Are Cities Just Very Large Organisms?

By Sean Carroll | April 29, 2009 11:13 am

A couple of years ago I got to hear Geoffrey West, one of Time magazine’s 100 Most Influential People, give a talk on his research at a meeting of the American Association for the Advancement of Science. It was a fantastic talk, and I immediately had the idea to ask him to come to Caltech at some point and give it as a colloquium. So tomorrow he’ll be here, and anyone in the neighborhood interested in a semi-technical account of complex systems from physics to biology is welcome to stop by. He might be angling for the record for the longest talk title ever:

The Complexity, Simplicity, and Unity of Living Systems from Cells to Cities: A Physicist’s Search for Quantitative, Unified Theories of Biological and Social Structure and Organization

Although Life is very likely the most complex phenomenon in the Universe, many of it’s most fundamental and complex phenomena scale with size in a surprisingly simple fashion. For example, metabolic rate scales approximately as the 3/4-power of mass over 27 orders of magnitude from complex molecules up to the largest multicellular organisms. Similarly, time-scales (such as lifespans and growth-rates) and sizes (such as genome lengths, RNA densities, and tree heights) scale as power laws with exponents which are typically simple multiples of 1/4. The universality and simplicity of these relationships, together with emergent “universal” invariants, suggest that fundamental constraints underly much of the coarse-grained generic structure and organisation of living systems. It will be shown how these 1/4 power scaling laws follow from underlying principles embedded in the dynamical and geometrical structure of space-filling, fractal-like, hierarchical branching networks, presumed optimised by natural selection. These ideas lead to a general quantitative, predictive theory that potentially captures the essential features of many diverse biological systems. Examples will include vascular systems, growth, cancer, aging and mortality, sleep, cell size, genome lengths, and DNA nucleotide substitution rates. These ideas will be extended to social organisations: to what extent are cities or corporations an extension of biology? Are they “just” very large organisms? Analogous scaling laws reflecting underlying social network structure point to general principles of organization common to all cities, but, counter to biological systems, the pace of social life systematically increases with size. This has dramatic implications for growth, development and particularly for sustainability: innovation and wealth creation that fuel social systems, if left unchecked, potentially sow the seeds for their inevitable collapse.

We’ve talked before about the difficulty in defining “life,” although one safe criterion is that a living organism is going to be pretty complex. What about the other way — when you have an undeniably complex system like a city or a university or a galaxy, at what point does it become useful to think of it as a “living organism”? Those are hard questions, but one angle is to investigate the similarities that complex systems demonstrate as they are manifested at different sizes. That’s the idea of “scaling laws” — measuring a feature common to a set of complicated systems (number of parts, speed of motion, etc.) and see how they change as a function of scale.

You might have imagined that complexity comes in a variety of completely different forms, and there would be no simple relationship that included viruses, house cats, and sprawling urban centers. But the data reveal a remarkable degree of regularity — many complex systems share certain basic features, just scaled up or down in ways appropriate to their size.

Here is one startling example: every living being on Earth gets about a billion heartbeats worth of lifespan. Larger organisms live longer, but their hearts (or other analogous rhythmic processes) beat more slowly. Use those heartbeats wisely!

The next challenge, of course, is to understand why. A few stabs have been taken in that direction using ideas about hierarchical networks of smaller systems — about which I shouldn’t say much, at least until I’ve heard the talk.

Those of you who can’t make it to LA on short notice can enjoy this video, or check out Blake Stacey’s live-blog of a previous talk.

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  • Adam A

    The idea of biological (and super-biological scaling) is very interesting. However, the ~1billion heartbeat assertion bothers me. The average human’s heart beats ~60 beats/min. That works about to be about a 95 year lifespan. That’s a believable number. The average horse’s heart beats ~35 beats/min. That works out to be about a 163 year life span. That’s nowhere near right. A very old horse might live into its thirties.

    I suppose it’s possible that I just pick an anomalous case, as I don’t know any other animals’ heart rates off hand.

  • Mike

    For a nice discussion of the 3/4 and 1/4 scaling laws, see this paper:

    West, G. B., J. H. Brown, and B. J. Enquist. 1999. The fourth dimension of life: fractal geometry and allometric scaling of organisms. Science 284: 1677-1679.

  • Larry Lamb

    A billion seconds is 31.7 years, not 95 years

  • http://backreaction.blogspot.com/ Bee

    Anybody could point me to a reference summarizing what’s in the recording? Sorry for being old-fashioned, but I vastly prefer reading.

  • Maywa

    West contributed an article to Seed about this topic:

    http://seedmagazine.com/content/article/urban_paradox/

  • Adam A

    Oops, thanks Larry. That actually makes it worse. Human generally get a lot more than 32 years, and horses get a lot less than 56.

