The Idea of Human Nature, Part 1: Leslie Stevenson

In his Ten Theories of Human Nature, Leslie Stevenson argues that theories of human nature require 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 beings human beings are and their place in the world. 

Premodern theories of human nature generally viewed humans as properly subordinated to a larger order so that even though people might rebel against that order, 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 of things, and thus they are encouraged to overcome those limitations, often by means of science or technology. 

For Plato, in a famous analogy from the Republic, the human soul is presented as composed of three parts: appetite, spiritedness, and reason. Disorder arises whenever appetite or spiritedness departs from the rule of reason. Similarly, for Aristotle in the Nicomachean Ethics, human lives can be directed to pleasure, politics, or knowledge, but the perfection of human nature comes from the rule of reason--practical reasoning or theoretical reasoning. Thomas Aquinas further develops this perspective by arguing that the lawful order of nature is manifest in human nature as natural inclinations to life, affective sociability, and the rational pursuit of politics and philosophy. Although the Jewish, Christian, and Islamic views of human nature seek in some measure to subordinate reason to faith in revelation, that faith, like reason, ultimately places boundaries on appetitive, political, and even scientific activities. Similar views can be found in the Asian religious and philosophical traditions associated with Hinduism and Buddhism. 

Typically modern theories of human nature such as those of Thomas Hobbes and John Locke, 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 famous description, the state of nature is one in which human life is "solitary, poor, nasty, brutish, and short," a condition from which human beings must escape to enjoy a civilized life. 

What can science contribute to the assessment of these diverse theories of human nature? One scientific debate concerns the relative influences of nature and nurture in human affairs. Another concerns the degrees of rationality or irrationality in human decisions and actions. Among the most fundamental questions is whether there is something--a rational or transrational mind or soul--that cannot be accounted for by the material causes that govern all other beings 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. So, 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, although orthodox Christianity teaches that immortality requires the resurrection of the 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.