Teaching materials : 3-5 teachers' lounge :
Avoid common teaching pitfalls
Ever wonder if your students left class confused? Confusion can be a good thing if it causes students to think through ideas for themselves and find solutions. But sometimes confusion leads to persistent mistaken impressions or to major misconceptions. You may wish to learn more about these misconceptions. Meanwhile, here are a few things you can do to avoid unintentional confusion when it comes to teaching your students about concepts related to evolution:
- Choosing your words carefully
- Clarifying misconceptions
- Scientific terms that leave the wrong impression: Survival of the fittest
- Correcting outdated information
- Slippery slopes in common classroom activities
Choosing your words carefully
Sometimes two terms are used interchangeably in the vernacular but have distinct meanings in science. Teachers need to be cautious of their own usage of these terms and encourage students to use this language correctly.
Function not purpose
The purpose of a hammer is to pound nails, and one's purpose in using the hammer might be to build a bench. However, it's not appropriate to say that one purpose of a hand is to hold a hammer. Instead, you can say that one function of a hand is to grasp or grip. Designed tools and independent agents have purposes. Structures of living things have functions. So, for example, it is preferable to say that the function (not purpose) of wings is flight or that wings are used for flying. Since purpose implies design or intent, this is an important distinction in the science classroom.
Adaptation not design
Use of the word design may imply that living things are designed and there is a plan at work. It is more appropriate to use terms like structure and adaptation when referring to organisms. For example, "How is an aardvark designed to eat ants?" should be replaced by, "What adaptations do aardvarks have that allow them to eat ants?" or, "What structures and behaviors aid an aardvark in eating ants?"
Evidence not proof
We often hear news stories that refer to a scientific idea having been proven. This is an example of confusing the terms proof and evidence. The term proof is used in mathematics and in courts of law, but does not belong in science because it implies absolute certainty. Scientists gather evidence which might help support or refute hypotheses and theories, but these ideas can never be absolutely proven, even when supported by many different lines of evidence.
In casual conversation we might hear, "My theory is that the Niners are gonna win the big game," when what is really meant is "I've got a hunch about who is going to win the football game this weekend." Socially, the first version is perfectly acceptable, but in scientific terms, a theory is much, much more than a casual hunch. This misuse reflects a persistent misconception about scientific theories. In the classroom, subtle differences in phrasing can reinforce or discourage such misconceptions. Here are a few cases in which watching your words can really pay off in terms of helping students build accurate conceptions. For more, visit our page on misconceptions regarding evolution.
In everyday language it's appropriate to say that we adapt to a new working environment or that a dog adapts to cold weather by growing a thicker coat. Unfortunately, students may apply this use of the term to evolution. This results in the erroneous impression that evolution consists of individuals adapting to changes in their environments within their own lifetimes. Evolutionary adaptations, on the other hand, occur through the action of natural selection working on populations of genetically varying individuals. Some of those genetic variations may have advantages over others in that environment and so will increase in frequency over the course of many generations.
Learn more about misconceptions regarding adaptation and natural selection.
Theory versus hypothesis
Much confusion surrounds these two terms because of common misconceptions and colloquial meanings that conflict with the terms' scientific meanings. In everyday language, we often use the word theory interchangeably with hunch. In science, however, a theory is much more than a hunch; it is a broad, natural explanation for a wide range of phenomena. Theories are concise, coherent, systematic, predictive, and broadly applicable, often integrating and generalizing many hypotheses. Theories accepted by the scientific community are generally strongly supported by many different lines of evidence, but even theories may be modified or overturned if warranted by new evidence and perspectives. Gravitational theory, for example, attempts to explain the nature of gravity. Cell theory explains the basic unit of life. Evolutionary theory explains the history of life on Earth, is supported by many lines of evidence, and is accepted by the scientific community. Describing evolution as "just a theory" conflates the scientific and everyday meanings of the word and is inappropriate.
In everyday language, the word hypothesis usually refers to an educated guess or an idea that we are quite uncertain about. Scientific hypotheses, however, are much more informed than any guess. They are explanations for a fairly narrow set of phenomena and are usually based on prior experience, scientific background knowledge, preliminary observations, and logic. In addition, hypotheses are often supported by many different lines of evidence in which case, scientists are more confident in them than they would be in any mere "guess." To further complicate matters, science textbooks frequently misuse the term in a slightly different way. They may ask students to make a hypothesis about the outcome of an experiment (e.g., table salt will dissolve in water more quickly than rock salt will). This is simply a prediction, an expectation, or a guess (even if a well-informed one) about the outcome of an experiment. Scientific hypotheses, on the other hand, have explanatory power. A more scientific (i.e., more explanatory) hypothesis might be "The amount of surface area a substance has affects how quickly it can dissolve. More surface area means a faster rate of dissolution." This hypothesis gives us an idea of why a particular phenomenon occurs and it is testable because it generates expectations about what we should observe in different situations (e.g., table salt will dissolve more quickly than rock salt will). Textbooks and science labs can lead to confusions about the differences between a hypothesis and an expectation regarding the outcome of a scientific test.
To learn more about hypotheses and theories, visit the Understanding Science website.
