Embedding natural selection throughout the biology curriculum
Updated: 6 days ago
In lower secondary science education, chemistry and physics curricula seem to focus on developing robust explanatory models, such as the particle model, and Newtonian forces. However, it often seems like many biology curricula are focus more on coverage of descriptive principles of life, such as the cell principle, the contents of cells, multicellular organisation, or 'functions of life'.
Secondary biology education should also be developing explanatory models of thinking that transcend the curriculum. It cannot be reduced to content coverage alone. I talk about one model, autopoiesis and flows of energy and matter here and here, but another that must be central to biology curricula is natural selection and patterns of evolution.
In my paper (summary here), I offer a framework (Figure 1. Below) for integrating the several facets of biology around the whole organism. At its simplest, this means integrating physiological and developmental systems with evolutionary and ecological thinking so they permeate the biology curriculum.
In this post:
I will provide examples of how natural selection can be an embedded component of the entire curriculum via frequent discussion and problem solving. Most teachers may wonder how discussion of natural selection can occur without just stating to students that the biological system being studied has been selected for in the past. Here are some ideas.
Figure 1. Copied from my paper: Putting nature back into secondary biology education: a framework for integration
Building a robust model
Before discussion and biological problem solving can take place, students must have, at least, a simple, but robust, mental model of natural selection.
However, most biology students spend (limited) time memorising (by rote in many cases) a detailed step by step process of natural selection observed at the surface level. As such, a large proportion of students leave secondary school without robust mental models of evolution (Nehm, 2018).
Here's an example of the steps student typically learn:
Reproduction leads to overproduction of offspring
Offspring inherit traits/alleles but with some variation
Variation is created by random mutations
The environment causes competition between organisms and a struggle for survival
Some offspring have traits that are better adapted to the environment
More adapted organisms are more likely to survive and reproduce
Next generation of organisms inherit the traits/alleles of those that reproduce
While it may seem like these steps are not tied to a concrete example, they are surface level steps that lack theory and abstraction. If we want students to form robust models of evolution then we need to be constantly oscillating between abstracted theory and concrete examples (on this oscillation see Maton, 2013, Maton 2014, and Kinchin et al., 2020).
What is the necessary abstraction?
The (abstracted) core principles found in all examples of natural selection can be organised into a hierarchy of the most important concepts: Variation, Selection, and Inheritance, and their subordinate concepts. The word diagram below (Figure 2) is one I've made to show this point both here, and to live draw to students in lessons when needed.
Figure 2. A flow-spray word diagram showing the hierarchical relationship between the concepts in the process of natural selection. By Christian Moore-Anderson
By teaching students these core concepts in this manner we get three advantages:
We have an abstracted hierarchical model for students to think with when viewing concrete examples.
It is much easier for students to remember several major steps and their subordinate concepts (hierarchically), than many small steps (linearly) (Reif, 2008).
We can update the subordinate concepts as students move through the biology curriculum and therefore steadily modify the complexity of the model. Thus, allowing natural selection to transcend the entire secondary curriculum
Additionally, once the core principles have been established they can be used as prompts for both answering written questions, and class discussions.
Where will teachers fit this into an overloaded curriculum?
It is understandable that teachers may not warm immediately to the idea of seemingly adding more to classes. However, it is not extra content, it is asking students to think deeply about the content already in the curriculum.
Embedding natural selection produces a positive feedback loop (Figure 3) on learning as the regular application of their mental model allows students to think more deeply about the content of lessons. And the this practice, and the feedback given, in turn, helps develop and strengthen the mental model.
Figure 3. A positive feedback loop when embedding natural selection in the curriculum
The better and more rapid the evolutionary way of thinking, the more deeply students can think about course content no matter the topic.
Building a robust mental model needs more than a couple of isolated topics
Students will need regular practice with scientific models so that they can become dominant over their intuitive, folk models (Evans & Rosengren, 2018). For example, such folk models in evolution include:
Essentialism: no within-population variation, and immutable species
Finalism: teleological belief, i.e. organisms evolve in order to..., that is not just paraphrasing
Lamarckism: Organismal agency over their own evolution, use & disuse, inheritance of acquired traits
A design principle
Such obstacles are unlikely to be surmounted by a handful of examples and a couple of well planned explanations, as good as they are. Purely folk, and purely scientific explanations are uncommon in secondary students. Rather, individual students can mix the two in varying proportions depending on the context, such varying species, and trait type (Nehm, 2018). Answering a couple of questions correctly will tell us little of their mental models of evolution. Students really do need embedded practice.
Ok, so, how can teachers embed natural selection easily and frequently?
Embedding natural selection: Trait spectrum cases
Here is how I would use the core principles as prompts for discussion of a trait. Beware, there are many evolutionary examples used in biology education that show a trait dichotomy, a variation of just two types. Research has found that some students form mental models of variation whereby all traits come in dichotomies (Alred et al., 2019). It is important therefore to use a trait spectrum.
To indicate a trait spectrum to students it can either be gestured or drawn. The whole procedure, which should be relatively quick (especially if embedded) is shown in Table 1 below.
Table 1. The procedure for discussing natural selection of traits
Let's say we're studying the digestive system. There are many traits of the intestine that we could choose to discuss but it's important to isolate them. For example, it could be the canonical villi, or microvilli. It could also be average transit speed, the extent of vascularisation, lumen diameter, or the extent of the mucous barrier, et cetera. In this case, let's keep it simple with the length of the intestinal tract and see how, in Table 2 (below), I could carry out a quick class discussion:
Table 2. An example of how I would discuss the trait spectrum case of intestinal length
Trade offs and correlations between two traits
In other cases, and at higher education stages, you may want to specifically look at two trait spectra. In this case a cross continuum is useful. Here's example (Figure 4) on the trade offs in life history traits (shorter to longer growth phases, and earlier to later onset of the reproductive phase). I have used this example to elicit response from students working pairs initially.
Figure 4. A crossed continuum of life history traits
Finally, very rich discussion can be had from comparing the systems of different species. To continue with our example of intestinal length, we could discuss why mammalian herbivores, carnivores, and omnivores have different lengths in their digestive tract. To learn more about this idea, read the summary blog post about my paper.
Christian Moore Anderson
@CMooreAnderson (follow me on twitter)
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Alred, A. R., Doherty, J. H., Hartley, L. M., Harris, C. B., & Dauer, J. M. 2019. Exploring student ideas about biological variation. International Journal of Science Education, 41(12), 1682–1700.
Evans, E, M., Rosengren, K., S. 2018. "Cognitive biases, or Cognitive bridges?" In Teaching biology in schools: Global research, issues, and trends, edited by K. Kampourakis and M. Reiss, 9-21. UK: Routledge.
Kinchin, I., N. Winstone, and E. Medland. 2020. “Considering the Concept of Recipience in Student Learning from a Modified Bernsteinian Perspective.” Studies in Higher Education 1–13. doi:10.1080/03075079.2020.1717459.
Maton, K., 2013. Making semantic waves: A key to cumulative knowledge-building. Linguistics & Education, 24(1), pp.8–23.
Maton, K., 2014. Knowledge and knowers: towards a realist sociology of education, Abingdon: Routledge.
Nehm, R. 2018. “Evolution.” In Teaching biology in schools: Global research, issues, and trends, edited by K. Kampourakis and M. Reiss, 164-177. UK: Routledge.
Reif, F. 2008. Applying cognitive science to education. Cambridge, US: MIT Press