The Irrational Brain Hypothesis is among the most important hypotheses in science today, and it has been for decades.

You may disagree. You may argue that you have never even heard of it. Indeed, no one has ever heard of it. So how could an anonymous hypothesis be so important?

You probably have not heard discussion regarding the Human Intelligence Hypothesis either. Neither have I. It seems no one thinks it worthwhile to question the human belief in human intelligence. However, I once saw a car with a bumper sticker that read “What kind of intelligent species cooks itself to death?” Perhaps the freak who owned that car was aware of the HIH and wished to express skepticism. Or perhaps I mistakenly attributed rhetoric to a person who was just asking questions. In any case, the firm consensus is that humans are undoubtedly intelligent, and undoubtedly irrational as well. I do not recall any academic ever expressing doubt about either.

Unless I count the freak writing this, who sees humans as purely rational and remarkably intelligent. It takes quite a lot of intelligence to heat an entire planet as quickly as we have, even if unintentional or suicidal. It also takes rationality. The Tragedy of the Commons is tragically rational.

The Irrational Brain Hypothesis

The Irrational Brain Hypothesis is the hypothesis, almost universally assumed to be true, that humans, and brains/minds in general, are irrational. It is a foundational assumption for much of the research related to Bayesian Brain Theory, in which the conventional view is that the human brain has developed and evolved towards rationality. Thus a healthy adult brain in the twenty first century is said to “approximate rationality.”

What Does It Mean To Be “Approximately Rational?”

Perhaps this means that younger or less evolved brains believed 6+2 = 7, and then they developed or evolved to become brains that believed 6+2 = 7.9, which further developed or evolved to believe 6+2 = 7.99.  That would be progress of a sort (though not of the sort that provides much hope for the human condition).

I don’t think anyone really knows what “approximately rational” means. It does not take much thought to see that what is not rational is irrational.  I do not know what it could possibly mean for there to be a continuum of rationality/logic, and I have never seen any serious attempt to define a continuum. I do know that math students are seldom successful in arguing that their teacher should assume a continuum of logical correctness when grading.

Irrationality in Neuroscience, Economics, and “AI”

The Irrational Brain Hypothesis is the foundation for a great deal of research. A lot of money has been invested year after year for decades in an effort to make physical systems less irrational. Since a less irrational system is presumably more intelligent, a major objective of research on both biological and artificial intelligence has been to understand how to increase the rationality of a physical system.

The goal of designing a rational physical system is central to the early literature on neural networks. McCulloch and Pitts, Rosenblatt, Minsky, and others sought to understand how neurons, if properly “wired,” could perform conventional logic.  More recently the field has turned towards Bayesian accounts of neurons, in which the logic is that of probabilities. This can be seen in the work of people such as Geoff Hinton, Peter Dayan, and Karl Friston. I further discuss and critique the harmful influence of the Irrational Brain Hypothesis on research in this field on my page titled Bayesian Brain Theory, as well as in older publications (Fiorillo, 2010; Fiorillo, 2012; Fiorillo, 2017) 

Human irrationality is also a foundational assumption of behavioral economics. This field has been recognized with multiple Nobel Prizes in the last two decades for work on human decision-making that is purported to demonstrate “bounded rationality.” This term refers to irrationality of a less irrational sort. It strikes me as more suited to a Nobel Prize than its synonym, “bounded irrationality.”

Nature is Rational

I explain in Nature is Rational that no one can define what it means for a physical system to be irrational. To literally be irrational is inconceivable and impossible. I also argue that what we attribute to irrationality is actually explained by ignorance (lack of information), and the fact that evidence is local in space and time and varies from one observer to another (even within one brain).