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What’s all this talk about controversy?

In school, students rarely learn to view disagreements among scientists as a natural part of the progress of science; most textbooks are written as if science is a set of truths to be memorized. Teachers, especially in America, are under enormous pressure to cover a large number of unrelated science topics each year to prepare their students for accountability tests, which generally measure students’ ability to recall facts. When breadth is emphasized over depth, there simply is not time to discuss how the scientific ideas came to be. There is barely time to help students grasp the meaning of the ideas themselves. On the rare occasions when students are exposed to historical ideas about science, those ideas tend to be dismissed with minimal discussion of why they were replaced, or why scientists held them in the first place. Students are left with the impression that scientists held some silly ideas in the past, but now they have it all figured out, and today’s scientific theories are true.

For folks who have never had the opportunity to learn how disagreements between scientists play a role in the progress of science, it can be confusing or frustrating to be told that scientists disagree about the meaning of a finding, or to find out that scientific advice they had taken to heart (eat margarine instead of butter) has been overthrown (avoid margarine—it’s bad for you). However, controversy within science has always been a normal part of the progress of science. Familiarity with past examples of clashes between scientists can help one better understand the science-in-the-making in the media today. The historical example of what came to be the foundational theory on which modern geology is built, though initially proposed by one scientist and rejected by nearly all of his contemporaries, provides insight into how and why revolutions in scientific thinking occur.

Scientific revolutions really happen

In 1912, Alfred Wegener formulated a hypothesis about continental drift. The basic idea of continental drift is that all of the earth’s landmasses were once joined together as a supercontinent, Pangaea, which later broke apart, leaving the continents gliding across the substratum. Wegener had several lines of evidence to support his continental drift hypothesis. The outlines of the continents look more or less as though they should fit together like pieces of a jigsaw. The distributions of living things, past and present, have striking similarities on different continents. There are similarities in rock formations on different continents. The distribution of climates was not the same a few hundred million years ago as it is today. Continental drift is an elegant hypothesis that can explain many puzzling observations. Yet many scientists gave it two thumbs down for nearly half a century.

The problem was that Wegener had no plausible mechanism for how continents could drift. It would take huge amounts of energy to move something as massive as a continent, no matter how slowly. How on earth could the continents be moving? Understanding mechanism is a big part of science, and scientists frown on “hand-waving” sorts of explanations, which is all Wegener could come up with based on the data available to him. Wegener himself recognized the gaps in his ideas and acknowledged them in his writing.

Ultimately, it was new data that drove the acceptance of continental drift. Three discoveries were pivotal. First, scientists discovered that the rocks on the ocean floor are much younger than the rocks that make up the continents. Second, they found a long chain of mountains, with active volcanoes along its middle and ancient volcanoes bordering them, that forms a continuous north-south seam in the middle of the Atlantic Ocean. Third, they discovered that there is a pattern of magnetic stripes with alternating polarity—some with their north pole facing north and some with their north pole facing south—along the ocean floor, parallel to the mountain chain beneath the Atlantic. Scientists already knew that, as it cools, molten rock laid down by volcanoes becomes magnetized according to the orientation of the earth’s magnetic field, and that the earth’s magnetic field has reversed itself several times throughout history. Therefore, the magnetic stripes on the ocean floor suggested that magnetized, solidified rock was pushed aside as new rock—which may have a different magnetic orientation depending on the orientation of the earth’s magnetic field at the time—was laid down by volcanic activity. These results are consistent with the idea that volcanic activity between adjacent continental plates caused Pangaea to break apart about 200 million years ago, forming the Atlantic Ocean. The continents on either side of the ocean are still being pushed apart as the Atlantic Ocean widens by a couple inches per year.

Wegener died during a research expedition to Greenland in 1930, about three decades before his ideas about continental drift revolutionized geology. In fact, much of the research that led to key findings about sea floor magnetic stripes and spreading had nothing to do with testing continental drift. The research was going on in the 1950s, during the Cold War, when the United States hoped that studying the sea floor would provide information that would allow it to disguise its own submarines and better detect the Soviet Union’s submarines. The nearly universal acceptance of continental drift resulted from the research of many scientists, working in different places on different projects. Eventually, as the pieces came together, the critique of Wegener’s ideas as “preposterous” no longer made sense. It was more preposterous to maintain that the arrangement of oceans and continents was immutable in the face of the overwhelming evidence in support of continental drift.

