Plan Of The Book

Scientists use two fundamental approaches for answering questions about nature, including human nature: nonexperimental methods involving pure observation and measurement, and experimental methods involving manipulation of natural processes. The key words in this sentence are "pure" and "manipulation" because observation and measurement are critical elements of both experimental and nonexperimental studies. In both types of studies, a comparative framework is usually important for interpreting results. In medical experiment s, for example, responses to a new treatment (experimental manipulation) in one group of people might be compared to responses in a control group that did not receive the treatment. In nonexperimental studies, health might be compared in two groups of people with different habits, such as smokers and nonsmokers.

Chapter 2 uses several studies of the health effects of vitamin C and similar compounds to illustrate both nonexperimental and experimental approaches in medical research. Experimental studies in medicine are called randomized, double-blind trials and are often considered the "gold standard" in such research. I introduce this approach by discussing two experiments to test the effects of large doses of v itamin C on the common cold. These examples illustrate some of the basic decisions that must be made in designing any experiment, such as what to use as a control treatment for comparison with the experimental treatment and how to measure responses to the treatment s.

Studies of the effects of vitamin C on the common cold demonstrate some of the pitfalls of designing effective experiment s. Although the hypotheses being tested in these experiment s were straightforward, the procedures were relatively simple, and the analyses of result s were uncomplicated, certain aspects of the experiments contributed to uncertain conclusions. I use these studies to illustrate experiments in medicine because their flaws are as informative as their strengths.

In Chapter 2 I also introduce purely observational st udies of the long-term effects of vitamin C and similar compounds on aging. One of the key studies asked whether elderly people in Basel, Sw itzerland, w ith high levels of vitamin C in the blood had better memory abilities than people with lower levels of vitamin C. In this example, different levels of vitamin C in the blood reflected dietary differences among subjects over long periods of time and possibly genetic differences affecting the metabolism of vitamin C. This and related examples illustrate the ambiguit ies that arise in interpreting results of nonexperimental studies, which are often more problematic than the pitfalls of interpreting experimental results. However, these examples also show that some kinds of questions don't lend themselves to an experimental approach. I revisit this theme in Chapter 8, which compares experimental and non-experimental studies of the effects of caffeine on blood pressure. Short-term effects were st udied with some well-designed experiment s, but understanding the consequences of a lifetime of coffee use required a purely observational approach.

I compare experimental and observational methods in several other chapters also. Chapter 3 describes the special challenges and rewards of using experiments to study animal behavior, in particular the ability of dogs to identify individual human beings by smell. Chapter 4 shows how observations in natural environments, laboratory experiments, and field experiments can be integrated to answer ecological questions. Chapter 5 returns to a topic in animal behavior, the spatial memory abilities of food-storing animals. These abilities were tested in a set of clever laboratory experiment s with nutcrackers, which complemented observations of the behavior of the birds in nature. In addition, comparative studies of the brains of various species provided insight about the neurological basis of spat ial memor y. These comparat ive studies were purely observational, like studies of the long-term effects of caffeine on blood pressure, but the context of the comparisons was much different. In the caffeine st udies, researchers were trying to understand differences in health among people who differed in coffee use and other habits; in the neurological studies related to spatial memory, researchers were trying to understand differences among species that have existed for thousands of generations. Nevertheless, the nonexperimental nature of both types of research produces similar challenges in drawing definitive conclusions.

In addit ion to illustrating how experiment s can be designed to test hypotheses in animal behavior, Chapter 3 has two other themes. First, it compares the use of evidence to answer scientific and legal questions. I return to this topic in Chapter 10. Second, Chapter 3 introduces a quantitative approach to evaluating the strength of evidence for or against an hypothesis. For example, we might hypothesize that a particular person committed a crime. Some evidence might include identification of the suspect by a trained police dog in a lineup or DNA of the suspect that matches DNA extracted from blood found at the crime scene. Under some circumstances, the strength of such evidence can be analyzed precisely enough to come up with a numerical estimate of the likelihood of guilt or innocence. But the results of these calculat ions can also be surprising. Chapter 3 describes the assumpt ions of this approach and discusses it s merits and limitations.

