary for moral freedom. They warn against scientific materialism as a denial of free will that would make it impossible to hold people morally responsible for their conduct. They also warn that a materialistic view of human nature would promote a Hobbesian hedonism in which people would see themselves as animals moved by selfish passions with no spiritual capacity for rising above their material interests. To explain the soul as merely biochemical activity in the brain would seem to deprive human life of any unique moral dignity. Moreover, if scientific materialism teaches that human nature has only limited dignity above the rest of nature and if the ultimate end of modern science is the conquest of nature, people may be tempted to use the technological power of science to alter human nature itself in ways that would be dehumanizing.

The history of eugenics illustrates the potentially corrupting effects of a materialist view of human nature. The Judeo-Christian view of human beings as having been created in God's image with immortal souls has supported the moral principle of the special sanctity of human life. However, by the end of the nineteenth century modern science, particularly Darwinian science, had persuaded many people that human beings are merely highly evolved animals and that they do not have immaterial or supernatural souls that set them above the rest of animal nature.

If human beings are products of an evolutionary process governed by survival of the fittest, it seemed that reproductive fitness would be the only moral value coming from nature. Proponents of eugenics argued that human beings should be bred just as other animals are to improve the genetic quality of the species. As a result many state governments in the United States passed laws that forced individuals regarded as genetically inferior to be sterilized so that they could not reproduce. In Nazi Germany, Adolf Hitler (1889–1945) used policies of eugenics, euthanasia, and genocide to eliminate people whom he identified as belonging to inferior races. Some historians, such as Richard Weikart (2004), have explained the horrors of eugenics and Nazism as having been caused partly by the influence of Darwinian materialism in devaluing human life.

Other philosophers such as Peter Singer (2001) have argued that because religious belief in the sanctity of human life has been refuted by scientific materialism, people may be morally justified in euthanizing infants born with severe deformities. Some posthumanist or transhumanist proponents of biotechnology see no moral limit on the power to use science to redesign human beings, perhaps even to the point of abolishing human nature itself. All this seems to confirm the fears of many people that modern science, insofar as it promotes a materialist view of human nature, subverts traditional morality.

At the same time some scientific reasoning about the human mind may support traditional morality by showing how it is rooted in the brain. In The Descent of Man (1871) Charles Darwin (1809–1882) argued that a natural moral sense was implanted in human nature by evolutionary history. As naturally social animals, human beings evolved to have a natural sense of right and wrong that would support social cooperation on the basis of ties of kinship and reciprocity. To reinforce this cooperative behavior they were endowed with emotional propensities to moral emotions such as love, guilt, and indignation and also were endowed with the intellectual capacity to formulate social norms of cooperation rooted in those moral emotions.

Some neuroscientists have found that moral experience depends on the moral emotions sustained by the emotional control centers of the brain and on the moral reasoning carried out in the prefrontal cortex of the brain. If these parts of the brain are not functioning normally, people cannot act as moral beings. For example, psychopathic criminals apparently have an abnormality in their brain circuitry that prevents them from feeling the moral emotions that support the moral conduct of normal human beings. Such scientific research suggests that morality is part of the biological nature of human beings.

LARRY ARNHART

SEE ALSO Christian Perspectives: Historical Tradition;Dignity;Enlightenment Social Theory;Hobbes, Thomas;Humanization and Dehumanization;Hume, David;Natural Law;Posthumanism.

BIBLIOGRAPHY

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Stevenson, Leslie Forster, and David L. Haberman. (2004). Ten Theories of Human Nature, 4th edition. New York: Oxford University Press. Includes three ancient religious views (Confucian, Hindu, biblical), five philosophical views (Plato, Kant, Marx, Freud, and Sartre), and two scientific views (behavioral and evolutionary psychology).

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