The Tree of Life: The Origin of the Universal Scaling Laws in Biology from Molecules and Cells to Whales
Geoffrey B. West
Santa Fe Institute and Los Alamos National Laboratory
Even though biological systems are the most complex physical systems known, they satisfy remarkably simple universal scaling laws. For example, metabolic rate (the power needed to sustain life) scales like the 3/4-power of mass over 27 orders of magnitude ranging from molecular and mitochondrial levels through the smallest unicellular organisms to the largest animals and plants. The phenomenology of these "laws" will be reviewed and a quantitative, unified model that can explain their origin will be presented. It is based on the fundamental observation that, regardless of size, almost all life is sustained, and ultimately constrained, by space-filling, fractal-like hierarchical branching networks which are optimized. Detailed quantitative, integrated descriptions of the cardiovascular, respiratory and plant vascular systems will be presented as explicit examples.