Why the bigger live longer and travel farther: animals, vehicles, rivers and the winds

Abstract

Here we show that constructal-law physics unifies the design of animate and inanimate movement by requiring that larger bodies move farther, and their movement on the landscape last longer. The life span of mammals must scale as the body mass (M) raised to the power 1/4, and the distance traveled during the lifetime must increase with body size. The same size effect on life span and distance traveled holds for the other flows that move mass on earth: atmospheric and oceanic jets and plumes, river basins, animals and human operated vehicles. The physics is the same for all flow systems on the landscape: the scaling rules of "design" are expressions of the natural tendency of all flow systems to generate designs that facilitate flow access. This natural tendency is the constructal law of design and evolution in nature. Larger bodies are more efficient movers of mass on the landscape.

Figure 1. Turbulent jets and plumes: the time averaged flow field occupies a cone with fixed angle.

Figure 2. The spreading of a river on an area is analogous to the spreading of a jet into a fluid reservoir (Fig. 1).

The upper image is the Okavango delta (NASA photo).

Figure 3. The spreading of the mass of vehicles and animals is completely analogous to the flow of water in river channels.