Tuesday, March 16, 2010

Nature Flows Downhill

A radical notion with deep implications for our understanding of the universe is now percolating within scientific circles—nature flows downhill.

You may recall learning about the second law of thermodynamics, the unwavering propensity of energy to disperse and, in doing so, transition from high quality to low quality forms—“increasing entropy,” to use the physicists' preferred term. High quality in this case refers to energy that can be put to use for a variety of purposes, whereas low quality energy generally refers to heat. Ecologist Eric Schneider (1) expresses the second law a little differently, arguing that "nature abhors a gradient," where a gradient is simply a difference over a distance—for example, in temperature or pressure. It helps me to think of this trend toward reducing gradients as nature flowing downhill. That is, if we think of a gradient as a more of something on one side and less of it on the other side, stuff tends to slide downhill from the more-side to the less-side.

In nature, open physical systems—including those of the atmosphere, hydrosphere, and geosphere—embody this law, being driven by the dispersal of energy, and particularly the flow of heat, “downhill” in the direction of some equilibrium state. Phenomena as diverse as the motions of lithospheric plates, the northward flow of the Gulf Stream, and occurrence of deadly hurricanes are all examples of this process at work.

Growing evidence suggests that life is no different. It’s often been said the life's complexity contravenes the second law (since organization is the opposite of chaos or entropy), indicating the work either of a deity or some unknown natural process, depending on one's bias. Yet the evolution of life and the dynamics of ecosystems strictly obey the second law, continually dissipating low quality energy. Living systems carry out the task not by burning brightly and disappearing, like a forest fire, but through stable metabolic cycles that store chemical energy and continually reduce the solar gradient (that is, the difference in available energy between the sun and the Earth).

Photosynthetic plants, bacteria, and algae capture energy from the sun and form the core of all food webs. So virtually all organisms, including us, are made of sunlight—temporary waypoints in the flow of energy. As energy goes from plants to herbivores, around 90% is lost to heat. This rampant dispersal of energy continues up the food chain when herbivores are consumed by carnivores, and again when carnivores fall prey to other carnivores. As a result, meat-eaters like orcas and lions must subsist on about 0.00001% (one hundred thousandth of one percent) of the energy originally captured by plants. This precipitous trend toward diminishing returns explains why ecosystems tend to have many more plants than herbivores, and many more herbivores than carnivores.

From the point of view of the food web, life appears extremely inefficient in delivering energy. But if the goal is to disperse energy, life is phenomenally successful.

Moving from ecology to evolution, life has become increasingly complex over the past 3.5 billion years, evolving from microscopic single-celled bacteria to macroscopic multicellular organisms of stunning diversity. Accompanying this bewildering increase in diversity has been a corresponding increase in biomass (the mass of living organisms). This dramatic transformation is not due simply to natural selection, as most evolutionists still argue, but also to nature's "efforts" to grab more and more of the sun's flow. The slow burn that characterizes life’s metabolism enables ecological systems to persist over deep time, changing in response to external and internal shake-ups.

Ecology has been summarized by the pithy statement, "energy flows, matter cycles." Yet this maxim applies equally to complex systems in the non-living world; indeed it literally unites the biosphere with the physical realm. More and more, it appears that complex, cycling, swirling systems of matter have a natural tendency to emerge in the face of energy gradients. This recurrent phenomenon may even have been the driving force behind life's origins. (For those interesting in the origin of life, I strongly recommend the following video [2]).

This idea that nature flows downhill is not new, and is certainly not mine. Nobel laureate Erwin Schrödinger was one of the first to articulate the hypothesis, as part of his famous "What is Life" lectures in Dublin in 1943 (3). More recently, Jeffrey Wicken (4), Harold Morowitz (5), Eric Schneider and others have taken this concept considerably further, buoyed by results from a range of studies, particularly within ecology. Schneider and Dorian Sagan provide an excellent summary of this hypothesis in their book, "Into the Cool" (1).

The concept of life as energy flow, once fully digested, is profound. Just as Darwin fundamentally connected humans to the non-human world, a thermodynamic perspective connects life inextricably to the non-living world. This radical idea, once broadly distributed and understood, is likely to provoke reaction from many sectors, including religion and science. The wondrous diversity and complexity of life through time, far from being the product of intelligent design, is a natural phenomenon intimately linked to the physical realm of energy flow.

Contrary to the current consensus among biologists, evolution is not driven by the machinations of selfish genes propagating themselves through countless millennia. Instead, ecology and evolution operate in tandem as a highly successful, extremely persistent means of reducing the gradient generated by our nearest star. In my view, evolutionary theory (the process, not the fact of evolution!) and biology generally are headed for a major overhaul once investigators fully comprehend the notion that the complex systems of earth, air, water, and life are not only interconnected, but interdependent, cycling matter in order to maintain the flow of energy. Nature—living and nonliving—flows downhill.

Outside the halls of science, seeing ourselves as inextricably embedded in these flows of matter and energy has great potential to help us reconnect to nature. Currently, we tend to view humanity as somehow apart from (and above) “nature.” Many commentators on sustainability (including myself) talk about our “relationship with nature.” But in many respects this is a twisted notion. We may as well speak of the human relationship with humanity, since we are part of nature in exactly the same way that we are part of humanity. Recognizing our bonds not just to other life forms but to the nonliving aspects of nature can go a long way toward bridging the human-nature divide.

References
1) Schneider, E. D. and D. Sagan. 2006. Into the Cool: Energy Flow, Thermodynamics, and Life. University of Chicago Press, Chicago.
2) Lecture by origin of life researcher Eric Smith: https://www.umail.utah.edu/owa/redir.aspx?C=bd6cc3778b064ad483adea8217d2542b&URL=http%3a%2f%2ffora.tv%2f2007%2f04%2f18%2fInevitable_Life
3) Schrödinger, E. 1944. What is Life: The Physical Aspect of the Living Cell. Cambridge University Press, Cambridge.
4) Wicken, J. 1987. Evolution, Thermodynamics, and Information: Extending the Darwinian Program. Oxford University Press, New York.
5) Morowitz, H. J. 2002. The Emergence of Everything: How the World Became Complex. Oxford University Press, New York.

(Note: This post is modified from a piece of mine that originally appeared on Edge.org in January, 2006.)

5 comments:

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