Every Feb. 2, crowds gather in places such as Punxsutawney, Penn., and Staten Island, N.Y., to find out whether there will be six more weeks of winter—all riding on whether a groundhog sees its shadow. Does the groundhog shadow impacting the length of winter show cause-and-effect?
Statistical studies have found that the divorce rate in Maine from 2000 to 2009 closely matches the per capita consumption of margarine. Is this correlation an example of cause-and-effect?
The relative positions of the Earth, moon, and sun cause the observable phases of the moon. Is this cause-and-effect?
Increases in the release of anthropogenic carbon dioxide contribute to global climate change. How about this one?
As you probably guessed, the first two examples are not the result of a cause producing an effect, but the second pair are among the myriad of examples of this important crosscutting concept of the Next Generation Science Standards*. We all experience cause-and-effect every day, mostly outside of science applications. So we need to be able to help our students recognize true cases of cause-and-effect as well as how to identify spurious correlations that falsely imply this is happening.
Examples of Cause and Effect
You are familiar with many cause-and-effect situations in biology, chemistry, physics, Earth science, and technology. Some include:
- No matter how seeds are planted in soil, when they germinate, roots grow downward and stems grow upward—the result of gravity affecting plant auxins to produce “positive geotropism” in root cells and “negative geotropism” in the stems.
- If you add acidic solutions with alkaline solutions, the pH changes in predictable amounts.
- Mixing pigments creates new colors, such as blue and yellow combining to form shades of green.
- Pedaling a bicycle results in movements of the chain, gears, and wheels and the capability to go from place to another much more easily than by foot.
Cause-and-effect relationships often involve repeating patterns within the Earth system and its components. Scientists may seek reasons behind changes in holes in the ozone layer above Antarctica, population patterns in an ecosystem, or responses to levels of medication.
One of the first decisions most people make each day is what to wear, often influenced by the weather. Two centuries ago, most people believed weather was caused by their deities’ actions, sometimes as punishment for bad behavior. Now, we understand that atmospheric conditions result from interactions between air temperature, pressure, moisture, and other variables. The better we can be at making careful observations, identifying these relationships, and implementing design algorithms to solve complex numerical model calculations, the more accurate meteorologists will be in predicting that certain combinations of atmospheric variables will result in certain probable weather conditions.
In many cases, it may be impossible to identify with absolute certainty the cause behind an effect, so a probabilistic approach should instead be used. This is what often happens in predicting weather. Meteorologists examine all known factors, crunch them in their numerical models, and issue a statement in the form of a statement like: “There is an 80 percent chance of heavy snowfall.”
Earthquakes release seismic waves, including the surface waves that can produce damage to buildings, roads, and other structures. What causes earthquakes? The seemingly obvious answer is slippage at a fault zone. But where does the energy that causes such movements come from within the rocks? Can we measure in ways that will someday allow accurate predictions of the effects in advance of them happening? Often, recognizing cause-and-effect can significantly benefit society.
Cause and Effect in the Science Classroom
Many questions in science begin with observations and recognition of patterns. The next step in finding answers often involves trying to determine why or how things happen. A tentative answer (or “hypothesis”) often involves statements in the form of “If A, then B, because….” This requires seeking support that there is a chain of interactions that lead from A to B. Most science investigations involve designing tests that gather evidence to support or refute causes of observed change.
Even very young students can engage in demonstrations and experiments of this nature. For instance, they can explore differences in the effects of varying strengths of pushing and pulling forces on the motion of objects. Or, they could examine the effect of recycling on the use of resources. By the time students reach high school, the complexity of the problems being investigated and the sophistication of the experimental design should reflect their increased knowledge and abilities.
An approach that strongly aligns with the NGSS involves assisting students in developing their own explanations for observed patterns or phenomena. Consider what students may come up with as explanations for why a given animal population is decreasing: Could it be disease? Predation? Loss of habitat? Reduced food supply? Other factors? Encouraging students to present evidence-based arguments behind cause-and-effect situations will help form the skills they need for problem-solving after their formal education and throughout their lives.
One of the major differences between the NGSS and previous state standards is a greater integration of Science and Engineering Practices. Applying engineering-based approaches to studying problems and seeking solutions depends significantly on understanding cause-and-effect relationships between parts of the system. Better knowledge of relevant relationships will lead to more effective designs.
Rube Goldberg was a cartoonist famous for illustrating elaborately complex machines to accomplish simple tasks. Humorous as they were, they represent the pinnacle of the concept of cause and effect. One example is a Honda commercial from about a decade ago. Perhaps your students can try to design “Rube Goldberg machines” to develop their cause-and-effect understanding and skills.
Modern civilization depends on major technological systems, so our students should be assisted in progressing from simply recognizing cause and effect is happening to asking questions about how something happened and what mechanisms caused that to happen. Perhaps they can even, in appropriate situations, explore ways to make things happen differently for better results. Adequate water supplies will be a key challenge in many locations in future decades; students could seek new approaches to cleaning and reusing wastewater. New purification methods producing safe water would be a very desirable cause and effect!
And it is often important to consider cultural differences in developing scientific understanding. Research into how science affects culture and how culture affects science can be considered still in a rudimentary state, with very few studies producing definitive answers. Among well-known examples are acceptance of climate change and biological evolution. Lesser-known examples involve contrasts based on cultural mores of your students’ families when different from yours. You will encounter situations where cultural differences impact how your students treat “scientific” ideas, and it is essential that you can recognize when this is happening.
To sum up, understanding cause and effect plays an important role in what and how your students learn.
Dr. Passow hosted a free webinar, Exploring the Crosscutting Concept of Cause and Effect with Your Students, on Tuesday, May 8 at 7 p.m. Eastern Time. Watch the recording here.