Hopefully, you have arrived here after dealing with the topics suggested in the overall unit sequence plan (nature of science, survey of the diversity of life, biological classification, and a look at the evidence for human evolution). Alternatively, you may prefer to introduce the topic of evolution directly, or at least with some preliminary effort to address the common misconceptions about the nature of science, and are doing these things fairly early in your course. In either case, your students should be primed to take a closer look at this thing called "evolution", what it IS and what it is NOT.
If you haven't already "pre-tested" your students to reveal any misconceptions about evolution they bring to your class, now would be the last opportunity to do that. One way to do this is to administer an "Evolution Survey" , which asks students to respond to a number of statements with a "true" or "false" according to how they think biologists understand evolution (NOT necessarily whether the student agrees with it or not). Afterwards, you can have students check their own papers as you give the answers and briefly comment on the reasons for those answers (many to be explored later in the unit, mostly with lessons on this site). Alternatively, you can just collect and score the answer sheets yourself, perhaps treating this as "pre-test" results, to be compared with an identical test given at the end of the unit or course, to assess student progress and/or the effectiveness of your teaching this unit. CLICK HERE for a handy Pre/Post Test Analyzer (Excel file). This will tell you the individual and class averages for the % change between Pre- and Post-Tests.
You may find it very interesting if you can do an item analysis of the responses, both in the pre and post tests. Click here to see a sample "Evolution Survey" which has worked very well. If you wish to see the proper responses for this Survey, with clarifying comments, or you want a copy of the test in Word format, send your request to the Webmaster using your school email address. For the rationale to the proper responses, see the What Evolution is NOT (below), and the more detailed Evolution Unmuddled. To see a recent study showing the value of using an Evolution Survey or pre-test. Click HERE.
Here is a sample testimonial to the effectiveness of using the Evolution Survey: "Thank you for the new survey. I have been using the survey with great success each year. We do the survey at the start and I correct it and tell them each how many they missed. As we go through our lengthy discussion on evolution and natural selection (around 12 weeks!), I make sure to hit each question in the survey and discuss why it is true or false and the common misconceptions surrounding it. The results when we take the survey again are great. It's a very valuable learning tool. Eliza."
VARIATION ON THIS SURVEY: Some teachers have considered giving a variation of the above Evolution Survey, in which the instructions have been changed to say "... in terms of how YOU understand evolution..." Even more interesting, if you have the time, give this modified version first, emphasizing that your students answer according to their own personal understanding at this moment. Then, perhaps the next day, give the one we have here: "...answer in terms of how you think biologists use and understand the term 'evolution' today." If you do this, let us know how much their scores differ, if at all.
Probably the best and most concise collection of rationales that support the answers in our Evolution Survey is an article from Scientific American (July, 2002) on "15 Answers to Creationist Nonsense." You could even build your own evolution survey around this. This article is mainly for teacher information. It might not be wise to hand out (8 pages) to your students, as it's title and some comments there might offend some students (and parents), perhaps subject them to ridicule by others, or make them defensive so that they would resist any efforts for an objective study of evolution. I've found that it's much more effective to follow the pre-test with numerous experiences (e.g., many of the ENSI lessons), in which they discover what science does say (and the compelling evidence for that), and then they may begin to recognize personally that some of their perceptions were simply incorrect. Hopefully, a post-test will reveal that. Check out our "Teaching Units for Biology," especially my "Evolution Solution" for effective strategies that do that.
Also, see the American Biology Teacher, August 2007, page 332: "Reliability of the Measure of Acceptance of the Theory of Evolution (MATE) Instrument with University Students." The MATE is a 20-item multiple choice testing instrument that measures the degree of acceptance (or non-acceptance) of evolution theory. The article reports a study that gives the test high marks for its reliability. It is suggested as a tool, in a pre-/post-test sequence, to assess the effectiveness of different strategies for teaching evolution that emphasize the nature of science as a method of inquiry and critical thinking. Note that this measures student acceptance of evolution rather than their perceptions for how biologists use and understand the term "evolution," as the Evolution Survey (on the ENSI site) attempts to do. In either case, the tests provide useful assessments of the level of misconceptions that are held by the students, exposing important targets that should be addressed in the course. I strongly recommend reading the article, and considering the use of the MATE test as an alternative to the Evolution Survey, depending on which measure you prefer. The MATE test is included in the article, along with its scoring rubric. If you would like to see a copy of the article, please contact the webmaster.
With or without the "Evolution Survey", very early in this general introduction to evolution, it is wise to dispel at least some of the popular myths many people believe about evolution. Plan to take a whole period to go over "What Evolution Is NOT", then a brief overview of what it IS. It is bound to raise some questions, so be sure to invite such questions, so they can be openly and readily discussed. You may prefer to have your students hold their questions until after going over the list of 12 things evolution is not. For an extended discussion of the rationale to the statements as asserted in the Evolution Survey and the What Evolution is NOT paper, read Evolution Unmuddled and "15 Answers to Creationist Nonsense." (see above for suggested use of this source).
In addition to the descriptive paragraphs of what evolution IS, we have a nice simplified
diagram of an evolutionary tree you can use to illustrate that
description. It's also useful to relate the classification hierarchy
to evolution, and also to show how "microevolution",
over time, can result in "macroevolution".
