Despite the fact that 2015 is the tenth anniversary of the pivotal Kitzmiller v. Dover Area School District decision prohibiting the practice, creation science and intelligent design are still taught in far too many classrooms: perhaps more than one in eight, according to a 2011 survey. Outright denialism and overt teaching of non-science, however, is only part of the problem at the heart of America’s issue with evolution. Another part, which involves misconceptions about evolution, is far subtler. Such misconceptions have a variety of sources, but their effect, building up slowly over time, is to impair student understanding of evolution. As a result, the students are vulnerable to confusion and doubt about evolution in particular, or even science in general, after they leave school.
So what are some of the biggest misconceptions about evolution, how do you spot them, and what can you do about them? We’ll cover the first two in this installment, and three more in the next one.
Misconception #1: Natural selection and evolution are the same thing.
Correction: Evolution, or descent with modification, describes any change in the distribution of heritable traits within a population over time. A mouthful, I know, but “change over time” is too simplistic—weather changes over time, but you wouldn’t say that weather evolves. Confusing and conflating scientific and common usage of terms, such as “evolve” or “adapt,” exacerbates many of the misconceptions I’ll discuss. An important lesson to impart to all students—and scientists, and science communicators, and, well, everyone—is the importance of context in understanding language. So evolution is heritable change in a population over time, but what is natural selection? Natural selection is one mechanism—a very important mechanism, but still just one—of evolution. Others include genetic drift, gene flow, and mutation.
What this misconception looks and sounds like: In the classroom, look for students interchanging the two concepts and terms as if they are synonymous. For example, “Evolution explains how the characteristics of populations change over time and occurs when the environment favors certain variations over others.”
What to do about it: When covering evolution, be sure to emphasize that natural selection is one of several mechanisms of evolution. It could very well be the case (as in the Next Generation Science Standards) that your curriculum does not explicitly call for exploration of the other mechanisms, but that doesn’t mean you need to give students the impression that it’s natural selection or nothing. You can explain that there are other ways that evolution occurs, but in class, you’ll be focusing on one. If you get an answer along the lines of my hypothetical example, push back a little. Tell the student, “What you’re describing is natural selection—remember! Evolution occurs in other ways, too.”
I expect, however, that you at least touch on the other mechanisms in your existing suite of evolution lessons. For example, if you go over the diversification of the finches in the Galápagos (and who doesn’t?), you cover not just natural selection but also genetic drift—even if you don’t identify it by name. Recent research has highlighted the role of gene flow in human evolution (your students will love talking about Neanderthal–Homo sapiens interbreeding!), and mutation, itself a mechanism of evolution, is a part of almost any evolution case study. The next misconception is a direct consequence of the last one.
Misconception #2: All traits are adaptive.
Correction: A lot of traits are adaptive—but definitely not all. If you want an example of a trait that isn’t adaptive, look no further than your own belly button. A belly button is a scar left from the umbilical cord connection that sustained development. The umbilical cord? Definitely an adaptation. Its scar? Not so much.
The belly button is an example of a non-adaptive byproduct, but there are other kids of non-adaptive traits, too. For example, tetrapods, such as humans, typically have five digits—why five? There is probably no good reason—it just happened that way. Fingers and toes are of course adaptive, but the specific number of them? Not so much.
What this misconception looks and sounds like: Look for students to ask what everything is for—it’s so easy when learning about such incredible adaptations as the proboscis of Darwin’s hawk moth to the color-changing ability of the octopus to think that everything is for something, so they’ll ask that question again and again. Also look for the inverse—the dread “X evolved for Y,” as in “feathers evolved for flight.”
What to do about it: The best way to make students see the fallacy of the hyperadaptive view of life is to point out clear examples of non-adaptive traits, so talk about belly buttons and male nipples! Provide examples to help students understand that adaptive functions can change (whale hip bones) and even be lost (human tail bones). Also, introduce an adaptation litmus test: To be an adaptation for a particular function, the trait must be heritable, have the function it was selected for, and increase fitness. Return to the litmus test again and again as you discuss everything from peacock tail feathers to dinosaur forearm feathers.
So evolution occurs via several mechanisms and not all traits are adaptive. This may somehow feel like a de-emphasis of natural selection, and in a way it is—but it is not a de-emphasis of evolution. Cracking down on these misconceptions, and the ones I’ll discuss in the next part of this post, will give your students a more sophisticated understanding of evolution, and by extension, a more sophisticated understanding of the world around them.