We’re doing it again: we’re offering our workshop, Changes in Nature, to interested teachers this summer, 11-15 July. It was fun and we learned a lot last year, so it’s going to be even better this year. This is a workshop that focuses on helping teachers develop strategies to teach “controversial” topics, evolution and climate change, so there’s a bit of us lecturing at them, and a lot of discussion and listening to teachers, so we all win.
I’ve been keeping my eyes open for papers on teaching evolution for this purpose, and one that caught my attention is a recent article by Price and Perez, Beyond the Adaptationist Legacy: Updating Our Teaching to Include a Diversity of Evolutionary Mechanisms. This has been a hobby horse of mine for a while, that so many people turn to selection and only selection to explain biological phenomena, and it impoverishes the field. So I was happy, sort of, to see an attempt to describe the errors a lack of diversity of explanations leads students to. I’m not happy to see these errors — and I see them in my students, too — but identifying the problem is a first step to correcting it.
Here, for instance, is a table of recognized misconceptions. You don’t have any of these, of course…right?
| CI | Misconceptions about Natural Selection That Appear When Students Discuss Other Evolutionary Processes |
|---|---|
| Genetic drift | Genetic drift is natural selection/acclimation to the environment that results from a need to survive. |
| Genetic drift is not evolution because it does not lead to directional change that increases fitness. | |
| Natural selection is always the most powerful mechanism of evolution, and it is the primary agent of evolutionary change. | |
| Dominance | Dominant alleles always increase in frequency in a population. |
| Dominance is related to the selective advantage of an allele or allelic pair. | |
| Heterozygotes always have a selective advantage over other genotypes. | |
| Evo-devo | Natural selection is always the preferred explanation, even when students are prompted to invoke more appropriate evo-devo mechanisms. |
| Characteristics that are not used by the organism are lost because they are not used, not because of the loss of maintenance selection. | |
| Evolution proceeds through the inheritance of acquired characteristics (not including potentially legitimate examples such as the genetic assimilation of induced phenotypes, the assimilation of learned behaviors, or inheritance of epigenetic modifications). | |
| Evolutionary stasis occurs only when stabilizing or positive selection does not occur. | |
| Lack of understanding of population-level processes. For example, attributing evolutionary adaptation, the population-level process, to an individual. |
This paper also leads to some very useful concept inventories that will be helpful, and that I’ll need to steal from next time I teach introductory biology (I may also be taking over teaching our evolution course in a few years, and I’ll definitely use them then). You might be wondering how you assess understanding of concepts in evo-devo, so here’s a sample question:
That one is easy — you can even rule out a couple of the choices directly from the stated premises of the question. But the appeal of selection is a powerful force, and students still get it wrong.
Price & Perez have an important message for improving the teaching of evolution.
Students more thoroughly exposed to a diversity of evolutionary processes can use these additional contexts to understand evolution. This strategy may be particularly appropriate for students who are having the hardest time understanding a diversity of evolutionary processes (low- and mid-level performers). We propose that refocusing our teaching to more equally include a diversity of evolutionary processes could result in a better understanding of natural selection and a better understanding of all evolutionary processes.
Dang. Now you don’t have to sign up for our workshop, since you’ve already got one of my major messages. But there’ll be more! And you get to spend a week in delightful Morris, Minnesota, at a time when it’s not snowing!
The workshop is sponsored by the Howard Hughes Medical Institute (HHMI). The grant we received from them a few years ago has been driving some wonderful programs here at Morris.
Very good list of misconceptions. I am going to steal that centipede question. There are many more misconceptions, as you know (if complex organisms evolved from simpler organisms, why are there still simpler organisms, and so on). And you cannot teach genetic drift and the neutral theory enough. Its thru that that students start to really absorb the naturalistic foundation of evolution. But even students who accept evolution will tend to drift into Lamarckian thoughts about how it works, and I find that I have to repeat the lesson of how natural selection works in the short term before they finally start to really get it. Here is a sample question (it comes with a series of annotated drawings, but you can picture it).
In the 1st drawing there is flask of growing bacteria. In the 2nd, an antibiotic is added. In the 3rd the bacteria population is seen to crash. Antibiotic resistant bacteria grow in the 4th flask. The question is: Which flask(s) have any resistant bacteria?
Without knowing anything about the centipede genome, it seems like B and C could be equally probable, although C probably less likely because it’s less likely that a single gene manages leg number. But I’m not sure how either B or C could be ruled out–can someone help me?
We would not expect something as simplistic as a “leg number gene” — that gets into another fallacy, that genes have single discrete functions. They often don’t.
From the observation I expect segments grow from one core segment, then a segment grows on each end of the original, and each one can grow another segment on the open end. So you start with one, then three, then five, etc.
To get an even number of segments out of that you need to stop growing segments at one end but grow one more segment at the other end.
I don’t understand why it wouldn’t happen though: at some point, the two ends get differentiated somehow. That differentiation a priori doesn’t seem like it would bar one end from growing an extra segment. So why couldn’t there be a gene that keeps the signal active longer (or shorter) on one end than the other?
Very interesting hypothesis, but no. I’m pretty sure the segments grow (or differentiate) head first.
I think the best question I ever asked undergraduates, in trying to understand what they had learned about evolution, was what they would do if they wanted to stop evolution (example was they were in charge of managing a recovery breeding program for an endangered species and needed to minimize domestication selection, genetic drift, and other change prior to releasing population back to the wild).
Well blow me down- I never knew that centipedes NEVER have a hundred legs. Added to my stock of not- dreadfully- useful factlets. Millipedes? Do they have a thousand (Wikipedia say no)?
But slightly more seriously, is it surprising that non- experts get confused when people use phrases expressing intention, like “evolutionary strategy”?
@7, Yup, this is exactly why appealing to etymology is a mistake in entomology is a bad idea.
(In general too, I just thought using two often confused words sounded more comedic.)
Right… I took AP biology in high school about 20 years ago, let me give this a try!
A) “… they choose to have …” organisms do not choose how to evolve, I remember my teacher warning me about this one!
B) Sounds plausible, although I don’t know why the mechanism of development would prefer odd numbers of pairs.
C) An odd/even gene sounds weirdly specific. However it’s mentioned that it’s possible to manipulate leg bearing number. I’m guessing this is either done by scissors, genetically, or by some bio-trick unknown to me.
D) This contradicts the statement that even and odd pairs have equal survival rates.
So I’d have to guess between B and C, and with C the “scissors” option sounds more plausible than some hypothetical very specific gene which is claimed has no benefit. I choose B!
The real definition of evo-devo:
https://m.youtube.com/watch?v=hRguZr0xCOc
Sorry. Couldn’t resist.
cvoinescu@5: well there goes that just-so story. Which I had just about rejected by the end of my post :)
robert79@9: presumably by applying just the right hormone at just the right time?
There’s one thing about the centipede thing that bothers me. Is there something about having an even number of body segments that doesn’t evolve naturally but can be produced by genetic alteration?
@12, That’s a good reason to rule out C. There are other ways to modify organisms that don’t involve genetic alterations.