Why endothermy should be an explicit part of the biology curriculum in lower secondary.
Updated: Sep 14, 2020
During my training year I had to teach a Year 8 class the physics topic of heat. I had to hand a concept cartoon depicting a common question: What will happen if I put a coat on a snowman? The question is an interesting one and the students struggled. In fact, after speaking to many teachers, I discovered that is common difficulty, often due to the misconception of the coat giving heat to the wearer. After some thought (through a biology lens) I realised it may because students have little idea about endothermy.
Students have little awareness of the heat generation inside their cells. To them, when the weather is cold their bodies get cold. It's obvious because they can feel it. Of course, the fluctuation around the set point at which the body maintains itself is minimal, but as an adaptation, the senses are receptive to small differences, and the information is amplified to a feeling of discomfort.
Ok, but should we teach endothermy just so the physicists get to use the snowman cartoon? No, we should teach it because it helps students make sense of many biological phenomena, and as far as I am aware, it is not a common feature of biology curricula in the UK. It helps explain aspects of biogeography, animal behaviour, and morphology, both easily accessible and observable by students, which can all be unified under the concept of energy flow. Here's a few questions that relate to endothermy: Why is it that some large reptiles are able to eat one meal (a large mammal usually) per year?
Why is that humans have to eat so much energy dense food?
Why are we noticeably less hungry during hot summers?
Why do mammals and birds have feathers, but reptiles and amphibians appear naked?
Why can we find mammals and birds in really cold regions but less reptiles and amphibians?
Why do reptiles bask in the sun, where they are quite vulnerable to predation?
Why can some mammals and birds be active for hours, whereas reptiles and amphibians are quite sedentary?
Why does everyone keep talking about eating insects instead of mammals?
Why do mammalian predators always out-compete reptilian predators for the same niche?
But why are me more likely to find reptiles than mammals on oceanic islands?
So that's just a short list of common phenomena. But we also teach several things in the curriculum that rely on knowledge of endothermy for their full appreciation, such as thermoregulation, and it links so well with kinetic theory in chemistry, the behaviour of particles and rates of reaction. Teaching endothermy also functions as an excellent springboard for accessible discussion of variation, selection, adaptation, and the history of vertebrates. I begin in Year 7 with a story of how fish transitioned to land and the subsequent evolution of the amphibians, reptiles, birds, and mammals (opportunities for cladistics). The evolution of mammalian ancestors, as nocturnal and burrowing animals in the shadow of the tyrannic dinosaurs is a real hook, but it also sets up the narrative for the evolution of endothermy as a response to the environment in the mammalian lineage.
It can be used to look at arctic and desert mammals and introduce the biologist's favourite concept: the surface area to volume ratio. The conversation can include a consideration of humans, and by judging our morphology, in what type of environment students think we evolved compared to neanderthals. Here we could even talk about niche construction. The links seem endless, endothermy really does seem to offer an easy gateway to many of the unifying ideas in biology, energy and matter, evolution, organisation, homeostasis.
It's also possible that the evolution of endothermy was an important transition towards increasing complexity. Indeed, if we follow the second law of thermodynamics, organisms can only increase their order by exporting disorder in larger quantities, that is, we have become more complex, with our large brains, etc, only by dissipating more heat into our environment. Maybe endothermy was a prerequisite to human-like intelligence.
In summary, I think endothermy is a concept that allows students to make more sense of nature and their place in it, but is also a package full of opportunity for accessible discussion and practice of the big unifying ideas in biology that should satisfy biology teachers of all specialisms. Here, our chemist and physicist friends can find something of their liking too as the unifying concept is the flow of energy. If anything at all, it is a fantastic excuse to show some Attenborough clips from 'In cold blood: The cold blooded truth.'
Christian Moore Anderson
@CMooreAnderson (follow me on twitter)
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