MACROEVOLUTION DIAGRAM: See the Macroevolution Diagram and a page of directions for using that diagram on an overhead projector. This nicely shows how accumulated speciations can eventually form all the groups and subgroups of organisms. It also shows how classification is related to evolution. A very nice colorful version of this can be found on page 32 of that most useful resource: Teaching About Evolution and the Nature of Science, by the National Academy of Sciences (1998) (see our Resources section - first book in the list). A particularly interesting alternative diagram is the one Darwin included in The Origin of Species (chapter IV), the only diagram in that book! His discussion there of that diagram should be required reading for any biology teacher. Darwin's Tree makes a great overhead transparency for discussing his concept of evolution by natural selection, as well as how classification reflects that evolution. To read Darwin's description of that tree diagram, go to chapter 4, and the section titled "Divergence of Character". You can read this directly in his original edition on the TalkOrigins site - Chapter 4. Be sure to have the Darwin's Tree diagram handy, as it is not included in that text.
At some point within your "Intro to Evolution" unit, especially if you (or your text) introduces Lamarck's pre-Darwinian effort to explain the mechanics of evolution, you might find it productive to clearly contrast these two ideas. For some strange reason, many students seem to gravitate toward explaining Natural Selection using phrases and terms reflecting Lamarck's hypothesis! Phrases like "leopards evolved their spots IN ORDER TO survive better in their environment", or, "Elephants evolved their large ears SO THAT they could disperse their body heat better." Perhaps it's our (natural?) tendency to "anthropomorphize" (I call this "The Mickey Mouse Syndrome"), or perhaps it's only a reflection of widespread confusion about the process, frequently reinforced by the popular media, and even some textbooks and well-meaning teachers.
In presenting Natural Selection, you may find it useful to illustrate each part (or step) with color slides or overhead transparencies showing familiar examples of each. Make every effort to dramatize this for maximum impact and long-term memory retention.
In addition, there are at least a few terms and concepts which
frequently make their inappropriate appearance in this unit,
even in textbooks and videos, leading to fuzzy understanding.
1. Only GROUPS of organisms can evolve (populations or species). Individual organisms NEVER evolve. Which brings up the problem of using "organisms" without clearly indicating whether it pertains to groups or individuals.
2. ADAPTATIONS, (no such thing as "adaptions") in the evolutionary sense can only "develop" as characteristics of a species, over a long period of time, involving many generations. In contrast, in its NON-evolutionary sense, the word is often applied to the changes INDIVIDUALS make (consciously or otherwise) which enable them to survive better in their environment, e.g. "developing resistance to disease" or "adapting to higher altitudes", etc. Every effort should be made to point these things out, and to demand clear and proper usage in class. You might encourage the use of other words here, e.g. "adjustment" or "acclimatization". Because of this potential for misuse, it's probably best to avoid using "adaptation" as equivalent to the process of evolution, or natural selection, and even avoid using "adaptations" for the product of evolution.
3. Evolution is NOT the same thing as natural
Evolution, the process in which all forms of life have arisen from earlier forms, is a fact, meaning that it is a very real process: the tangible evidence is very clear, mostly from fossil and molecular studies.
Natural Selection is also a fact; it is observed daily in the form of bacterial resistance to antibiotics, viral resistance to anit-virus treatments, and insect resistance to insecticides. It has also been observed in natural populations over time (e.g. documented beak changes in Galapagos Finches over several years, reflecting significant climate changes), and it has been observed in countless laboratory studies.
The explanation that evolution results from natural selection is a well-established, abundantly supported theory: a very likely explanation for the (central) mechanism of evolution, a process which creates new traits and new combinations of traits, forming new species. Other mechanisms are also operating in the process of speciation, e.g. genetic drift and isolation. The relative influence of all influential aspects, and the detailed pathways for the evolution of specific traits and species constitute the main areas of dialogue and for most research in evolution today.
BOTH of the above (Comparing Mechanisms of Evolution, and Common Misconceptions) have been collected on a single two-sided sheet for handout, including a sample exercise for students to recognize whether a particular scenario is a Darwinian explanation, or a Lamarckian explanation, encourages discussion of this, and asks them to write their own two scenarios, using some other traits and/or creatures, one version according to Darwin, and one according to Lamarck. You will find this package (along with a key) in downloadable PDF format below. You might also find it useful to prepare an enlarged version from which to make overheads to facilitate discussion.
NATURAL SELECTION MISCONCEPTIONS
Be sure to read the article by T. Ryan Gregory: Understanding Natural Selection: Essential Concepts and Common Misconceptions." This enlightening article was published in the Evolution Education & Outreach Online for June 2009 (vol.2 no.2). It clearly addresses the many misconceptions about natural selection. Studies show that even many college biology majors and biology teachers unknowingly carry some of those misconceptions - and are passing them on to their students. The author offers tips into how teachers might be able to help their students discover where their understandings miss the boat, and how to repair them. This article is a must read.
For a brief review of this article (along with several other articles, mostly on transitional fossil series and the proper use of phylogenetic trees and cladograms), CLICK HERE.