MSU College of Natural Science Campus Theory Seminar
                  A SCIENCE AT THE EDGE SEMINAR

    
                     Friday, December 7, 2001
                      11:30 a.m. Room 224 PA
                 Refreshments served at 11:15 a.m.

                          Geoffrey West
                  Los Alamos National Laboratory

           The Tree of Life:  Universal Scaling Laws in 
    Biology from Molecules and Cells to Whales and Ecosystems

ABSTRACT

Life is the most complex physical system in the Universe manifesting an 
extraordinary diversity of form and function over an enormous scale 
ranging from the largest animals and plants to the smallest microbes. 
Yet, many of its most fundamental and complex phenomena scale with size 
in a surprisingly simple fashion. For example, metabolic rate
(the power needed to sustain life) scales as the 3/4-power of mass over 
27 orders of magnitude ranging from molecular and intra-cellular levels 
up through the smallest unicellular organisms to the largest animals 
and plants. Similarly, time-scales (such as lifespan and heart-rate)
and sizes (such as the radius of a tree trunk or the density of 
mitochondria) change with size with exponents which are typically 
simple powers of 1/4. The phenomenology of these "laws" will be reviewed
and a quantitative unified theory presented that can explain their 
origin, including that of the universal 1/4-power. 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 optimised by the forces of 
natural selection.  Integrated descriptions of the cardiovascular, 
respiratory and plant vascular systems will be presented as explicit 
examples. It will be shown how scaling universality can be related to 
an effective additional fourth spatial dimension of life. Extensions to
growth, aging and mortality, ecosystems and the nature of evolution, 
including the concept of a universal molecular clock, will be discussed.