First of all, that is one handsome bonobo. You could easily put him in a movie where he has to plan Cameron Diaz’s wedding to a mean investment banker and she falls in love with him, only to have her arms twisted out of the sockets when they can’t agree on who gets to eat an orange peel. Anywhom, we’re thinking about chimps/Cameron Diaz because of this New York Times article, in which various scientists claim that human beings developed reasoning to win arguments rather than to discern the truth. Those of you who have exhausted your meager allotment of Times stories can read one of the original scholarly articles. I quote from the abstract:
Our hypothesis is that the function of reasoning is argumentative. It is to devise and evaluate arguments intended to persuade. Reasoning so conceived is adaptive given the exceptional dependence of humans on communication and their vulnerability to misinformation.
The gist of this theory is that human beings didn’t develop the brain mechanisms that facilitate reasoning in order to figure out the best way to get a coconut out of a high tree; we developed reasoning to convince some other idiot to go up there and get it for us. That explains the persistence of various reasoning fallacies, including the notorious confirmation bias. It also explains why, from a purely adaptive standpoint, many of the most successful public reasoners speak in a jumble of appeals to patriotism, non-thetic assertions and ad hominem arguments.* Socrates, by comparison, was nominated to drink poison via democratic assembly. So clearly there’s some evidence here.
Yet the argumentative theory of reason entails two serious contradictions. The first is fairly obvious: if the purpose of reasoning is to win arguments, how do we decide which position to win from? Even if I take an entirely instrumental view of truth, believing that the whole apparatus of knowledge and deduction is for exercising power over people, I still have to decide for myself how I want that power to be used. In many ways, this is a weird version of the free will problem: I can do what I want, but how do I choose what I want? It would seem, on the surface at least, that my decisions about which positions to dishonestly advocate to others require some first honest reasoning with myself.
But this objection can be answered on the terms of the original hypothesis: I decide which position to advocate arbitrarily, either by obedience to my own unreasonable impulses or under the influence of some other argumentative reasoner. Yet still we run into a problem. If I reason only to win arguments, what is the mechanism that allows me to be convinced?
Here is the second contradiction, implicit in the phrase “logical fallacy.” If a deductively bad argument works on me, it is because I have some notion of Truth that the argument appears to satisfy. It’s not like I accept the argument even as I recognize it as false, out of deference to the other person’s superior convincing-people ability. Consider that classic mistake of reasoning, affirming the consequent. Socialists want to implement a single-payer health care system; therefore, all people who support a single-payer system must be socialists. If this claim works on me despite its logical fallacy, it is because I have mistaken it for truth. As an auditor, I will not accept reasoning whose sole value is that it appears convincing, even though I identify it as otherwise.
So the argumentative theory of reasoning appears airtight from the perspective of convincing others, but significantly less so from the standpoint of personally evaluating a proposition. And if our hypothesis is that the evolutionary purpose of reasoning is to win arguments, but only in the context of arguing with people, I do not anticipate an enthusiastic peer review. It seems we are making a more modest argument: that reasoning fallacies have persisted because they are useful for winning arguments, even when we know better than to use them ourselves. When it comes to what we consider valid reasoning, we keep two sets of books.
If you find that hypothesis depressing, consider the corollary: we are generally more interested in convincing others of our position than in identifying the truth. There is another way to put this, outside the language of evolutionary biology: people are really confident. Everyone walks around right about everything, which is why we had to agree on rules of logical reasoning in the first place. Some people simply will not join your team until you beat them at the game.