Final Thoughts on Natural Selection...

...before moving on to heredity.

I don't believe for a moment that most of my students have mastered the concept. I know from a test that was given (using questions from old regents exams) that they are struggling to pull all the ideas together. This is not exactly unexpected. Evolution and natural selection take a while to sort out, the idea of change occurring over generations is difficult to grasp. A few students have latched onto Lamarckian explanations, and can't seem to get past the idea that adaptation happens to individuals, that it is somehow a matter of individuals "getting used to" environmental conditions.

I don't know where the Lamarckian ideas come from, it must be somehow intuitive, because I purposely didn't teach Lamarck's theory for fear of suggesting an idea that some of them might find attractive. I have now addressed the issue since it did come up in their analyses, but it will take some more work to get students past the idea.

I plan to weave evolution and natural selection into other topics whenever possible. I did take advantage of the discovery of Homo floresiensis to discuss human evolution briefly, although I hadn't planned on addressing human evolution until after we have done the heredity/genetics component. That way when we discuss DNA evidence of the chimp/human relationship, it will be more compelling. A full unit on modern synthesis, history of life on earth, and human evolution are scheduled for early next year, after we complete heredity & cell bio.

Finches' Beaks

New York State's Regents Exam for Living Environment includes questions that are based on 4 required lab activities. One of those labs is called The Beaks of Finches and is supposed to be a simulation of Natural Selection.

I wasn't impressed with the lab.

Let me first describe the idea. I would post the actual lab activity, but it is copyrighted by NY State and we are explicitly forbidden to distribute it except to NY State personnel involved in teaching it. In fact, the state does not make it available to us electronically, instead we must request hard copies directly from State Ed., so I wouldn't be able to post it anyway unless I scanned it myself.

There are other similar versions of the activity around: This one at Access Excellence is almost identical to the New York State version minus the student worksheets (It's the format and exact nature of the questions on the lab worksheets that are unique to NY State).

Basically, you need about 12 - 16 different grasping devices - tongs, tweezers, pliers, etc. - and 2 different kinds of seeds. I used extremely small lentils and fava beans. Students work in pairs, and try in 30 seconds to gather enough seeds to survive from a plate of seeds at each table. Average 13 seeds per round and you survive. Those who do not survive the first round (small seeds only) "migrate" to another island and try their beaks at larger seeds. In the second round, competition with another group is added to the activity. Anyone who doesn't survive the second round is "extinct."

The problem I had with both of my classes was that clearly technique was the deciding factor in surviving rather than the type of beak. I had small tweezers that come to a sharp point and large scissor-style tongs with wide flat tips (beaker tongs) and short heavy stubby pliers and variations on all those basic types. Absolutely no trend emerged that would allow students to see a connection between the type of beak and success in the struggle to survive. Granted, it is important for students to know that behavior (technique) can also be subject to natural selection, but that seems to me to be a finer point to stress AFTER students understand the basic concept as it relates to physical characteristics. Anyway, the activity is called Beaks of Finches, not Techniques of Finches. On that score, the activity fails miserably. Although there may be some interesting higher level discussions that could come out of this activity, for a demonstration of the basic principles of natural selection I would look for other simulations. It is probably not a coincidence that the June 2004 and the August 2004 Regents exams have not a single question about this lab (the other 3 required labs are represented in the questions). Sadly, I can think of some ways that it might have worked better, but teachers are warned to do the labs exactly as they are written or else the students may be disadvantaged by the way the questions on the exams might be worded.

Student Blogs?

I haven't been able to get my student blogs off the ground yet. There are two issues to consider. First, I need to have meaningful assignments that I can put up on a regular basis. This requires a considerable effort in terms of time and ingenuity. It isn't that easy to come up with ideas that actually require a blog and couldn't be done more easily in another format. Obviously there are things I want students to view on the internet at some point in time, but we haven't got there yet and assigning students to view content on the internet in and of itself doesn't require a blog response. The central challenge is to use blogs to foster strudent communication & collaboration. I may need to re-think my original model and go toward a voluntary blog assignment for now, allowing each student to set up his or her own personal blog. My original idea was to have a class blog and allow students mainly to respond to questions I post. That no longer seems a workable format, given already the time I spend planning and setting up labs and so on.

