# Why Motivated Reasoning?

There’s a standard story which says roughly "motivated reasoning in humans exists because it is/was adaptive for negotiating with other humans". I do not think that story stands up well under examination; when I think of standard day-to-day examples of motivated reasoning, that pattern sounds like a plausible generator for some-but-a-lot-less-than-all of them.

### Examples

Suppose it's 10 pm and I've been playing Civ all evening. I know that I should get ready for bed now-ish. But... y'know, this turn isn't a very natural stopping point. And it's not that bad if I go to bed half an hour late, right? Etc. Obvious motivated reasoning. But man, that motivated reasoning sure does not seem very socially-oriented? Like, sure, you could make up a story about how I'm justifying myself to an imaginary audience or something, but it does not feel like one would have predicted the Civ example in advance from the model "motivated reasoning in humans exists because it is/was adaptive for negotiating with other humans".

Another class of examples: very often in social situations, [the move which will actually get one the most points is to admit fault and apologize](https://www.lesswrong.com/posts/xiTLBuhEMmoyeor6D/apologizing-is-a-core-rationalist-skill). And yet, instead of that, people instinctively spin a story about how they didn't really do anything wrong. People instinctively spin that story even when it's pretty damn obvious (if one actually stops to consider it) that apologizing would result in a better outcome for the person in question. Again, you could maybe make up some story about evolving suboptimal heuristics, but this just isn't the behavior one would predict in advance from the model "motivated reasoning in humans exists because it is/was adaptive for negotiating with other humans".

That said, let’s also include an example where "motivated reasoning in humans exists because it is/was adaptive for negotiating with other humans" *does* seem like a plausible generator. Suppose I told a partner I’d pick them up on my way home at 6:00 pm, but when 6:00 pm rolls around I’m deep in an interesting conversation and don’t want to stop. The conversation continues for a couple hours. My partner is unhappy about this. But if I can motivatedly-reason my way to believing that my choice was justified (or at least not *that* bad), then I will probably have a lot easier time convincing my partner that the choice was justified - or at least that we have a reasonable disagreement about what’s justified, as opposed to me just being a dick. Now personally I prefer my relationships be, uh, less antagonistic than that whole example implies, but you can see where that sort of thing might be predicted in advance by the model "motivated reasoning in humans exists because it is/was adaptive for negotiating with other humans".

Looking at all these examples (and many others) together, the main pattern which jumps out to me is: motivated reasoning isn't mainly about fooling others, it's about fooling oneself. Or at least a part of oneself. Indeed, there's plenty of standard wisdom along those lines: "the easiest person to fool is yourself", etc. Yes, there are *some* examples where fooling oneself is instrumentally useful for negotiating with others. But humans sure seem to motivatedly-reason and fool themselves in lots of situations which don’t involve any other humans (like the Civ example), and situations in which the self-deception is net harmful socially (like the apology class of examples). The picture as a whole does not look like "motivated reasoning in humans exists because it is/was adaptive for negotiating with other humans".

So why do humans motivatedly reason, then?
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I’m about to give an alternative model. First, though, I should flag that the above critique still stands even if the alternative model is wrong. "Motivated reasoning in humans exists because it is/was adaptive for negotiating with other humans" is still basically wrong, even if the alternative I’m about to sketch is also wrong.

With that in mind, model part 1: motivated reasoning simply isn’t adaptive. Even in the ancestral environment, motivated reasoning decreased fitness. The obvious answer is just correct.

### What? But then why didn’t motivated reasoning evolve away?

Humans are not nearly fitness-optimal, especially when it comes to cognition. We have multiple arguments and lines of evidence for this fact.

First, just on priors: humans are approximately the stupidest thing which can cognitively “take off”, otherwise we would have taken off *sooner* in ancestral history, when we were less smart. So we shouldn’t expect humans to be optimal minds with all the bugs worked out.

Second, it sure does seem like humans have been evolving at a relatively quick clip, especially the brain. It’s not like we’ve been basically the same for tens of millions of years; our evolution is not at equilibrium, and wasn’t at equilibrium even before agriculture.

