The other day I had a conversation with a student and a biology teacher about whether human chins have a purpose. Yes, chins. As in the outcropping of bone beneath your lower lip. That kind of chin.
Apparently, humans are the only animals to have a chin, according to this article which was sent to me by the teacher. In this article, it compares the evolution of chins to Spandrels in classical architecture. And since I totally tend to geek out on stuff that interests me, this sent me down a couple-hour-long rabbit hole reading where the idea of Spandrels came from and how they are applied to evolutionary biology, as well as some of the pushback against Spandrels as an analogy to evolution.
For a short and limited overview, here are wiki articles on the original use of the term Spandrel, and how Spandrel tends to be used as an explanatory device in Evolutionary Biology.
Originally, I thought the idea of the Spandrel was a neat way to conceive of evolutionary adaptations that defy explanation. But, to my surprise, the more I read about Spandrels the less convincing I find it. In fact, I found that I don’t like Spandrel explanations for the same kinds of reasons I don’t like "God of the Gaps" explanations.
If you don't know, "God of the Gaps" is a tactic used by some Religious Creationists to try and find a way to put God into the evolutionary process. It works like this: Every time an evolutionary problem gets too complex for easy explanation, God is invoked as the solution to "fill the gap" of knowledge. You can't figure out how eyes evolved? No problem! Just say God intervened in evolution to create the first animals with eyes. You can't figure out how wings evolved? Invoke God as the one who "bridges the gap" between reptiles and birds, creating the first winged animals. This is a clumsy and non-rigorous way to deal with both God and science.
So, I know comparing "Spandrels" to "God of the Gaps" at first sounds like an absurd comparison. But hear me out:
The God of the Gaps explanation is a kind of short cut for intellectual rigor: I cannot imagine how a certain gap of complexity can be filled by natural processes, so I will just say “God did it”.
The Spandrel explanation seems to be the same kind of reasoning, except in the opposite direction: I cannot imagine what kind of purpose or role this adaptation has, so I will just say “it doesn’t have a purpose or role”.
God of the Gaps argues from ignorance to purpose, while the Spandrel argues from ignorance to purposelessness. Neither seem compelling to me.
Just to take the architectural example that launched Stephen J Gould’s original use of the Spandrel metaphor in 1979: Spandrels can easily have a couple of architectural functions. First, a Spandrel may actually have a role in structural support, as in the Spandrels used in domes. Second, a Spandrel may be intentionally designed to trigger aesthetic pleasure through its decorative potential. Or to put it another way: Spandrels probably do not just happen, and then artists decide to decorate them. Rather Spandrels are designed for the purpose of decorating them. The biological use of the term seems similarly flawed. And this is not just my opinion. Other biologists have made similar criticisms of Spandrels as explanatory devices.
As a side note, biologist Richard Prum argues that there is a drive to value or aesthetic expression, alongside the drive to reproduce and propagate the genes, which together form the motor which drives evolution inexorably onward. He outlines this in his book “The Evolution of Beauty” (full disclosure, I’ve only heard him talk about the book; I haven’t read it yet).
If his hypothesis is even partially correct, it could mean that aesthetic adaptations are valuable and purposeful in their own right, without any recourse to reproductive or survival utility. And I will admit that part of me wants to believe this is true because I would love to believe that Beauty drives the development of the cosmos just as much as Survival drives the universe. It would mean that BOTH value AND fact are then needed as causal explanations for why things are the way they are.
If Beauty or Value is a driver for evolution, then Gould’s concept of Spandrels becomes highly questionable. And even if Survival is the only main driver for evolution, the Spandrel concept still seems to be more of an admission of ignorance of purpose rather than lack of purpose. (And throughout this I’m using purpose in the sense of a “function which enhances survival through natural selection” rather than some sort of designed purpose or divine purpose).
So this brings me back to chins: If chins are not a Spandrel, I’m going to guess they allow more complex mouth musculature, which in turn facilitates the development of more complex forms of verbal and nonverbal language, which in turn enhances human cooperation and planning, which in turn enhances human survivability. And it allows us to beat box.
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