Physicists and engineers decide how to analyze evolution

A big story in the press today. Scientists – mechanical engineers and physicists, one working for Boeing with his office only a few miles from my home – show that the evolution of airplanes works the same way as the evolution of organisms:

The evolution of airplanes

A. Bejan, J. D. Charles and S. Lorente

J. Appl. Phys. 116, 044901 (2014);

(fortunately this paper can be downloaded for free).

They make allometric plots of features of new airplane models, log-log plots over many orders of magnitude. The airplanes show allometry: did you know that a 20-foot-long airplane won’t have 100-foot-long wings? That you need more fuel to carry a bigger load?

But permit me a curmudgeonly point: This paper would have been rejected in any evolutionary biology journal. Most of its central citations to biological allometry are to 1980s papers on allometry that failed to take the the phylogeny of the organisms into account. The points plotted in those old papers are thus not independently sampled, a requirement of the statistics used. (More precisely, their error residuals are correlated).

Furthermore, cultural artifacts such as airplanes do not necessarily have a phylogeny, as they can borrow features from each other in massive “horizontal meme transfer”. In either case, phylogeny or genealogical network, statistical analysis requires us to understand whether the points plotted are independent.

The paper has impressive graphs that seem to show trends. But looking more closely we notice that neither axis is actually time. If I interpreted the graphs as trends, I would conclude that birds are getting bigger and bigger, and that nobody is introducing new models of small airplanes.

At least we may rejoice that the authors are not overly shy. They make dramatic statements on the implications for biology:

The engine mass is proportional to the body size: this scaling is analogous to animal design, where the mass of the motive organs (muscle, heart, lung) is proportional to the body size. Large or small, airplanes exhibit a proportionality between wing span and fuselage length, and between fuel load and body size. The animal-design counterparts of these features are evident. The view that emerges is that the evolution phenomenon is broader than biological evolution. The evolution of technology, river basins, and animal design is one phenomenon, and it belongs in physics.


Evolution means a flow organization (design) that changes over time.

Thanks, now I finally know what evolution is. And that biologists should go home and leave its study to the physicists and engineers.

[Note: I will pa-troll the comments as aggressively as I can and send trolling and troll-chasing to the Bathroom Wall.]