  • http://www.youth.neag.org Tobydyd

    A billion heartbeats. I find it very interesting that we all will reach that point, generally speaking, if we live our lives to their fullest. It makes me think of automobiles, and how each one will have certain things to change out at about the same mileage. The reason why – they were designed that way. Hearing about the similarities in organisms makes me think that there might be a designer behind it, a sign of a master design in place

  • http://www.lightfield.com William Croft

    This sounds aligned with what Hartmut Müller’s Global Scaling Theory is talking about. http://www.global-scaling-institute.de/26-1-Theory.html

  • CoffeeCupContrails

    Edward Purcell: Another physicist meddling in biology, with incredible insight and potential applications in engineering 30 years later.

    http://jilawww.colorado.edu/perkinsgroup/Purcell_life_at_low_reynolds_number.pdf

  • http://craigoverend.com/ Craig Overend
  • http://mengbomin.wordpress.com/ Meng Bomin

    Adam A:

    Oops, thanks Larry. That actually makes it worse. Human generally get a lot more than 32 years, and horses get a lot less than 56.

    It’s not that bad…neither is off by an order of magnitude, and if you consider how much medical advances and current comfortable lifestyles have contributed to the average human lifespan, 32 years really isn’t that far off.

    Tobydyd:

    A billion heartbeats. I find it very interesting that we all will reach that point, generally speaking, if we live our lives to their fullest. It makes me think of automobiles, and how each one will have certain things to change out at about the same mileage. The reason why – they were designed that way. Hearing about the similarities in organisms makes me think that there might be a designer behind it, a sign of a master design in place

    Ooh, an Intelligent Design troll. It’s very weak evidence if considered to be evidence at all. It fits very well with natural selection…as larger organisms require a longer period of time to reach reproductive maturity…thus greater selection pressure for longer lifetimes. Try again when you have something more interesting to say.

  • Metre

    I’ve often thought that the rate at which the heart beats sets the mental impression for the rate at which time passes. Even though a mouse lives maybe two years (if he doesn’t get eaten), he gets about the same number of heartbeats that we do – so his life seems as long to him as ours does to us.

  • jackd

    West should borrow the title of Samuel Delaney’s never-to-be-written novel, The Splendor and Misery of Bodies, of Cities.

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  • PTM

    [quote]It’s not that bad…neither is off by an order of magnitude, and if you consider how much medical advances and current comfortable lifestyles have contributed to the average human lifespan, 32 years really isn’t that far off.[/quote]

    The errors are bad: -54% for humans (average 70) +86% for horses (average 30).

    You can say that all organisms with heart live exactly 10 years and you won’t make an error of one order of magnitude for the vast majority of them.

  • Gavin Flower

    # Tobydyd Says:
    April 29th, 2009 at 4:19 pm

    […]
    Hearing about the similarities in organisms makes me think that there might be a designer behind it
    […]

    The basic problem with postulating a master “Designer” who is responsible for the complexity of life and its similarities – is that the logic used to justify there being such a designer, requires the designer to be designed by yet a greater being! Whereas, Evolution provides a much simpler answer as to why there are so many similarities, and how complicated organisms arose.

    Hence, suggesting a “God” designed everything is is self contradictory. This is usually glossed over by saying that “God” is beyond “space & time” or that it is “too complicated for mere mortals to fathom”. One could use the same logic to say the Universe always existed in one for or another, and that it is beyond our comprehension to ever understand – without having the complication of postulating a “God”.

    Perhaps, space & time no more have a beginning, than there is anything North of the North Pole! I am not saying that is a “satisfactory answer”, but reality may not be what we would like it to be. If someone says that the Universe has a beginning, we want to know what happened before – if someone says the Universe always existed, then we are not happy it had a beginning.

    Note that the Universe may be finite yet unbounded, just as the Earth’s surface is finite yet unbounded (restricting ourselves to 2 dimensions).

  • Gavin Flower

    “- if someone says the Universe always existed, then we are not happy it had a beginning.”

    should be:

    “- if someone says the Universe always existed, then we are not happy it had no beginning.”

    Sorry!

  • lluis

    This theory has been long ago published, explained and developed in International Systems Sciences congresses, here is a good article on my conferences on a theory of super-organisms based in the extension of non-euclidean geometries to the description of the morphological elements of those superorganisms, food for thought

    http://journals.isss.org/index.php/proceedings50th/article/view/29/200

  • lluis

    pd. regarding George west with whom i had a long talk at Sonoma’s 50th anniversay of ISSS, i believe his approach relies excessively in mathematics and power laws, without fully attack the conceptual changes of paradigm from mechanism to organism that are required to fully grasp this theory, that is why his team on the view of some of us, has not advanced much in the past decade… though in the 90s he made some interesting discoveries

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Cosmic Variance

Random samplings from a universe of ideas.

About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .

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