This account of continental drift leaves out work done since the 1960s. The later work has led to a more detailed theory known as plate tectonics, which subsumes continental drift and includes much more detail about the forces that drive the movements of the plates. Nonetheless, the lesson is clear. The clash of ideas is not a problem in science, but rather a normal part of scientific progress. In the face of new evidence, a crazy idea can become the foundation for work in a field. It may take time for the evidence to accumulate, especially if tools are not available to test a hypothesis directly, but in the end, it is the data that do the talking.

Disputes are not a sign of science gone wrong

Because people tend to think of science as a slow accretion of ideas, where discord has no place, the existence of disagreements between scientists has been used to attack the theory of evolution. For example, at one point, existing paleontological (fossil) evidence and molecular (genetic) evidence told different stories about from which animals whales had evolved. The genetic evidence suggested that whales and hippopotami were closely related and shared a common ancestor. According to the fossil evidence available at the time, whales and hippos were only distantly related. Antievolutionists pointed to this disagreement as a flaw in science and a reason for rejecting evolutionary theory. At the same time, the paleontologists and molecular biologists were far from satisfied by the lack of agreement between the two types of data. They came up with explanations for why each might be inaccurate. Paleontologists criticized the molecular evidence because genetics cannot be used to compare the many species that have gone extinct, only the living examples of related species (except in rare cases in which well-preserved DNA from extinct species is available). Molecular biologists criticized the fossil evidence as being insufficient because a small percentage of organisms become fossilized and of those that do and are unearthed, the limb bones may not be well preserved. However, there is a significant difference between the approach of the antievolutionists and the scientists. Unlike the antievolutionists, the scientists specified what would be convincing support for one position or the other. In addition, the scientists predicted that the controversy would be resolved when additional evidence, either molecular evidence or fossil evidence, came to light.

Paleontologists eventually discovered fossils of ancient whales that had hind limbs. The hind limbs contained ankle bones that were clearly similar to those of hippopotami and their close relatives. Therefore, the new fossil finds brought the fossil evidence and the genetic evidence on whale evolution into agreement. This example shows that pointing to discord between scientists as indicative of a weakness in science is misguided. Scientists point out discord themselves. They seek evidence that will help them resolve the discord. Discord arises because science is a work in progress. The scientific process is healthy when scientists are willing to reconsider their ideas in the light of new evidence. While it is completely sensible to draw attention to discord to highlight where more research is needed, it is not sensible to use discord between scientists as a reason to throw one’s hands in the air and give up on science.

Living organisms, earth processes, and the evolution of the universe are so complex that the existence of discord in science should not be puzzling. Even problems that seem straightforward, such as the relationship between estrogen levels and hot flashes, invariably turn out to be more complex when investigated thoroughly. Many women experience hot flashes—a feeling of intense heat often accompanied by flushing and sweating and sometimes followed by chills—as they approach and transition through menopause. Since estrogen levels decrease at menopause, and since estrogen supplements alleviate hot flashes, it is logical to assume that low estrogen levels trigger hot flashes. Some studies are consistent with this hypothesis, but others are not. While considered the hallmark of the menopausal transition, hot flashes can occur at other times of life and can affect both women and men. In addition, not all women experience hot flashes during menopause. Plus, some women who have low estrogen levels—for example, gymnasts or endurance athletes—do not experience hot flashes. These conflicting data have forced researchers to reconsider the role of estrogen in hot flashes. They hypothesize that hot flashes may not be triggered by low estrogen, but rather by estrogen levels that are in the process of declining. In other words, the cause may be the change in estrogen levels (dynamic) over time, not the absolute (static) level of estrogen at any point in time. Gathering the data to test the new hypothesis is trickier than gathering the data to test the original hypothesis. It requires following women over time to determine how their estrogen levels change and how the changes influence hot flashes. Long-term studies are expensive, time consuming, and challenging. In addition, other hormones and health and lifestyle factors likely play a role in who gets hot flashes. Since many experiments are needed to tease apart the complexities of an issue like the relationship between estrogen and hot flashes, it would be more surprising if conflicting ideas never arose in science and each new factoid was simply added on top of a pile of existing knowledge.

