A new paper by P. J. Yang et al. at ArXiv.org (reference and free download of the first page below) has produced a new Law of Biology. The whole paper isn’t online, and I don’t know where it was submitted, but. . . .well, the title speaks for itself:
And what is that duration, exactly? The abstract says about 21 ± 13 (is that the standard deviation among species?) seconds:
I don’t completely get this, but hey, it’s physics, Jake. How does simply lengthening the urethra increase the flow. What about its width? The penultimate sentence is ambiguous, perhaps smacking a bit of teleology, since a system can’t evolve for future contingencies, like being scaled up without hurting its function. But that may be some kind of shorthand.
A precis at Seriously, Science? on the Discover blogs just reiterates the paper, but adds a video showing micturation in mammals (you get a bonus defecation with the elephant), and then some geometry and algebra presented quickly, showing that the duration of urination increases only as the sixth root of body mass (mass^0.1666), i.e., very slowly, so that a large mammal will have pretty much the same duration as a small mammal. Maybe you physics buffs can figure it out from the quick presentation on this video:
If you understand their conclusion based on the geometry and algebra, please explain in a comment.
I eagerly await the publication of the full paper. In the meantime, I think we should all start timing ourselves.
Yang, P. J., J. C. Pham, J. Choo, and D. L. Hu. 2013. Law of Urination: all mammals empty their bladders over the same duration. submitted