The scientific method is a detailed, empirical, problem-solving process leveraged by biologists and scientists of other disciplines. This iterative approach involves formulating a question based on observation, developing a testable potential explanation for the observation (called a hypothesis), making and testing predictions based on the hypothesis, and using the findings to create new hypotheses and predictions.
Generally, predictions are tested using carefully-designed experiments. Based on the outcome of these experiments, the original explanation may need to be refined, and new hypotheses and questions can be generated. Importantly, this illustrates that the scientific method is not a stepwise recipe. Instead, it is a continuous refinement and testing of ideas based on new observations, which is the crux of scientific inquiry.
Science is mutable and continuously changes as we learn more about the world around us. For this reason, scientists avoid claiming to ‘prove’ a specific idea. Instead, they gather evidence that either supports or refutes a given hypothesis.
A hypothesis is preceded by an initial observation, during which information is gathered by the senses (e.g., vision, hearing) or using scientific tools and instruments. This observation leads to a question that prompts the formation of an initial hypothesis, a (testable) possible answer to the question. For example, the observation that slugs eat some cabbage plants, but not cabbage plants located near garlic, may prompt the question: why do slugs selectively spare cabbage plants near garlic? One possible hypothesis, or answer to this question, is that slugs have an aversion to garlic. Based on this hypothesis, one might predict that slugs will not eat cabbage plants that are surrounded by a ring of garlic powder.
A hypothesis should be falsifiable, meaning that there are ways to disprove it if it is untrue. In other words, a hypothesis should be testable. Scientists often articulate and explicitly test for the opposite of the hypothesis, which is called the null hypothesis. In this case, the null hypothesis is that slugs do not have an aversion to garlic. The null hypothesis would be supported if, contrary to the prediction, slugs eat cabbage plants that are surrounded by garlic powder.
When possible, scientists test hypotheses using controlled experiments that include independent and dependent variables, as well as control and experimental groups.
An independent variable is an item expected to have an effect (e.g., the garlic powder used in the slug and cabbage experiment, or treatment given in a clinical trial). Dependent variables are the measurements used to determine the outcome of an experiment. In the experiment with slugs, cabbages, and garlic, the number of slugs eating cabbages is the dependent variable, as this number is expected to depend on the presence or absence of garlic powder rings around the cabbage plants.
Experiments require experimental and control groups. An experimental group is treated with or exposed to the independent variable (i.e., the manipulation or treatment). For example, in the garlic aversion experiment with slugs, the experimental group is a group of cabbage plants that are surrounded by a garlic powder ring. A control group is subject to the same conditions as the experimental group, with the exception of the independent variable. Control groups in this experiment might include a group of cabbage plants in the same area that is surrounded by a non-garlic powder ring (to control for powder aversion) and a group that is not surrounded by any particular substance (to control for cabbage aversion). It is essential to include a control group because without one it is unclear whether the outcome is the result of the treatment or manipulation.
If the results of an experiment support the hypothesis, further experiments may be designed and carried out to provide support for the hypothesis. The hypothesis may also be refined and made more specific. For example, additional experiments could determine whether slugs also have an aversion to other plants of the Allium genus, like onions.
If the results do not support the hypothesis, the hypothesis may need to be adjusted based on the new observations. Problems with the experimental design should also be ruled out. For example, if slugs demonstrate an aversion to both types of powdered substance, the experiment can be carried out again using fresh garlic instead of powdered garlic. If the slugs still exhibit no aversion to garlic, the hypothesis may be adjusted. In this example, the new hypothesis may be that slugs have an aversion to powder.
The results of the experiments should be communicated to other scientists and the public, regardless of whether the data support the original hypothesis. This information can guide the development of new hypotheses and experimental questions.
