The trend I see in secondary biology education is that curricula put off evolution until a topic of genetics has been covered. In some cases this means that evolution and natural selection are not covered until Year 9, the third year of secondary biology, and is then not seen again until close to the end of Y11, the final year of compulsory secondary biology.
How can the most encompassing and uniting concept of the domain be give such little attention? How can it be that it has become dependent on the teaching of allele frequencies? While the model of natural selection we want students to have by the end of secondary education most definitely includes genetics and the random origin of mutations, there is a long road to run before we get to that point.
Below I give quick and rough argument (written while my son napped) in favour of not waiting for genetics to teach evolution, but this is far from exhaustive.
One argument against early evolution: Alleles are necessary knowledge
The main argument I have come across is that students need to know about alleles and random mutation to fully understand evolution by natural selection. This argument is especially supported by the idea that without understanding this concept, students may acquire the common misconception that variation is brought about in response to the environment, as if by the will of the organism. In other words, without knowledge of the origin of alleles, students will not correctly understand the concept of variation.
However, I disagree, but to really get to the bottom of this argument I will separate it into several points. Nevertheless, the overview is simply that understanding alleles is not necessary to make meaning of life on Earth.
Counter argument 1:
Darwin, Wallace, et al made sense of life without genetics
Until the formulation of the modern synthesis (mainly synonymous with neo Darwinism) evolution by natural selection did not require an understanding of genetics. In fact, the central thesis, lest we forget, of evolution is not genetics at all, but change. This was the big question of Darwin's time, the 'species problem' referred to whether species could change (transmutate, or transform as Lamarck put it). In a nut shell it was a question of whether species had an essence, or not. What Darwin and Wallace changed with their publication was to add a credible process that could lead to change and the origin of new species, and not just any change, one that was influenced by selection for specific traits.
Before the modern synthesis supporters of the theory of evolution by natural selection were able to make sense of the world by looking primarily at the traits of organisms. In fact, it is at this level that most people see the world, the level of the organism, not the molecular level.
Counter argument 2:
Developing a biologist's gaze: nothing makes sense except in the light of evolution.
Evolution by natural selection is a model for understanding the content of the entire biology course. Leave it till late (so to include genetics) impoverishes student understanding of topics that come before. It prevents the ample opportunities the curriculum provides to apply evolutionary thinking. By leaving evolution till late means that students get little practice with thinking like a biologist. This is a large enough argument for many books, but in summary, students will not develop the habits of mind of thinking like a biologist if its central overarching, unifying, explanatory theory, is reduced to two late topics in the secondary curriculum.
Counter argument 3:
Students do not need to learn the causal mechanisms of everything to understand.
Causal mechanisms are not the only form of explanation or understanding. Patterns too are explanatory and useful (Potochnik, 2017). In the same way that learning about acids, basis and the pH scale is useful (a pattern) without knowing the causal mechanisms of the reactions. So too is knowing that variation exists, is produced through sexual reproduction. This is quite intuitive for students when appealing to their knowledge of classmates and siblings. Knowing the causal mechanism for the origin of variation is not necessary to make sense of evolution. Students can do rather well knowing that variation exists, and comes about through inheritance via sexual reproduction (mixing of traits/DNA).
Counter argument 4:
Evolutionary models are as complex as the teacher makes them, but all are probably useful.
The GCSE exam mark schemes do not provide the ultimate model of natural selection, it is just a model of a certain complexity. Simplified models can be used with younger students (for example, without the details of genetics) and the model can increase in complexity over time. Once genetics has been studied, the model of natural selection can incorporate it.
Counter argument 5:
The genotype-phenotype relationship is a very difficult concept to understand.
Despite a few deleterious alleles resulting in well-known genetic disorders, we are far from understanding the causal complexity of phenotype. Just because alleles have been covered in the course, and are then put into a new evolutionary model, does not mean that they can truly make sense of what a change in allele frequencies really means.
Counter argument 6:
Misconceptions are inevitable, but leaving evolution till late will give you less time to find them.
Students still acquire the misconceptions about the origin or variation even with a genetics-first approach. It is not a fail safe sequence, and is unlikely to be any more successful than other sequences if students do not fully understand how genotype relates to phenotype. However, by waiting for genetics to begin teaching evolution, will inevitably give teachers less time to work with misconceptions. Especially important for biology teachers who leave evolution to one of their last topics in their GCSE course.
Counter argument 7:
Finally, and probably most importantly, evolution, including natural selection, appears in the final year of primary school education. Let's not leave that good work untouched. Let's pick it up in the first week of Year 7 biology.
Conclusions
Evolution is so central to understanding biology, it is central to making sense of our world. It can't be reduced to a late-coming topic with some mnemonics thrown in to help rote learn the process of natural selection.
Evolution cannot be reduced to just two (late) topics in secondary biology education. It's everywhere, so it's best to provide those simplified models early on, and build on them over time. You cannot build a disposition to think evolutionarily in two topics, but maybe you can through constant discussion and application of models through the entire secondary curriculum. To think like a biologist is a habit of mind, habits take time to acquire. If you've enjoyed this—check out my book. Download chapter 1 here—English edition—edición española—or check out my other posts.
Christian Moore-Anderson
@CMooreAnderson (twitter)
References
Potochnik, A., 2017. Idealization and the aims of science. Chicago: University of Chicago Press.