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Frontiers in Science Public Lecture Series
The Complexity, Simplicity, and Unity of Living Systems
Geoffrey B. West
Elementary Particles and Field Theory Group
Life is surely the most complex physical system in the Universe. Understanding
the enormous complexity of even the simplest organism is beyond the
reach of present-day science. The origins, structures, dynamics and
organisation of life ranging from molecules to ecosystems will remain
a major ongoing challenge throughout this century requiring close collaboration
across all sciences. Though based on the same fundamental physics and
chemistry, Life manifests an extraordinary diversity of forms, functions
and behaviours ranging over an enormous scale: the largest animals
(whales) and plants (sequoias) weigh a remarkable billion trillion
times more than the smallest microbes (mycoplasma). In spite of all
of this, many of life's most fundamental and seemingly most complex
phenomena scale with size in a surprisingly simple fashion. For example,
metabolic rate (the power needed to sustain life - the approximately
2000 food calories you require per day), lifespan (your allotted "three
score and ten years"), and growth rates (the 20 years you took to reach
adulthood) all change in a remarkably simple fashion over this immense
spectrum of biological size. Furthermore, these scaling laws exhibit
a universal mathematical behaviour reflecting fundamental unifying
principles that have crafted and constrained the way life functions
and is organised from Molecules and Cells to Whales and Ecosystems.
The basic idea to be explored in this lecture is that, driven by natural
selection, life at all scales is sustained by hierarchical fractal-like
branching network systems whose universal characteristics determine
many of the generic properties of living organisms. Functionally, biological
systems are ultimately limited by the rates at which energy, materials
and information can be supplied through these networks. Examples include
the macroscopic cardiovascular, respiratory and neural systems of mammals,
the interconnectedness of an ecosystem, trees and plants, and the microscopic
pathways within intra-cellular mitochondria. This paradigm will be
explored and developed as a way of viewing many phenomena where hierarchical
structures have evolved. Examples will include speculations concerning
Growth, Aging and Mortality, Sleep, Genome Size, and Cities and Corporate
Structures.
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