10 June 2005
Bauer Center for Genomics Research
It has long been known that metabolic rate, heart rate, diameter of the aorta, and many other physiological properties scale in a systematic and inter-related way with body size. These scaling relationships hold over an astronomical range (~21 orders of magnitude) and across taxonomically diverse organisms. Moreover, these relationships are usually power laws with exponents that are simple multiples of 1/4. Over the past several years, a theory, originally proposed by West et al., has been developed to explain these relationships. This theory focuses on the cardiovascular system, about which it makes three assumptions: 1) the network is hierarchical and space-filling 2) the terminal units (capillaries) are invariant units, and 3) the energy to transport resources through the network--from the heart to the capillaries--has been minimized through natural selection. Using these three assumptions, I will derive predictions for the scaling of various properties of the cardiovascular system with body size and ultimately, for the mass dependence of metabolic rate. If time permits, I will discuss how these findings can be extended to study other interesting phenomena such as mammalian sleep times and cell size variation across species.
G. B. West, J. H. Brown and B. J. Enquist, "A general model for the origin of allometric scaling laws in biology", Science 276:122-6 1997. PubMed. PDF
V M Savage and G B West, "Biological scaling and physiological time: biomedical applications", in: T S Deisboeck, J Yasha Kresh and T B Kepler (editors), Complex Systems in Biomedicine, Kluwer Academic Publishing, New York, 2005. PDF
V M Savage, J F Gillooly, W H Woodruff, G B West, A Allen, B J Enquist and J H Brown, "The predominance of quarter-power scaling in biology", Functional Ecology 18:257-282 2004. Abstract
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