WHY SCIENTISTS CAN NEVER PROVE THAT BIOTECH CROPS ARE SAFE|
How Does Science Work?
Dr. Robert K. D. Peterson
Agricultural & Biological Risk Assessment
Montana State University
Many people who object to biotech crops argue that the crops should not be allowed to grow in the environment until science proves that they are safe. Others who support biotech crops argue that science has proven that they are indeed safe. However, the concept of proof has no place in science. Many people who do not actively practice science do not understand that science is structured so that scientists can never prove anything.
To understand why science cannot prove anything, we need to define and discuss two terms, “Science Literacy” and “Scientific Literacy.” “Science literacy” is knowledge about science facts. Facts such as the Earth orbits the sun, photosynthesis takes place in plant cells, and atoms are made of electrons, protons, and neutrons are all examples of science literacy. But science literacy is very different from scientific literacy. “Scientific literacy” is knowledge of science as a process for understanding the physical world.
So, what do we mean by “science as a process?” In other words, how does science work? Science and scientists utilize the scientific method, a standard, rigorous, and step-wise process to understand the world. After an idea or observation, scientists pose a hypothesis, which is a tentative explanation or assumption about some particular aspect of nature. To be valid, the hypothesis must be testable, and, more importantly, it must be refutable. When the hypothesis is tested, it is either supported or refuted. If the hypothesis is refuted, then an alternative hypothesis is posed and the process continues. If a hypothesis is not refutable (or falsifiable), it does not meet the minimum requirements of the scientific method. For example, a hypothesis that God created the earth cannot be refuted, and therefore it cannot be evaluated using the scientific method.
Hypotheses and theories can never be proven true using the scientific method. Therefore, science advances only through disproof. This is a critical and often misunderstood point. To be scientific, theories can never be proven true, but all theories must be refutable. Therefore, all theories, and by extension all of science, are tentative.
As an example, let’s use a science fact that is known to most adults: the existence of electrons. We know that electrons exist, but here’s the rub: Science can never prove that electrons exist. Hypotheses about the existence of electrons have been supported after countless tests using the scientific method. In other words, they have not been refuted. Knowledge of the precise nature of electrons will always be undergoing refinement, but the weight of scientific evidence clearly supports the existence of electrons.
|Scientific Proof and the Debate Between Evolution and Creationism
Understanding how science works also is critical to understanding the seemingly never-ending debate between those who support evolution and those who support creationism. The debate typically devolves (no pun intended!) into the argument by creationists that scientists cannot prove that evolution has occurred; therefore, their hypotheses of creationism are equally valid. Hypotheses regarding numerous aspects of evolution have been posed and tested. As testing has winnowed out incorrect ones, our understanding has become ever more clear. As with electrons, knowledge of the precise nature of evolution will undergo constant refinement, but the total current weight of scientific evidence supports the existence of evolution. As scientists, we do not arrive at that conclusion out of capriciousness or because of a “leap of faith,” but rather because of the systematic process for understanding physical reality called the scientific method. In fact, anyone who supports evolution because of faith or belief is not using scientific rationality.
Several arguments posed by creationists do constitute hypotheses and therefore are falsifiable. The hypothesis that the Earth is no more than 10,000 years old has been proposed numerous times, but refuted in many ways. Conversely, alternative hypotheses that the Earth is much older have been repeatedly supported. Indeed, today the weight of evidence overwhelmingly suggests that the Earth is billions of years old. Unfortunately, many other arguments posed by creationists are not falsifiable and therefore cannot be addressed using scientific inquiry. How can we falsify the hypothesis that God or an Intelligent Designer created the major forms of life on Earth? Creationist theories that cannot be refuted represent a particular world view, but they are not science. These theories can be taught in schools as philosophy or religion, but they must not be taught as science, unless the instructor uses them to demonstrate to the class what is and what is not science.
How about another example? This time we’ll use an example from plant biology and agriculture. A scientist states a hypothesis that adding nitrogen to the soil will result in increased grain production in corn (maize) plants. The scientist tests the hypothesis in a carefully controlled experiment. Her hypothesis is that nitrogen will increase grain production, and because the hypothesis must be subject to refutation, her alternative hypothesis is that nitrogen will not increase grain production. The experiment reveals that nitrogen does indeed increase grain production. Therefore, her initial hypothesis (also known as a null hypothesis) is supported. If the experiment had not resulted in increased grain production, the initial hypothesis would have been refuted and the alternative hypothesis would have been supported. The scientist can never prove that adding nitrogen to soil increases grain production, but if the hypothesis is supported time and time again, the weight-of-evidence convinces us that the relationship between nitrogen and increased grain production exists and is predictable.
