0. Studying Biology

0.3. Science Is a Way of Thinking


One of the most important things you can learn in a biology course is how to evaluate scientific claims. Long after this class is completed, you will be making decisions that involve biology, and they will be better, more informed decisions if you have acquired the skill to evaluate scientific claims for yourself. Because it is printed in the newspaper or cited on a website doesn’t make a scientific claim valid. Figure 0.5 illustrates the sorts of biology topics you encounter today in the news—and this is just a small sample. They are, all of them, important issues that will affect your own life. How do you reach informed opinions about them?



Figure 0.5. Biology in the news.


You do it by asking the question, “How do we know this?” In this text you will encounter a great deal of information and explanation, and will be asked to accept that what you are being taught is “true,” that it accurately reflects reality. In fact, what it accurately reflects is what we know about reality. Some of what we now know will be altered by future scientists as they learn more. How do they know they are right? Science is a way of thinking that demands to see the evidence, that challenges the validity of every claim. If you can learn to do this, to apply this skill in the future to personal decisions about biology as it impacts your life, you will have taken from this course a valuable lesson.


How Do We Know What We Know?

A useful way to learn how scientists think, how they constantly check and question what they know, is to look at real cases. What follows are four instances where biologists have come to a conclusion. These conclusions will be taught in this textbook, reflecting the world about us as best as science can determine. All four of these cases will be treated at length in later chapters—here they serve only to introduce the process of scientific questioning.

Does Cigarette Smoking Cause Lung Cancer? The American Cancer Society estimates that 562,340 Americans died of cancer in 2009. Fully one in four of the students using this textbook can be expected to die of it. Twenty-nine percent of these cancer victims, almost a third, die of lung cancer.

As you might imagine, something that kills so many of us has been the subject of much research. The first step biologists took was to ask a simple question: “Who gets lung cancer?” The answer came back loud and clear: Fully 87% of lung cancer deaths are cigarette smokers. Delving into this more closely, researchers looked to see if the incidence of lung cancer (that is, how many people contract it per 100,000 people) can be predicted by how many cigarettes a person smokes each day. As you can see in the graph in figure 0.6 (which is shown again on page 634), it can. The more cigarettes smoked, the higher the occurrence of lung cancer. Based on this study, and lots of others like it, examined in more detail on pages 230 and 524, biologists concluded that smoking cigarettes causes lung cancer.



Figure 0.6. Does smoking cause lung cancer?


Does Carbon Dioxide Cause Global Warming? Our world is getting warmer. Looking for the cause, atmospheric scientists soon began to suspect what might at first seem an unlikely culprit: carbon dioxide (CO2), a gas that is a minor component (0.03%) of the air we breathe. As you will learn in this course, burning coal and other fossil fuels releases CO2 into the atmosphere. Problems arise because CO2 traps heat. As the modern world industrializes, more and more CO2 is released. Does this lead to a hotter earth? To find out, researchers looked to see if the rise in global temperature reflected a rise in the atmosphere’s CO2. As you can see in the graph in figure 0.7 (which is shown again on page 796), it does. After these and other careful studies we will explore in detail on pages 796 and 812, scientists concluded that rising CO2 levels are indeed the cause of global warming.



Figure 0.7. Does carbon dioxide cause global warming?


Does Obesity Lead to Type 2 Diabetes? The United States is in the midst of an obesity epidemic. Over the last 16 years, the percentage of Americans who are obese has almost tripled, from 12% to over 34%. Coincidentally (or is it a coincidence?), the number of Americans suffering from type 2 diabetes (a disorder in which the body loses its ability to regulate glucose levels in the blood, often leading to blindness and amputation of limbs) has more than tripled over the same 16-year period, from 7 million to more than 23 million (that’s one in every 14 Americans!).

What is going on here? When researchers compared obesity levels with type 2 diabetes levels, they found a marked correlation, clearly visible in the graph in figure 0.8 (which is shown again on page 629). Investigating more closely, the researchers found that an estimated 80% of people who develop type 2 diabetes are obese. Detailed investigations described on page 629 have now confirmed the relationship that these early studies hinted at: Overeating triggers changes in the body that lead to type 2 diabetes.



Figure 0.8. Does obesity lead to type 2 diabetes?


What Causes the Ozone Hole? Twenty-five years ago, atmospheric scientists first reported a loss of UV-absorbing ozone (O3) gas high in the atmosphere over Antarctica. Trying to understand the reason for this “ozone hole,” researchers began to suspect chlorofluorocarbons, or CFCs. CFCs are supposedly inert chemicals that are widely used as heat exchangers in air conditioners. However, further studies, detailed on pages 22-23, indicated that CFCs are not inert after all—in the intense cold temperatures high over Antarctica, they cause O3 to be converted to O2. Scientists concluded that CFCs were indeed causing the ozone hole over Antarctica. As you can see in the graph in figure 0.9, the size of the ozone hole soon stopped expanding after CFC production was restricted.



Figure 0.9. What causes the ozone hole?


Looking at the Evidence

One thing these four cases have in common is that in each, scientists reached their conclusion not by applying established rules but rather by looking in detail at what was going on and then testing possible explanations. In short, they gathered data and analyzed it. If you are going to think independently about scientific issues in the future, then you will need to learn how to analyze data and understand what it is telling you. In each case above, the data is presented in the form of a graph. Said simply, you will need to learn to read a graph.

Key Learning Outcome 0.3. Scientists investigate by gathering data and analyzing it to form possible explanations they can test.