Secondly, there's the logistical matter of introducing students to the blog concept/format and training them in how to use it. This is actually easier if I allow students to have their own blogs. One problem with the original idea was that comments are uneditable, which gets to be a problem since I want students to work on grammar and spelling and the like.

In writing this post, the solution is becoming clearer. I will work on helping students set up their own blogs on a voluntary, extra credit basis. Then teach them how to use it, what it's purpose is, and allow them to submit certain types of homeworks in blog format. I'll think about how to encourage comments between students, and offer feedback as well. Stay tuned...

Student Conceptions: Origin of Species

Doing a search for ideas on teaching evolution with a constructivist approach, I happened upon this article by W.W. Cobern which makes the point that I alluded to in an earlier post on the importance of tapping into students existing conceptions of reality. I don't like to throw too much jargon around and frankly I don't have much of a memory for pedagogic gobbledygook. Nonetheless, the article reminded me of some of the constructivist principles that underpin my instincts and reminded me of the conceptual change model that's really the basis for my wanting to elicit students' current conceptions, and then present them with data or evidence that they must somehow account for. It's an interesting read, although some of the language and the constructivist bias can be a tad annoying.

And as I stated in the previous post, getting at students' ideas about the origin or origins of species necessarily involves a religious discussion. I jumped right into the discussion today with my 2 regents classes. I asked them to draw a diagram that showed in some way how the earth today came to have over 1.7 million different kinds of living things and to include a timeline. Most students struggled with how to represent their ideas visually. "God did it. How do I draw that?"

I should say that I did model what I meant by a diagram. I had read the word "asteroid" in a student's homework assignment, and elaborated on my own. Here is my model diagram and explanation:

It's a silly idea and a simple diagram, just to illustrate how one might take the idea that all the living things on earth arrived on asteroids from outer space and turn it into a visual representation. I got some interesting stuff, and I would like to post some of the student work, but I will have to get their permission first.

Not surprisingly, many students had a vague notion that god did it, but no understanding, not even a biblical understanding, of how or when that might have happened. A number of students opted not to diagram their religious understanding, which I of course gave them the freedom not to do. They instead diagrammed what they thought the scientific version of events was, and quickly added that they didn't believe it, it's just what scientists think. Needless to say, their diagrams of the scientific view were as sketchy as the religious diagrams.

Tonight's homework was to consider the fossil evidence that some millions of years ago, not one of the species of mammals that live today - giraffes, elephants, whales, humans, etc. - existed. How does your model (diagram) account for this information?

Introducing Evolution by Natural Selection

I'm slowly introducing some concepts to my students about evolution without actually mentioning evolution or natural selection. As I noted in an earlier post, I'm using mealworms as a springboard, of sorts. Today we discussed some differences and similarities between the mealworms we observed in class, and in the end I introduced the term "variation." We also discussed some of the more obvious variations among humans, but in my experience, students generally think of human variation as a special quality of humans - we are, after all, not "animals" in their view. For homework I am having students consider whether all this variation is such a good idea, from the point of view of the mealworms, or mightn't they be better off if they were all identical? I'm looking forward to the discussion in class.

What I am a little apprehensive about is the inevitable discussion of religious accounts of the origin of species. I like whenever possible to tap into students' prior knowledge or existing models of how the world works. But in eliciting prior knowledge about this particular subject, some religious conflict will be unavoidable. The fossil evidence particularly contradicts biblical accounts of creation, and students will have to find a way to deal with that conflict - either by rejecting the evidence (as many religious fundamentalists do) or by modifying their current models.

I will devote the next few posts to discussing how these conversations with students progress over the next couple of weeks.
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The other strand we are currently working on is using the mealworms to conduct controlled experiments. In both my regents classes, students are now reviewing experimental design by working on a simple problem question, testing a hypothesis about different foods and how they might affect the growth of the mealworms. Afterwards, students will continue observing and asking questions, which should eventually lead to more sophisticated and complex experiments. Students will have ample time to collect data over the course of the school year in conducting experiments that will relate in some way to one or more of our major themes in regents biology - living vs. nonliving things, homeostasis, ecology, heredity & genetics, reproduction & development, etc.