Chapter 4 tells t wo stories about frogs, one about trying to find the cause of high frequencies of leg deformities and one about trying to understand widespread population declines. I use the word "story" deliberately to emphasize how understanding these two problems developed through a sequence of observations and experiments, with results along the way leading to new hypotheses that were tested in further studies. One of my primary goals in

Chapter 4 is to show how the integration of results from naturalistic observations, laboratory experiments, and field experiments can be a powerful approach to rapid progress in biology. By contrast, reliance on a single method such as controlled laboratory experiment s can lead to dead ends. In addit ion to illustrating the complementary strengths of observational and experimental methods in ecology, the examples in Chapter 4 are important case st udies in conservation biology.

Chapter 5 continues exploring the interplay between experimental and observational approaches, but it has a more important objective. Several authors have pointed out the benefit s of developing and testing compet ing hypotheses for a phenomenon. For example, some species of animals store large amounts of food in widely dispersed locat ions in preparat ion for a season of food scarcity. How do animals find their stored food weeks or months later? Several possible mechanisms can be imagined, ranging from using smell to detect stored items (which may be invisible because they are buried) to remembering specific locations of the stored food. Chapter 5 discusses a set of simple but ingenious experiments to discriminate among these and other hypotheses. I use this concrete example to illuminate some fundamental philosophical principles about constructing and testing alternative hypotheses and about the roles of positive and negative evidence in science.

Chapters 6 and 7 don't focus as closely on observational and experimental methods as the other chapters, but they develop some ideas about causat ion that are important in interpreting studies in biology. I return to a medical example in Chapter 6: how the risk of getting cancer is influenced by genetic and environmental factors. This chapter was motivated by contrasting news accounts that appeared in July 2000 of a large Scandinavian study of cancer incidence in twins. One account highlighted the importance of genetic contributions to cancer risk; the other emphasized the importance of environmental factors. I was surprised that these stories, which appeared in major U.S. newspapers, could present such different interpretations of the same scientific study, so I read the original report in the New England Journal of Medicine. This led to the main theme of Chapter 6: the complex and diverse ways in which causal factors can interact to influence biological processes. I won't give away the conclusion about the roles of genetic and environmental factors in cancer here because the fascinating details are important for fully appreciating this conclusion.

This example was an important st imulus for me to write this book. It made me think about how science is presented in the press and whether it m ight be useful to elaborate on several recent news stories to show how science really works. I found that I could use different stories to illustrate various fundamental points about scientific methods, and eventually I had an outline for the book.

Chapter 7 cont inues to explore the complexit ies of causat ion, using different hypotheses about the causes of aging to illustrate a central theme—that biological phenomena have complementary causes at mult iple levels: biochemical, physiological, genet ic, developmental, environmental, and evolu tionary. This theme contrasts with that of Chapter 5, which shows the power of testing alternative, competing hypotheses to answer questions in biology. But the hypotheses considered in Chapter 5 are all attempts to explain the behavioral mechanisms by which birds and rodents find food that they store; that is, they are all explanations at the same level. In Chapter 7, I discuss mechanistic hypotheses about the biochemical and physiological causes of aging, as well as hypotheses about env ironmental factors that contribute to aging, genetic and developmental aspects of aging, and evolutionary reasons for aging. These kinds of hypotheses at different levels are not alternative explanations in the sense that if one is correct, the others must be false. Instead, all of these levels of causation must be considered for a full understanding of aging and of biological phenomena in general. Furthermore, progress in understanding at one level, such as mechan isms of aging, can stimulate progress in understanding at other levels, such as evolutionary reasons for aging.

