Features: July 2001
Yeah, but what about the crayfish?
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Geoffrey West has developed a theory that can explain scaling
laws in animals and plants. He tells Edwin Cartlidge that more of
his fellow physicists ought to consider devoting their talents to
understanding the biological world.
Geoffrey West has a mission: to put some "quantitative meat" into
the principle of natural selection. He believes that physicists
whom he says possess "the most powerful way of thinking about
the universe" should divert some of their attention from the
inanimate world and unravel the most fundamental problems:
consciousness, and the origin and nature of life. He's made a start,
having come up with a theory to explain the "quarter power" scaling
laws seen throughout nature. But he thinks there is plenty more to
do and is working feverishly on trying to quantify as much as he can
about the living world.
"Physics so far has concerned itself with the relatively
uninteresting stuff in the universe," he says. "My view is having
done that you now return to the problem that started these inquiries
in the first place, namely where did we come from and what is going
on inside our heads?"
It has been known since the 1930s that there is a well defined
relationship between the mass of a species and its rate of
metabolism. The metabolic rate of a species is proportional to its
mass raised to the power of three-quarters. This is just one of many
scaling relationships that involve a quarter or three-quarter power
and it holds true all the way from micro-organisms to blue whales.
In fact, West has found that it even applies to the mitochondria
West, who is based at the Los Alamos National Laboratory and the
Santa Fe Institute in the US, has come up with a mathematical theory
that can explain these remarkable empirical findings. Ultimately,
West would like to see the whole of evolutionary theory quantified.
He believes that up till now too much emphasis has been placed on
genetic algorithms, and that in a literal sense the theory has no
flesh and bones.
Making the move
West's move into biology was part design and part luck. He'd been
thinking in general terms about how to put the biological sciences
on a more mathematical footing and was teaching biological examples
of scaling laws to students struggling with maths. Then he got a
phone call from a distinguished ecologist called Jim Brown from the
University of New Mexico in Albuquerque. As a particle physicist,
West had been working with scaling laws for many years and was
recommended to Brown by a mutual acquaintance in Santa Fe. West got
together with Brown and his research student Brian Enquist, and thus
was born a highly productive interdisciplinary scientific team.
At first West looked upon his work on scaling in biology as
little more than a hobby and did not really believe he could make
any worthwhile contributions. But as he explored the literature it
became clear that there was a lot of quantitative data that were
very open to physics thinking, and that all the work that had been
done on these data so far by biologists was, he says, mediocre.
The problem that really fascinated West was ageing. The lifetime
of a species increases as mass to the one quarter and heart rate
decreases as mass to the one quarter. Therefore the total number of
heart beats, he realized, is the same across all species (within a
particular group of species, such as mammals). "The scaling laws for
mortality fit in with the scaling laws for living," he says. "I
realized that to come to grips with ageing and mortality you'd first
better understand how living things are sustained."
West, Brown and Enquist wrestled with the idea that the scaling
laws may be related to the structure and hydrodynamics of the
networks that supply nutrients to the cells in an animal's body.
After a year of intense activity, the trio discovered that scaling
results from the fractal-like structure of the network. They came up
with three fiendishly simple universal postulates, grounded in the
principle of natural selection, from which the scaling laws can be
deduced mathematically. The first of these was that the network
fills the whole of an organism's body. The second was that the
diameter of the smallest branches in the network does not vary from
one species to another since cell size is about the same in all
species. And the third was that fluid flows throughout the network
with minimum energy loss.
A different mind set
The work has drawn praise from many biologists, including the
popular science writer and Oxford professor Richard Dawkins, who
describes it as "a theory of enormous power, explaining a huge range
of facts with great economy".
West says that while many referees reviewing his work have also
been highly supportive, some have taken the opposite view. "You get
some referees' reports back that say our work is fantastic, the
greatest thing that they've ever read. Others say that it's horse
shit and that everything is derived from molecular biochemistry. And
then there's the classic, 'yeah, but what about the crayfish'."
"In general," he says, "although this was not true of my
collaborators, biology tends to be dominated by a certain type of
person in the opposite way to physics. They are always looking at
the particular, and everything is an exception." He says he does not
understand how such people can work in science if they do not
believe there are such things as universal laws. "If you had
biologists working, for example, in nuclear physics you would have
someone working on deuterium and then someone else working on helium
and they would not realize they were working in the same field."
West is, however, also critical of physicists. "As I've branched
out I've become aware about how conservative many physics
departments are. There are very well defined groups and each group
wants to maintain its own research strength and is often reluctant
even to look to other groups in the same department." Coupled with
the pejorative and arrogant view that physicists sometimes have of
other scientific disciplines, he thinks this will hold physics back.
"Because physics deals with fundamental problems at all scales that
are open to quantitative analysis, it should be reaching out to
other subjects like biology where there are important basic problems
to be solved. Some departments have moved gingerly in that direction
but they are always concerned with the deadly question, 'is it
West moved out of particle physics when he realized that there
was a widening gulf between theory and experiment. "Since the Large
Hadron Collider at CERN will not come on line until 2006, there will
have been a long, dry period of 10 years or more when there have
been no major new results from accelerators. And this may continue
if the scales relevant for unification are way beyond the scales at
which you can do experiments. High-energy physics cannot survive
like that. In fact, I've been surprised that more people from the
field haven't moved into other things."
West certainly has no regrets about his change of scientific
direction. "There's no question that the interface between physics
and biology is going to be a major area of investigation," he says.
"I think that some of the big problems in biology will only be
cracked once researchers start to nurture this interface more."
Dawkins also believes that physicists can make and have
made important contributions to biology. But he adds: "Not all
of them appreciate that biologists too have something to contribute
to biology. Geoffrey West does."
"Interdisciplinary research is an awfully difficult process,"
explains West. "It is extremely important that physicists do not
just say, oh this looks interesting and work on their own thing. I
think you have to be involved in a collaboration at an intense level
in a committed way, which is like a marriage. But not a marriage of
2001, a marriage of 1901. You go in with the attitude that divorce
is a very unlikely thing."
There looks to be no divorce on the horizon as far as West and
his collaborators are concerned. In fact, their relationship is in
rude health, with several papers lined up for publication. Not
content with single organisms, the group is extending its
mathematical description of nature to complete ecosystems and it has
been sharpening its knives for a major assault on natural selection
with a thermodynamic description of evolution.
Ultimately, West hopes that by combining their theory with
genetics and studies of the brain, it may be possible to integrate
the neural system and genetic code with the body's resource
networks. West calls these his "night thoughts", the ideas he turns
over in his mind late at night when there's nothing good on
television. But he believes and hopes that the study of living
things will one day be part of physics.
"You could imagine that physics departments of the very distant
future might have a sub-department of life and consciousness," he
says. "50 years ago one might have thought that it was not possible
to have a unified theory that explained the laws of the elementary
particles and the evolution of the universe. So it's not entirely
crazy to think that there might not be a credible theory that
explains life and consciousness."
Edwin Cartlidge is News Editor of
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