Third, it sure does seem like humans today have an awful lot of cognitive variation which is probably not fitness-neutral (even in the ancestral environment). The difference between e.g. an IQ-70 human and an IQ-130 human is extremely stark, mostly genetic, and does not seem to involve *comparably large* tradeoffs on other axes of fitness in the ancestral environment (e.g. IQ-130 humans do not get sick twice as often or burn twice as many calories as IQ-70 humans).

So in general, arguments of the form “<apparently-suboptimal quirk of human reasoning> must be adaptive because it didn’t evolve away” just… aren’t that strong. It’s not zero evidence, but it’s relevant mainly when the quirk is something which goes back a lot further in the ancestral tree than humans.

(This does mean that e.g. lots of other mammals engaging in motivated reasoning, in a qualitatively similar way to humans, would be much more compelling evidence that motivated reasoning is adaptive.)

### Ok, but then why *do* humans motivatedly reason?

Even if we accept that human cognition is not nearly fitness-optimal, especially when it comes to cognition, that doesn’t tell us which particular cognitive bugs humans have. It doesn’t predict motivated reasoning *specifically*, out of the bajillions of possibilities in the exponentially large space of possible cognitive bugs. It doesn’t *positively* predict motivated reasoning, it just *negates* the argument that motivated reasoning must somehow be fitness-optimal.

Our above argument does predict that motivated reasoning must have shown up recently in human evolutionary history (otherwise it *would* have evolved away). And motivated reasoning does seem innate to humans by default (as opposed to e.g. being installed by specific cultural memes), so it must have come from one or a few genetic changes. And those changes must have increased fitness overall, otherwise they wouldn’t have spread to the whole population. So, insofar as we buy those premises… motivated reasoning must be a side-effect of some other evolutionarily-recent cognitive changes which were overall beneficial, despite motivated reasoning itself being net negative.

Can we guess at what those changes might be?

Observation: in examples of motivated reasoning, it feels like our brains have two internal plan-evaluators. One of them is a relatively short-sighted, emotionally-driven plan evaluator. The other is focused more on the long term, on reputation and other people’s reactions, on all the things one has been told are good or bad, etc; that one is less myopic. The basic dynamic in motivated reasoning seems to be the shorter-range plan-evaluator trying to trick the longer-range plan evaluator. 

Thus, model part 2: the longer-range plan evaluator is a recent cognitive innovation of the human lineage. Other animals sometimes do long-range-oriented things, but usually not in a [general purpose](https://www.lesswrong.com/posts/6mysMAqvo9giHC4iX/what-s-general-purpose-search-and-why-might-we-expect-to-see) way; general purpose long-range planning seems pretty human specific. The shorter sighted plan evaluator is still just doing basically the same thing it’s always done: it tries to find outputs it can feed to the rest of the brain which will result in good-feeling stuff short term. In humans, that means the short sighted search process looks for outputs it can feed to the long range planner which will result in good-feeling stuff short term. Thus, motivated reasoning: the short sighted search process is optimizing against the long range planner, just as an accident of working the same way the short sighted process always worked throughout evolutionary history.

For example, when I’m playing Civ at 10 pm, my long range planner is like “ok bed time now”, but my short range planner is like “oh no that will lose good-feeling stuff right now, let’s try spitting some other outputs into rest-of-brain to see if we can keep the good-feeling stuff”. And sometimes it hits on thoughts like “y'know, this turn isn't a very natural stopping point” or “it's not that bad if I go to bed half an hour late, right?”, which mollify the long range planner enough to keep playing Civ. In an ideal mind, the short range and long range planners wouldn’t optimize against each other like this; both do necessary work sometimes. But humans aren’t ideal minds, the long range planner is brand spanking new (evolutionarily) and all the bugs haven’t been worked out yet. The two planners just kinda both got stuck in one head and haven’t had time to evolve good genetically hardcoded cooperative protocols yet.