When it comes to teaching classification, you may be using a text book with outdated information.
The superfamilies, the supergroups, the superdupergroups...the cladistics vs. the evolutionary systematics vs. the wait-a-second-they-actually-overlap-more-than-we-thought ... you feel me?
I open up my classification unit with the Father of Taxnomy: Carolus Linnaeus. I ask my students if Linnaeus knew about the findings of Mendel, or Darwin, and so on. And, with some simple math, they can figure out that Linnaeus came before their time, and had no notion of natural selection, genes, or DNA. He was pretty boss at organizing plants, though. And his system works, and it it works pretty darn well! But, what we have to acknowledge is that Linnaeus' system is 300 years old. And we've come a long way since then. So with that, comes 5 Helpful tips for teaching classification in a modern world.
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1. THE BASICS- The why and the how: Students are typically able to absorb the taxonomic levels easily. The focus should be that as you move down the levels, the number of species decreases, but the similarities increase. This notion is more important than memorizing the order of the taxonomic ladder; but they should know the order for the sake of knowing that a Kingdom will hold more species that have a wide range of traits vs. a Family that will have fewer species with fewer differences/more similarities. A mnemonic is most likely the most effective way to encourage this. Keep Piling Chocolate on Fred's Gooey Sundae is my personal favorite.
Another important note about the taxonomic levels is the scope and the diversity. I like to show students how diverse the kingdoms are by incorporating some visual posters about the different phyla found in the kingdoms. The idea is simple: each student is assigned a particular phyla within a Kingdom and they make a poster (or any type of visual), which we would then hang on our classroom bulletin board. This would give students a quick visual glance of how diverse the kingdom was. One might look something like this...
Finally, to help students get the big picture behind why classification is important for studying organisms, you can enhance the introduction of your classification unit with a freebie I offer in which students need to help plan the layout of a zoo. (Link, along with other useful links, found at the end of the post).
2. Give students practice as a prac- prac- practical! They love classifying stuff! You give them some examples with a few descriptions and they go nuts! It's really easy, too! You just need some specimens! I truly do believe this is the best way to familiarize themselves with the different types of kingdoms. It's super easy and super fun! I make a table with different cell characteristics that students can fill out as they go along (such as presence of cell wall, chloroplast, etc.)
If you have random things laying around (coral, frog skeletons... or random pieces of said frog skeleton... jarred specimens, microscope slides, etc., you can easily use them in this lab practical.)
For example, here's a molted cicada exoskeleton I found in my yard- perfect specimen for a classification practical in the classroom! You could use feathers to represent birds, bark to represent a tree; the list goes on! Just make sure you have all the kingdoms covered. I once printed out a picture of a mushroom and wrote "pretend this is real"- ha! But a trip to the grocery store or backyard could have provided a tangible specimen.
3. The task of classification isn't fully appreciated unless they do it themselves. Yup. 'Das right. That whole "tell me and I forget...show me and I remember... make me do it and I'll never forget it!" If you have your students classify things and ask them make a dichotomous key, they will understand...absorb...learn. In order to do this, I'd have them classify an alien planet. They have to group the made-up organisms found on a distant alien planet and then make a dichotomous key. At this point, some students do not yet understand that organisms should be grouped by similarities (even though you've told them... they need to do it themselves to truly understand). For this project I'd group the students and always try to pair a student who strongly understood the material with one who was struggling or not showing that they understood during formative assessment. They won't mind, it's fun and they are problem solving and gaining a greater appreciation for Linnaeus's system.
You can have students use pretty much anything: candy, leaves, beans, shells, etc. Have them each bring in a stuffed animal from home if you are low on resources.
And it doesn't need to be "right" or "wrong"; you could always use this as a formative assessment, and have groups volunteer to share how they classified.
4. DNA and evolutionary systematics are now a big part of classification. Classification should come after you've taught both DNA and evolution. This information does not need to be presented in an unbridged, disconnected fashion when we can tie it in nicely. 🙂
Now that students know all about the taxonomy levels, why and how we classify, we can bring in the ultimate weapon of classification: DNA. It's important to mention that Linnaeus' time was before Mendel and Darwin; you can use that as a bridge to modern classification. Give your kiddos examples and fill in the gaps together as you make your way into evolutionary systematics!
When classifying organisms, we've learned that looks can be deceiving, which is why DNA is an important theme. Here are two example that I used in my classroom to show how you can't always rely on physical appearances alone when classifying:
- Barnacles (actually more closely related to crustaceans than gastropods).
- American vultures (actually more closely related to storks than other vultures).
(If this interests you, more on these examples is found in a piece of literature I've written to guide students through this: "Classification: Beyond Linnaeus.")
This is also the perfect opportunity for a little inquiry! Ask students what DNA can tell us and how it can perfect our classification system. It's a wonderful tool to use!
5. Evolve: DNA. Phylogenies. Evolutionary Systematics. Derived Characters. Ancestral Characters. Clades. When teaching classification nowadays, these terms should be covered.
Some things to ask yourself before you get started in modern classification: What role does DNA play in modern classification? How has this new information changed how we classify? What are the differences among cladograms and evolutionary trees? Can you distinguish one from the other? What is the overlap between the two? How would you approach this with students?
Your class has most likely been focusing a lot of the time on similarities used to group organisms, but now we need to introduce differences and how we use these differences to create cladograms. Review with your students ancestral vs. derived characters. This will help your students better understand how to construct a cladogram.
From there, I typically review speciation and phylogenies before entering evolutionary trees.
Traditionally, the focus has been that cladistics and evolutionary systematics are different, and those there still tend to be differences, the two concepts are merging. I noticed that in my first years teaching I covered the differences between evolutionary systematics and cladistics in detail; but now I spend more time focusing on the big picture.
In a nutshell: cladograms and evolutionary trees can be used interchangeably, but generally there are some slight differences. Evolutionary trees depict how ancestors are related to descendants, and can tell us how much the organisms have changed. Evolutionary trees are baed on ancestry, rather than derived characters, and branch length represents time.
How do you approach cladograms and evolutionary trees? If you need a resource to guide your students, check out Classification: Cladograms vs. Trees
(more useful links below!)
Lastly, some useful links for teaching classification: Organizing Information Freebie- to help students better understand why classifying animals is important in order to study them.
If you choose to do a diversity poster like the one pictured above, your students can use the Animal Diversity Site as a great starting point.
My favorite online resource for modern classification, or phylogenetic systematics, is Berkeley: Phylogenetic Systematics. There is a plethora of information and they present it in a clear and concise way!
If you'd like to browse a list of high quality classification resources you can use in your classroom, check them out at Biology Roots: Classification