As the instructor, hold a rock three to four feet above the floor. Ask the students what will happen if you let go of the rock. Hopefully, they will say that the rock will drop to the floor! Then, ask the students to prove that the rock will fall to the floor before you let go. They invariably will argue that rocks always fall to the ground when released, so when you release the rock it also will fall. But their statement does not prove that the rock will fall (or prove the existence of gravity). Their statement is based on countless observations of objects falling to the ground when dropped from above the ground. They are basing their statement not on proof, but on an overwhelming weight-of-evidence of what has happened to objects after they were released. Scientific explanations of falling objects started with a hypothesis that the rock would fall to the ground when released. Remember, to be a valid hypothesis, the hypothesis must be refutable. In other words, the test of the hypothesis must allow for the observation that the rock will not fall to the ground when released. Like electrons, no one has ever seen gravity, but because of the scientific method of supporting or refuting hypotheses about gravity, there is overwhelming evidence that gravity exists.
Now if we turn to the safety assessment process for biotech crops, we can see more clearly why a scientist using the scientific method can never prove that the crops are safe. To test hypotheses about the risk of biotech crops to human health, the hypotheses must be subject to testing and refutation. Remember, hypotheses can not be proven true, but they can be disproved.
In the United States, determining whether human health risks from consuming foods derived from biotech crops are acceptable or unacceptable is the primary responsibility of the Food and Drug Administration (FDA). The determination of “is it safe enough” is a societal decision that involves much more than science. However, science and the scientific method do form the foundation upon which the decision is made. For crops produced using recombinant DNA technology, the FDA evaluates the new protein that has been introduced into the crop. Proteins that typically are considered safe (or that pose negligible risk) have the following characteristics:
- They are from sources with no history of toxicity or allergy
- They do not resemble known toxins or allergens
- They have well understood functions
- They are expressed at low levels (major allergens are usually found in large amounts in allergenic foods)
- They are rapidly degraded in the stomach (within minutes)
- There is a lack of adverse effects in mice at high levels of consumption
- Animal feeding studies (42-day poultry trial) do not reveal any adverse effects
To evaluate the characteristics described above, the FDA regulator evaluates data from the following studies:
- Acute oral toxicity in mice (Is the protein toxic when ingested by a mouse?
- In vitro digestibility under simulated gastric conditions (How quickly does the protein break down in conditions that mimic the human stomach?)
- Comparison of amino acid sequence similarity of the protein to known protein allergens (Is the protein structurally similar to proteins that we know are allergenic?)
- Thermolability of the protein (Does heat, such as we might see in food processing or cooking, break down the protein?)
- Protein expression in plant tissues (Where in the plant does the protein occur and in what amounts?)
- Protein fate in parts of the plant and in processed food fractions (How do the amounts of protein in different parts of the plant change over time and how much protein is present as the harvested crop is being processed into food?)
- Poultry feeding studies (Are there any differences between chickens fed the biotech crop and those fed a non-biotech crop over a 42-day period? This type of study gives the regulator some idea of potential long-term dietary risks associated with humans eating food with ingredients from biotech crops.)
What is important to recognize here is that none of the results from the studies alone or in combination prove anything. In particular, they do not prove that human health risks from biotech crops are acceptable or that they are safe. Each study tests a hypothesis. For example, the acute oral toxicity in mice study is centered around the initial hypothesis that the dose or doses of protein administered to the mice will not result in mortality or any signs of toxicity. The results from all of the studies are evaluated by the FDA regulator, who makes a decision about the food safety of the biotech crop. The regulator, therefore, utilizes a weight-of-evidence approach when making his decision. The results either provide a weight-of-evidence that the protein is safe to consume or that it is not safe to consume.
Next Section: I DON’T CARE WHAT THE SCIENTISTS SAY—BIOTECH CROPS ARE TOO RISKY
Risk as Perception