Answer: Urethral Size To Bladder

Of all the golden ratios that could be uncovered in the animal kingdom, one is, rather ironically, literally golden. A group of physicists from Georgia Tech studying fluid dynamics applied their interest in the subject to zoology and discovered something quite interesting.

Mammals, regardless of their physical size, have evolved to have a very stable bladder to urethral size. In other words, whether you’re a mouse, a human, or an elephant, the diameter and length of your urethra is in direct and stable proportion with the size of your bladder. It appears that all mammals have adapted to be able to void their bladders in an average of 21 seconds.

Now, if you’re curious why a bunch of fluid dynamics oriented physicists would care about mammalian bladders, their interest hinges on the scalability of urinary systems and how those systems handle increasing waste volumes with the same efficiency regardless of scale. Information gleaned from studying how urinary systems scale between 100 pounds and a 1000 pounds could be used to improve human-constructed hydrodynamic systems.