Explanation in biology is split between two big questions. These questions should inform how we teach, and the answers we expect from students. These questions are How? and Why? So what do these mean?—that idea started with Ernst Mayr.
In the 1960s Mayr published his ideas on the distinction between what he referred to as ultimate, and proximate causes in biology. Proximate causes are those events that occur just before an effect, for example, the titanic sunk because water rushed into a hole in its hull. However, the ultimate cause was the fact that it ran into an iceberg.
Mayr's distinction in biology went like this:
Ultimate causes of biological phenomena were explained by natural selection
Proximate causes were explained by physiology
Questions about ultimate causes often answer questions that begin with why. Whereas those about proximate causes often begin with how (Kampourakis & Niebert 2018).
Image by Christian Moore-Anderson & Blanca Martínez Valiente
Ariew (2003) suggested that Mayr's 'ultimate cause' idea wasn't satisfactory as it only referred to natural selection. He added in drift, gene flow, and mutation to these ultimate causes. Ariew describes these questions on evolution to be statistical questions, as they refer to why certain traits have become, and continue to be prevalent at the population level.
He prefers the term evolutionary causes or evolutionary explanations over Mayr's ultimate causes.
All other causes, Ariew suggests, are those that deal with mechanistic explanations of physiology. They are still proximate causes, but answer different questions, such as how? While developmental questions, such as 'How did it come about/be built?' are different to 'How does it work?' Ariew suggests that they both deal with describing a physiological mechanism within a biological system.
In my view, to get a rounded understanding of biological phenomena we need both an evolutionary view, and a mechanistic view.
How does this relate to the biology classroom?
If we want biology to be an explanatory subject then we should focus on improving our students ability to answer how and why questions.
All to often how students are asked to focus on the what and what for. If students just know the names of parts and what they do, they'll be left with descriptive knowledge alone. Sometimes, this is all there is time for. Fair enough. But for the core concepts of biology, we need to push our students further to understand how something comes about, and why it has evolved to be that way.
To help students further, we need to share these ideas with them. So they begin to understand the difference themselves between description and explanation in biology. As such, it may also be fruitful for teachers to make explicit when they are asking students and evolutionary why question, or a mechanistic how question.
This way, not only are students able to learn to explain biological phenomena, but we give them a tool for thinking about explanations. And this may then influence how they study biology in the future.
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References
Ariew, A., 2003. Ernst Mayr’s ‘ultimate/proximate’ distinction reconsidered and reconstructed. Biology and Philosophy, 18(4), pp.553–565.
Kampourakis, K., Niebert, K. 2018. Explanation in biology education. In K. Kampourakis, M. Reiss, ed. Teaching biology in schools: Global research, issues and trends. London: Springer, pp.236-248.