Sunday, February 24, 2013

Ecology for economists

Česká verze zde

This post is the second part of longer lecture, "Is God on our side? Economics at the borders of nature." The first part is here.

Ecology for economists

Let’s begin with a somewhat idealized image of a prairie ecosystem. The most obvious species is the bison, but the most important element is actually the grass.
We can illustrate the flow of energy from the grass (and other plants) to herbivores, and from them to carnivores, and then to decomposwers and to the soil, where it simply lies, or from where it goes back into new plants. And all the energy originally comes from the sun.

That is, all solar energy captured by the grass is either consumed by organisms in the system or is stored in the soil or in dead grass. And all the energy consumed or stored comes from the energy captured by the grass. This is a manifestation of the First Law of Thermodynamics, which we can express as: energy can neither be created nor destroyed, only transformed. In folksier language, There’s no free lunch!

We also see that the greatest amount of biomass is in grass, there’s less in insects and rodents, and less still in birds of prey. This happens because, at every level, energy is consumed by creatures’ metabolisms, and so there’s less left over for further levels. This is an expression of the Second Law of Thermodynamics, which says that every time energy is transformed, a significant piece of it dissipates and becomes unusable. In less formal terms, You can’t even break even!

We can simplify and generalize our ecosystem diagram like this:

It’s not shown there, but we can also talk about the functions of various elements of the ecosystem, from capturing solar energy to enriching the soil. And we see that matter mostly circulates, whereas energy passes through the system and drives it.

So much for the basics of the functioning of the ecosystem. What about change? What lies behind the formation of such structures.

Here we will allow ourselves a slightly anthropomorphized version of the 2nd Law, following the book Into the Cool, by Eric Schneider and Dorion Sagan.

In nature we see various structures that reduce thermodynamic gradients, for example heat convection in a pot, which reduces the difference between the warmth of the burner and the cold of the air.

Or even a hurricane, which reduces the gradient between the warmth of the ocean and the cool of the atmosphere.

It truly is a complex structure, with various typical elements.

And a hurricane really does reduce that gradient, as can be seen in the trail of cooler water in the wake of the hurricane.

These examples illustrate two principles.
  • First, structures like these exist only in the presence of sufficiently large gradients. Without a large temperature differences between the ocean and the atmosphere, there can’t be a hurricane.
  • Second, structures typically come into being that accelerate that reduction of gradients.
Figuratively, it’s as if the 2nd Law “wants” structures which effectively reduce these gradients.

Less figuratively, the 2nd Law “selects” structures which reduce gradients quickly and effectively. The way the selection works is that if a structure makes better use of local gradients, it grows and doesn’t leave room for other structures, and it reduces those gradients, so it doesn’t leave gradients for those other structures.

But this isn’t just about inanimate structures. Life also lives by the use of gradients, that is, by their reduction.

Such as when you digest food so you have energy for movement.

In contrast to inanimate structures, life is capable of actively seeking out and capturing gradients.

We can even imagine every living thing in terms of its relationship to gradients: Finding; capturing; utilizing.

Genetic mutations change at least one of those three aspects of our relationship to gradients.

A successful mutation is one which, in a given environment, improves the performance of an organism with regard to at least one of those three tasks.

For example,
  • sensitivity to light helps plants grow and helps worms move
  • cognitive abilities, so that you can gain more information from that light to which you are sensitive
  • a tendency to grow toward light
  • or a tendency to grow first toward the dark while on the ground, then toward the light once you encounter a tree
  • muscles, so you can move yourself in the direction of what your cognitive abilities take to be a useful gradient
  • warm-bloodedness, a strategy which allows you to function over a much broader range of environments—at a certain cost, of course
Another type of innovation is that which takes gradients that had been useless to a given organism and renders them accessible or useful, for instance:
  • detoxification
  • a cow’s digestive system
  • earlier, photosynthesis

Genes can encode not only such physical technologies of biological species, but also their behaviors. The journal Nature recently published new research results about the genetic basis of animal behavior (more here), say the form of a burrow of a rodent, or the tolerance of different ants for the presence of more than one queen in the colony. But these genetically coded behaviors also survive because they allow the organism to do better at finding, capturing, or consuming surrounding gradients.

In all of these examples we can see analogues of the selection principles in a market economy. In that context I spoke of diversity, differences in profitability, and the capability of spreading. In the case of biological evolution we have diversity, differences in the profitability of survival, and heritability of those differences. The selection of successful mutations happens through the joint operation of those three principles.

But this selection of more successful biological species obeys the same principles as does the selection of inanimate structures such as hurricanes. Because a more successful individual does a better job of finding, or capturing, or utilizing some gradient from its surroundings, that is, it accelerates the reduction of local gradients. We could say that successful mutations serve the 2nd Law’s desire for gradients to be reduced.

And it’s not just about individuals or about individual species, because there’s already agreement (at least among some scientists) about the concept of group selection. Prof. David Sloane Wilson writes about this effectively in his book Evolution for Everyone.

There have been objections that group selection contradicts the basic Darwinian process of survival of the fittest, because it’s not the group as a whole which reproduces, but rather the individuals in that group. But an individual in a well-functioning group may have an advantage over the most fit individual in a system made of parts that aren’t as well suited to each other. So selection doesn’t operate on the system as a whole, but it does operate on individuals in such a way that they become suitable components of the whole system.

In this way we get for example “superorganisms” such as termites, which build nests with incredibly subtle engineering. This isn’t a result of direct selection of the whole colony—consistent with Darwinian principles, what’s at work is selection of fit individuals. But the genes which make individuals better components of the whole also raise the fitness of the colony and at the same time the fitness of the individuals in it.

And we get the flocking behavior of birds. It's individual (pairs of) birds that reproduce, not the flock. But the flock itself is generated by relatively simple rules governing the behavior of each individual bird, rather than rules for the flock as a whole. So if an individual inherits behavior that results in flocking, it is part of a "fit" whole and so it is more likely to survive. Evolution selects for flocks by selecting individuals that function as part of the flock.

Similarly, we see coevolution. This is a natural result of the fact that an organism’s environment is created not just by such inanimate factors as average temperature or annual rainfall, but also other living species. When one species successfully evolves, it thereby also changes the environment for all other species, and when it’s their turn to evolve so as to better adapt to their changed environment, they once again change that very environment. And so individual species evolve together.

(Note that the cow’s stomach is a product of coevolution of the cow and the microorganisms that live in the stomach.)

This coevolution can involve not only the physical form of individuals but also mutally functional habits of animals.

And ecosystems are merely the logical extension of this phenomenon.

From inanimate structures effectively reducing gradients in their environment we progress to beginning forms of life, to cells, to multicellular plants and animals to the wonder of all the species and ecosystems that we see all around us.

The astonishing order and structure of groups of living beings arises automatically, repeatedly, almost inevitably.

And why doesn’t evolution favor species that are so fit at capturing gradients that they destroy ecosystems instead of building them up?

This does happen sometimes, but not for long, because such success is self-destructive. It’s true that an ecosystem itself is a gradient which can be captured, but if you capture too much, you undermine the ecosystem’s ability to supply you with gradients in the future. You weaken the ecosystem to the point that you can’t survive, and then the ecosystem either weakens further, or there arises some less destructive species that has a chance to survive.

So there is always pressure in the direction of more developed ecosystems, which do an ever better job of capturing solar energy and embodying it in the form of plants, and which use these gradients more effectively, passing them from one organism to another and on again, until the last drop dissipates into the cool of the universe.

From that perspective, ecosystems are predestined by the 2nd Law. Figuratively, we can say that they are expressions of the will of God.

Next: Economics as ecology

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