The media often misrepresents disputes between scientists

Disagreements between scientists are a normal part of the process of science, but the media often exaggerates, misrepresents, or oversimplifies these disputes to sensationalize the latest science news. This is especially common in headlines or brief sound bites. For example, there is new and still disputed evidence that moderate amounts of sun exposure may reduce a person’s chances of getting certain internal cancers like breast, endometrial, colon, and prostate cancer. It is not hard to imagine the headlines and sound bites proclaiming, “scientists now say sun is good for you!”

Let’s dissect this claim. On the surface, one could argue that it is accurate: Anything that reduces your risk of getting cancer is good. However, everyone knows that too much sun exposure can lead to skin cancer. So are scientists now disputing that? No. Is it possible that sun exposure could increase your risk of skin cancer, but decrease your risk of some internal cancers? Yes. Ultraviolet light from the sun can cause skin cancer by damaging DNA in skin cells, and this can ultimately cause cells to start multiplying out of control. Cancer is the result of the uncontrolled proliferation of cells. The proposed mechanism by which sun exposure might protect you from internal cancers is completely different. Exposure to the sun allows your body to synthesize vitamin D, and possibly other important compounds. Vitamin D, among other functions, may help prevent overproliferation of cells.

One obvious question is why sun exposure does not protect you from skin cancer if vitamin D can stop cells from proliferating out of control. It may be that the risk of bombarding the DNA in your skin cells with ultraviolet radiation from the sun outweighs the benefit of having a little extra vitamin D around. On the other hand, the sun’s UV rays do not penetrate all the way through your skin, so your internal organs could benefit from the protective effects of extra vitamin D without the negative effects of UV radiation on their DNA.

For at least three reasons, this debate is much more complex than the headline might lead one to believe. First, scientists are still disputing whether it is true that sun exposure can protect you from internal cancers. The evidence for the claim is epidemiological data—the comparison of disease rates in different populations—which is useful but has many weaknesses. People who live in places where they get more sun likely have other lifestyle differences, such as diet and exercise, than their cold weather-dwelling counterparts. Second, even if the claim holds up, there still remains a tradeoff between increasing your risk of skin cancer while decreasing your risk of internal cancers. Third, those who believe sun exposure may protect you from internal cancers are not encouraging people to fry themselves in the sun. The body tightly controls vitamin D synthesis, and maximal synthesis may come after as little as 10 minutes in the sun, depending on the latitude, time of year, and your skin tone. So synthesizing enough vitamin D might be feasible without a significant increase in the risk of skin cancer. At this time, the jury is still out.

This example reveals the weaknesses of relying on sound bites as news. The headline “scientists now say the sun is good for you,” might be used by some as a reason to lie out longer at the beach and/or to stop bothering to use sunscreen. On delving deeper into the evidence, it becomes clear these reactions would not be merited even if the relationship between sun exposure and reduced risk of internal cancers had been proven beyond a shadow of a doubt. Headlines and sound bites may give the impression that the disputing scientists share little common ground, when in fact, the dispute is often much more specific. In this example, the benefit of sun exposure in preventing internal cancers is under dispute; the risk of skin cancer from sun exposure is not. In the previous example, the scientists were not disputing that evolution occurred or that whales evolved from land animals; only what specific land animal is ancestral to whales was under dispute. Therefore, it is important to determine the extent of the disagreement between scientists before drawing conclusions about claims.

Another problem is what sociologist Christopher Toumey referred to as pseudosymmetry of scientific authority—the media sometimes presents controversy as if scientists are evenly divided between two points of view, when one of the points of view is held by a large majority of the scientific community. For example, until recently, the media often gave equal time and space to the arguments for and against humans as the cause of global climate change. Surveys of individual climate scientists have indicated that there is discord among scientists on the issue, but that the majority of scientists agree that humans are altering global climate. One analysis of a decade of research papers on global climate change found no papers that disputed human impacts on global climate. Also, all but one of the major scientific organizations in the United States whose members have expertise relevant to global climate change, more than a dozen organizations in all, have issued statements acknowledging that human activities are altering the earth’s climate. The American Association of Petroleum Geologists dissents. Therefore, there is a general consensus within the scientific community that humans are causing global climate change. While it is legitimate to explore the arguments against the consensus position on global climate change, it is misleading for the media to present the issue so as to give the impression that the scientific community is evenly divided on the matter.

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