Chapter 8 uses some studies of the effects of coffee on blood pressure and on cancer that nicely illustrate the tradeoffs bet ween experimental and purely observational research in medicine. This chapter also introduces the key role of replication in scientific research and describes a method that is commonly used to determine whether multiple studies of the same question give consistent answers. This quantitative approach to combining results from different studies is called meta-analysis. Many news stories about medical and nutritional research actually report the results of such statistical summaries of experimental or observational st udies of a topic, without ident ifying them as meta-analyses or explaining how the authors of the summaries reached their conclusions. Because of the widespread use of meta-analysis in medicine and nutrition, as well as in education, sociology, and other branches of the social sciences, I believe it is useful to understand the basic elements of this method.

Chapter 9 explores another basic conceptual tool of science, the use of quantitative models to help crystallize ideas and hypotheses. The primary example in this chapter is the possible effect s of global climate change on the occurrence of malaria in various parts of the world. Many people are intensely interested in predicting the likely consequences of global climate change during the next 50 to 100 years. These consequences include many changes in natural environments, as well as potential effects on human health. Because the global climate system is extremely complex, quantitative computer models have played a key role in developing predict ions about the extent and possible consequences of climate change. This is a topic for which it is tempting to defer to the experts who use these models. However, the predictions of the models have significant implications both for personal lifestyles and for nat ional and international policies about energy use and other env ironmental issues. Furthermore, these predict ions have been hotly contested by some scientists, which has promoted confusion about global climate change among politicians and members of the general public. Therefore, it's important to have a basic understanding of these models so that those without technical training can make intelligent judgment s about the associated controversies.

There are various approaches to modeling, and a major goal of Chapter 9 is to compare two very different kinds of models of the future distribution of malaria. These models have contrasting strengths and limitations. By giv ing you an opport unity to compare two such models, I hope to demystify the process of modeling by showing how the predictions of any model are linked to the assumpt ions used in mak ing it. My intention is not to contribute to your possible distrust of abstract models in general but to help you develop some tools for discerning the strongest points of particular models, as well as their most significant weaknesses. The process of comparing two different models should be an effective way to do this.

In Chapter 10 I elaborate on several threads that are initiated in the questions considered in earlier chapters. Most of the questions do not have final answers despite good and product ive research directed toward them, part ly because of their nature: human health (Chapters 2, 6, 7, and 8), animal behavior (Chapters 3 and 5), and global ecology (Chapters 4 and 9) are inherently complex because of the great diversity of factors that can influence them and the variability in responses to these factors that exist s in humans and other species. The lack of definitive answers to questions discussed in this book also reflects the fact that science is an ongoing process in which the most important sign of progress is often that result s of an experiment or observational study lead to a new set of questions. This is part of what makes science exciting and rewarding for scient ists, but it entails an important dilemma: how do we make the best practical and even ethical decisions based on incomplete scientific knowledge? Science impinges on many of the decisions that individuals and society in general must make. But there is often a fundamental tension bet ween the tentativeness of scient ific conclusions and the necessar y finality of some of our pract ical and ethical decisions.

Science is only one way of gain ing understanding of the world, albeit an especially powerful way. How does the scient ific approach compare to other approaches, such as art and religion? W hat are the strengths and limitations of these different approaches? W hat do they have in common? On a more practical level, how does the use of ev idence by scient ists and lawyers differ? I take up these kinds of questions in Chapter 10 to explore the scope of science in the larger context of the mult iple ways in which we, as humans, deal with the world.

Finally, in Chapter 10, I discuss the interplay between two key traits of scientists, curiosity and skepticism. In many ways these are contrasting human traits: consider the pure boundless curiosity of a young child and the unmitigated distrust of an old curmudgeon, for example. But the key to success as a scientist is often maintaining a delicate balance bet ween these two traits. In this book I hope to encourage both the curiosity and skepticism of readers who are not trained as scient ists. I believe this will help you read and interpret science news with greater understanding and pleasure and make more satisfying personal decisions about issues affected by development s in science based on k nowing more about how science works.

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