The biological domain concerns those factors within the body that influence or ar influenced by personalit . This domain is not any more fundamental than the other domains, nor is knowledge about this domain any closer to the "truth" about personality than knowledge in other domains. This domain simply represents one perspective on the nature and consequences of personality.
There is a long history of speculation and theorizing about the relation between the body and the mind. Some of this speculation has led to dead ends. For example, less than a century ago, people believed that the bumps on a person' s head revealed his or her personality . This so-called science of phrenology has been discredited and abandoned. Nevertheless, many modern personality psychologists believe that differences between people in other bodily systems (such as activity in the brain and peripheral nervous system) are related to their personalities. People who like a lot of stimulation and thrills in their lives, for example, might differ from those who don' t in terms of certain blood chemicals that influence nerve transmis sion. Or shy people might have a more reactive sympathetic nervous system compared to socially confident people
The biological domain refers to those physical elements and biological systems within our bodies that influence or are n-fluenced by our behaviors, thoughts, an feelings. For example, one type of physical element within our bodies that may influ ence our personalities is our genes. Our genetic makeup determines whether our hair is curly or straight, whether our eyes are blue or brown, and whether we have large, heavy bones or a slight build. It also appears that our genetic makeup influence how active we are, whether we are hot-tempered and disagreeable, and whether we like to be with others or prefer solitude. Understanding if and how genetics contribute to personality falls squarely within the biological domain. This is our subject in Chapter 6.
Another area in which biology and personality intersect is in the physiological systems, such as the brain or peripheral nervous system, where subtle differences between people might contribute to personality dif ferences. For example, some people might have more activity in the right half than in the left half of their brains. Based on recent evidence, we know that such an imbalance of activation between the brain hemispheres is associated with a tendency to experience distress and other negative emotions more strongly. Here, physical dif ferences between persons are associated with differences in emotional style. Because such differences represent enduring and stable ways that people dif fer from one another, and otherwise conform to our definition of personality laid out i Chapter 1, these physiological features represent aspects of personality . We'll cover physiological approaches to personality in Chapter 7.
In some areas of research a physiological response is viewed as a correlate or indicator of a trait. It is not viewed as a causal mechanism that serves as the physiological basis of the trait in question. Rather , the physiological response is considered a biological correlate of a particular trait.
The literature in personality psychology contains many examples of physiological measures that are considered to be correlates of personality. The finding that sh children show elevated heart rates when in the presence of strangers, compared to nonshy children, is one such example (Kagan & Snidman, 1991). Would eliminating the heart rate reactivity make the shy child less shy? Probably not. This is because the physiological response is a correlate of the traits in question, rather than an underlying substrate that produces or contributes to the personality trait.
This is not to say that studying physiological correlates of personality is a worthless endeavor. On the contrary, physiological measures often reveal important consequences of personality . For example, the high cardiovascular reactivity of Type A persons may have serious consequences in terms of developing heart disease. For this reason identifying physiological measures that are correlates of personality is also a scientifically useful and im portant task.
On the other hand, there are several modern theories of personality in which underlying physiolo gy plays a more central role in generating or forming the substrate of specific personality di ferences. In Chapter 7 we will consider several of these theories in detail. Each shares the notion that specific personalit traits are based on underlying physiological dif ferences. Each theory also assumes that if the underlying physiological substrate is altered, the behavior pattern associated with the trait will be altered as well.
The third biological approach we will cover is based on Charles Darwin's theory of evolution. Support for evolution comes mainly from fossil evidence that species developed physical adaptations to their environment. Adaptations that helped members of the species to survive and reproduce were passed on as evolved characteristics. For example, primates who could walk upright could colonize open field and their hands were freed for using tools. Evidence for the evolution of such physical characteristics is solid. Psychologists are now considering evidence for the evolution of psychological characteristics. They are taking the principles of evolution, such as natural selection, and applying them to an analysis of psychological traits. For example, natural selection may have operated on our ancestors to select for group cooperation; those early humans who were able to cooperate and work in groups were more likely to survive and reproduce, and those who preferred not to cooperate were less likely to become an ancestor . Consequently, the desire to be part of a group may be an evolved psychological characteristic that is present in today's population of humans. Evolutionary perspectives on personality are discussed in Chapter 8.
The biological domain dif fers from all the other domains in that it is concerned with those factors within the person that are based upon physical aspects of bodily functioning. The French philosopher Merleau-Ponty stated that the body is our "entry into the world." By this he meant that we are, firs and foremost, physical creatures dependent on our bodies for all information about, and interactions with, the world around us. The world we come to know and experience is thus influenced by the functionin and status of our physical bodies. For example, a person with an over-active sympathetic nervous system might experience his or her world as a place that is anxiety producing and might be seen by others as being a person who is "on edge" and prone to nervousness.
In this part of the book we describe some of the major ideas and findings from the domain of biolog as it applies to personality . As you read, it is important to keep in mind that biology is not destiny . Rather, the best way to think about the biological domain, as well as any of the other domains, is that it refers to one set of factors that influence or are re lated to personality . Personality is best thought of as multiply determined, as the collection of influ ences from all six of the broad domains of knowledge to be considered in this book.
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