Scientific terms that leave the wrong impression: Survival of the fittest
For many people, this phrase suggests that evolution only gives a pass to the best of the best. However, a better way of expressing how natural selection works is "survival of the fit enough." Portraying nature as a constant life-or-death struggle against competitors grossly oversimplifies what is really going on. Many life forms get by for eons by existing in niches for which other organisms are not suited or by simply being "good enough" to get their genes into the next generation. For example, brine shrimp live in water that is unsuitable for potential aquatic enemies, and they apparently have no significant competitors for food.
Also, it may be important to remind students that natural selection is not just about survival. To pass their genes on to the next generation, organisms must both survive and reproduce. By focusing on survival, the phrase "survival of the fittest" may encourage students to overlook sexual selection and the key role that reproduction plays in evolution by natural selection.
Learn more about misconceptions regarding adaptation and natural selection.
Correcting outdated information
With new research and new perspectives, science advances and helps us understand the world around us more clearly. The fact that all scientific knowledge is fundamentally tentative and may be modified over time is one of science's great strengths, but it also means that the information that is in your textbook or that was in your college biology course can rapidly become outdated. Here are a few updates.
Defining a reptile
In grade school, many students learn that reptiles are cold-blooded, land-dwelling vertebrates with scales. However, in modern biological classification (which is based on evolutionary history) birds are a part of the clade Reptilia because, on the tree of life, the birds are a small twig on the reptile's branch. (In fact, according to modern biological classification, birds are also considered to be dinosaurs because they evolved from this particular group within Reptilia.) So, strictly speaking, reptiles are not just cold-blooded, scaly creatures; they are also warm-bodied, feathered creatures. This can prove to be a challenge in the classroom since the word reptile is used colloquially in one way and scientifically in another. Furthermore, it's useful to have a word that refers to animals that meet our traditional definition of a reptile. (For comparison's sake, the living amphibians do form a distinct clade and so this term can be used both colloquially and scientifically in the same way.) What's a teacher to do? One solution is simply to keep this detail in mind as a teacher of younger students and ensure that the issue of the phylogenetic classification of reptiles is explicitly addressed when students are older. Another possible approach is to use the word reptile only in the strict, scientific sense, and to teach students that snakes, lizards, turtles, and crocodiles share certain key features like cold-bloodedness, scales, and egg-laying.
Learn more about the phylogenetic definition of a reptile.
Great apes without humans
It is common to use the words great ape to refer to chimpanzees, bonobos, gorillas, and orangutans. However, this reflects an outdated view of classification. Humans are the closest living relative of chimpanzees and bonobos, and their branch on the tree of life is nested in among gorillas and orangutans. There is no unique set of traits that set chimpanzees, bonobos, gorillas, and orangutans apart from humans. Technically speaking, humans are not just closely related to great apes; we are great apes. You can reinforce the correct conception with phrasing such as "The great apes, including humans, are omnivorous."
Slippery slopes in common classroom activities
Evolution is more difficult to observe than, for example, Newtonian physics. Thus, we often conduct activities in the classroom that are intended to be analogous to evolution and to the scientific enterprise. However, some of these activities can lead to misconceptions unless they are carefully planned.
A very common activity for young children is to have them make "fossils" by pressing shells into clay or plaster of Paris. While this clearly shows how a rock can contain molds and casts, it may well mislead children about the process by which fossils are formed in nature. In most cases, shell fossils are formed when shells are covered by sediment and over time the sediment hardens. This is very different from the process of squashing shells between two slabs of clay. If used with younger students, it is better to have students learn that you can identify what has left an imprint by looking closely at the imprint. And then if the students are old enough, a comparison can be made to studying fossil imprints.
Design an animal
When we ask students to design an animal to fit an ecosystem, on paper or out of pipe cleaners, we may be sending the message that living things are designed or that an individual animal can "adapt" to its environment by choosing to do so. This is far from the scientific view that living things are adapted over time to their environmental situations through genetic variation and natural selection. If you use such activities be sure to clarify for students how what they are doing contrasts with the natural processes of evolution.
Having students hypothesize (guess) before they know anything
Hypotheses are explanations for natural phenomena that are based on prior experience, scientific background knowledge, preliminary observations, and logic. There are two main ways in which activities misuse the idea of having students form hypotheses. First, they may ask students to formulate a hypothesis without any prior knowledge or experience. This does not reflect the way science actually works and so should be avoided. If you want students to make a guess, that's fine just be sure to call it a guess, not a hypothesis! Second, many activities ask students to form a hypothesis about what will happen in a particular situation or in a particular experiment. This conflates the idea of a hypothesis with that of an expectation. Hypotheses are explanations. There is nothing explanatory about the prediction that plants that get more water will grow taller or that students wielding tweezer-"beaks" will pick up the most lentils off the carpet so these are not hypotheses. Rather they are expectations generated by the hypotheses that water is a critical component of plants' growth process and that a small "beak" is most efficient at picking up small food items. Be sure to help students distinguish between ideas that are true explanatory hypotheses and those that are merely what they think is going to happen. You can help students formulated real hypotheses by probing them about why they expect one outcome and not another to occur.