A argumentação de quem nega a responsabilidade humana no actual surto do aquecimento global - (posição negacionista fraca; a posição negacionista forte recusa mesmo esse aquecimento) - passa, em parte significativa, pela discussão da validade dos modelos usados pelos climatologistas, e pela contestação dos resultados deles retirados. Sobre a correcção disso estamos conversados.
Acontece, no entretanto, que os modelos são usados em outros ramos do saber - (penso que em todos, de modo explícito, ou implícito) - e a discussão sobre a sua validade, e sobre os pressupostos metodológicos que os conformam, acontece nos mais diversos contextos. Por exemplo, no das ligações que se podem estabelecer entre a economia e a biologia, quanto a metodologias, e a quadros conceptuais, que esta pode fornecer àquela. É o caso deste trabalho de Krugman: Economist's View: What Economists Can Learn from Evolutionary Theorists que aborda a existência de semelhanças metodológicas entre as abordagens da economia (neo-clássica) e da biologia evolutiva, e do papel que os modelos têm nisso - aliás, o que é dito tem implicações muito mais amplas, à luz do que se passa em termos de conjuntura, e da reflexão sobre os caminhos futuros da economia. Um excerto (parte final):
"Evolutionary theorists, even though they have a framework that fundamentally tells them that you cannot safely assume maximization-and-equilibrium, make use of maximization and equilibrium as modelling devices - as useful fictions about the world that allow them to cut through the complexities. And evolutionists have found these fictions so useful that they dominate analysis in evolution almost as completely as the same fictions dominate economic theory.
What is neoclassical economics?
I just said that these fictions dominate economics. But the question in economics is whether we understand that they are fictions, rather than deep-seated truths. For there, perhaps, is where economists have something to learn from evolutionists.
In economics we often use the term "neoclassical" either as a way to praise or to damn our opponents. Personally, I consider myself a proud neoclassicist. By this I clearly don't mean that I believe in perfect competition all the way. What I mean is that I prefer, when I can, to make sense of the world using models in which individuals maximize and the interaction of these individuals can be summarized by some concept of equilibrium. The reason I like that kind of model is not that I believe it to be literally true, but that I am intensely aware of the power of maximization-and-equilibrium to organize one's thinking - and I have seen the propensity of those who try to do economics without those organizing devices to produce sheer nonsense when they imagine they are freeing themselves from some confining orthodoxy.
That said, there are indeed economists who regard maximization and equilibrium as more than useful fictions. They regard them either as literal truths - which I find a bit hard to understand given the reality of daily experience - or as principles so central to economics that one dare not bend them even a little, no matter how useful it might seem to do so.
To be fair, there is some justification in the insistence of some economists on pushing very hard on the principles of equilibrium and in particular of maxmization. After all, people are smarter than genes. If I offer a model in which people seem to be passing up some opportunity for gain, you may justifiably ask me why they don't just take it. And unlike the case of genes, the argument that the alternative is quite different from what my imagined agent is currently doing is not necessarily a very good one: in the real world people do sometimes respond to opportunities by changing their behavior drastically. In biology purely local change is a sacred principle; in economics it has no comparable justification.
And yet I think that despite the differences, it would be better if economists were more self-aware - if they understood that their use of maximization-and-equilibrium, like that of evolutionary biologists, is a useful fiction rather than a principle to be defended at all costs. If we were more modest about what we think our modeling strategy is doing, we might free ourselves to accommodate more of the world in our analysis.
And so let me conclude this talk by giving two examples of how a more relaxed, "evolution"-style approach to economics might help us out.
Two economic examples
As you know, one of my areas of research has been the study of economic geography. Perhaps the most basic insight in these models has been the possibility of a cumulative process of agglomeration. Suppose that there are two regions, and one region starts with a slightly larger concentration of industry. This concentration of industry will provide larger markets and better sources of supply for producers than in the other region, perhaps inducing more producers to locate in that region, further reinforcing its advantage, and so on. It's a good story, and I am quite sure that in some sense it is correct. Yet when I and my students try to present this work, we often run into a surprising difficulty: theorists get very upset about the dynamics. Why, they ask, don't individuals correctly anticipate the future location of industry? How can you have such a model without forward-looking agents and rational expectations?
Now the fact is that when you try to do rational expectations in such models they become vastly more difficult, and the basic point becomes obscured. In short, here is a situation in which going all the way to full maximizing behavior - and trying to avoid the disequilibrium, evolutionary dynamics I assume - makes life harder, not easier. It seems to me, at least, that this is a situation where economists would do a better job if they understood that maximization is a metaphor to be used only to the extent that it helps understanding.
And when I run into this sort of critique I am envious of evolutionary theorists who do models like, say, the Fisher theory of runaway sexual selection, and can use myopic, disequilibrium dynamics without apology. (If you don't know that model, it works like this: suppose that there is one gene that makes peahens - that's the female of peacock - like males with big tails, and another that causes males to have big tails. If there is a preponderance of females that carries this gene, then males with big tails will have more offspring even if they have less chance of surviving because of their visibility to predators. But because a male with a big tail is likely to be the son of a female who likes big tails, this success will also tend to spread the gene for big-tail preference .... The resemblance to agglomeration is obvious- isn't it?).
Another issue: consider the question of whether and how monetary policy has real effects. In the end this comes down to whether prices are sticky in nominal terms. In my view there is overwhelming evidence that they are. But many economists reject such evidence on principle: a rational price-setter ought not to have money illusion, therefore it is bad economics to assume that they do. If neo-Keynesians like me suggest that a bit of bounded rationality would do the trick, the answer is that bounded rationality is too open-ended a concept, and can be used to rationalize too many different behaviors.
And yet in evolution the idea that there are limits to the precision of maximization is adopted cheerfully. When a bird sees a predator, it issues a warning cry that puts itself at risk but may save its neighbors; the reason this behavior "works", we believe, is that many of those neighbors are likely to be relatives, and thus the bird may enhance its "inclusive fitness". But why doesn't the bird issue a warning only its relatives can hear? Well, we just suppose that isn't possible.
In short, I believe that economics would be a more productive field if we learned something important from evolutionists: that models are metaphors, and that we should use them, not the other way around."
No entretanto, O Economist's View: "Alpha Markets" alerta para um artigo que refere o efectivo contributo que a teoria da evolução pode dar à economia, nomeadamente, na explicação dos incentivos dos intervenientes na actual crise financeira.
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