Disney’s “Twelve basic principles of animation” outline the basic characteristics of good animation.

1. Squash and stretch
2. Anticipation
3. Staging
4. Straight ahead action and pose to pose
5. Follow through and overlapping action
6. Slow in and slow out
7. Arc
8. Secondary Action
9. Timing
10. Exaggeration
11. Solid drawing
12. Appeal

I think there are some parallels between animation and modelling biology, and I wonder how these twelve basic principles for ‘good’ animation are similar to ‘good’ models. (Note: ‘good’ is a function of the user/observer, and will change from person to person! Some people like CGI animation, others like the Lion King.)

I like models that distill a key feature of biology, usually representing a feature with a set of equations. For example, how interactions between organisms can be distilled to their shared use of resources (Resource Ratio Theory), or how nutrient uptake can be represented as an extension of enzyme kinetics (e.g., from Aksnes and Egge, 1991). Animations are similar, their goal isn’t to perfectly represent the actual humans or characters. One goal of animation is to highlight salient features, perhaps to ultimately triggering our emotions.

The same is true in models of biology. Models can be used to capture the salient features of a biological system. Instead of triggering our emotions, we can use models to clarify and quantify our understanding of a system. They will never capture all the details!

What can we learn from these twelve principles of animation, to improve mathematical models of biology? There are several categories of animation principles that I’ll try to distill.

1) Physics-based rules: Squash and stretch; Follow through; Arc; Secondary Action

“Squash and stretch” is a basic principle where objects squash once they hit another surface. The classic example / animation exercise is a ball dropping. “Arc” represents gravity – characters flying through the air should arc, rather than go along a single straight line. Aesthetically, animations missing these principles simply just look off. It’s hard to articulate precisely why, but comparing two animations without these basic attributes, I’ve found that there is a clear winner.

What are these basic principles that models in biology should adhere to? Some write that there are ‘first principles’ in biology – what are they? Why are they first, and not second? I’d argue that conservation of mass is a good place to start, and maybe also diffusion. I’m tempted to say that another basic principle is that all things are selfish, in an evolutionary sense. I’m not sure there are simplifying/unifying principles in biology, the way they exist in physics (or at least as I’ve heard they exist in physics!). I would love to hear what others think: which key features should models in biology adhere to?

2) Aesthetic-based rules: Solid drawing, Slow in and slow out, Anticipation

Should certain models be considered better because they are more aesthetic? What does it mean for a model to be more aesthetic? I’ve heard that in math, some people strongly prefer elegant or beautiful proofs (e.g., this paper). I think this is just unavoidable in some ways. A simpler model, that achieves the same thing as a more complicated model, might be considered more aesthetic (?). But if it’s simpler, by definition, it should be more interpretable. I don’t necessarily think a good model means it’s more aesthetic, but maybe there’s some correlation there.

At the risk of killing the potential connection between animation and modelling, I’ll stop the comparison here. Would love to hear others thoughts, if anyone ever reads this.