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Robert Kurzban

The Evolutionary Psychology Blog

By Robert Kurzban

Robert Kurzban is an Associate Professor at the University of Pennsylvania and author of Why Everyone (Else) Is A Hypocrite. Follow him on Twitter: @rkurzban

Defining Deception

Published 6 November, 2012

At the event that I mentioned in a prior blog post, the workshop entitled, “Lying: The Making of the World” at Arizona State University, the assembled biologists, psychologists, philosophers and others discussed, perhaps less than one might have thought, how to define whatever it was they all assembled to discuss. How should terms the terms “lying” and “deception” be defined?

Defining “lying” seems, to me, harder than defining “deception” because lying needs some sort of account of intentions, which tends to make things, to my taste, unpleasantly untidy. So, I’m only going to talk about deception instead.

Here’s the way that I think about it. Start with this: the reason organisms respond to sensory information they get from the world is because of the lawful relationship between the information that they receive and the actual properties of the thing being perceived. That is, very roughly, things really are what they seem to be, at least enough of the time. To take one example, the reason that certain fish bite at small, wriggling objects is that, over the evolutionary history of the fish in question, things that were small and wriggled were, with some reasonably high probability, things that were beneficial to eat. This relationship is the key element I’ll focus on: the link between the percept and properties of the object. I’ll refer to it as The Link.

The Link need not have been perfect. Perhaps some small, wriggly things fish encountered were inedible, providing no benefits or even were toxic, imposing some cost. Connecting to my prior post about mice, as long as the expected value of eating entities that were “small and wriggly,” according to the information in the fish’s perceptual array was sufficiently high, then selection would favor continuing to eat things that that were “small and wriggly,” even if the actual outcome sometimes was a bad one.

Finding Nemo (delicious)

It goes without saying that if there were some detectable property of the wriggly things that distinguished the good from the bad, evolution could favor more discriminating systems, assuming the cost of the machinery to implement this additional discrimination was lower than the marginal expected value of the additional distinction. That is, if it would be possible but metabolically expensive to add machinery to distinguish small, wriggly prey items from small, wriggly toxic items that did little damage and only rarely were present, selection would have favored the less discriminating, less expensive apparatus.

The Link can be thought of as exploiting, if I may be somewhat Colbertian, truthiness. Because small wriggly things (usually) consist of, as a fact about the world, things that are digestible by the fish, eating them is advantageous for the fish. It’s easy to see that the value of The Link depends on truthiness. If, suddenly, small wriggly things were overwhelmingly harmful to the fish, rather than helpful to the fish, selection would, everything else equal, favor fish who abandoned relying on The Link.

When a given species’ perceptual system exploits a Link, there is potential for other species to manipulate that species’ behavior through systems that produce the stimulus the receiver has been selected to use, taking advantage of the evoked response. So, in the case of the anglerfish, selection can lead to a bit of tissue that produces the stimulus object their prey are designed to use to lure their victims. This bit of the fish’s phenotype breaks the Link, being small and wriggly without having the properties that fish use to feed.

Breaking the Link is how I think deception should be defined. To me, deception occurs when a trait breaks the relationship between stimulus and world that another organism’s phenotype has been designed to exploit. I think this will properly include all the cases that we want to include in the concept, exclude all the ones we want to hold aside, and of course avoid any intentional language. So, in the present case, it seems right that the angler fish’s morphology deceives its prey, violating the usual relationship other fish use to identify prey.

I note in passing that costs and benefits play no role in my proposal here. That is, I don’t insist that cases of deception impose costs on the deceived. Most might well do this, but I leave open the possibility that deception will benefit both deceiver and the deceived. One can imagine cases in which one organism is designed to deceive another organism in such a way that it takes advantage of the Link, but the deceived organism is nonetheless better off or at least no worse off.

So. That’s how I’d define deception. Counterexamples?

  • http://profiles.google.com/hugo.mercier Hugo Mercier

    How do you exclude cases in which the Link is ‘broken’ but for the benefit of the individual? Would that not qualify as ‘broken’?

    • rkurzban

      I’m not sure I understand. Say – and this is just for illustrative purposes – a plant looks like a potential mate to an insect (breaking the Link between looking like a mate and actually being a mate), but in looking like a mate, rewards the “deceived” insect with nectar. This counts as deception on my definition, even though the insect is better off.

      • http://profiles.google.com/hugo.mercier Hugo Mercier

        Sorry for the late reply. What I had in mind where cases of communication through ritualization for instance. They do seem to rely on the Link, but given that they are communicative, calling them deceptive becomes a bit tricky, no?

  • Matthias Flor

    I think your definition in principle is fine.

    A couple of questions: What cases do you mean that we want to hold aside?

    What about mimetic camouflage? E.g. an insect that looks like a leaf or a twig? Would you argue that this breaks the link perceived by an insectivore that “what looks like a leaf is a leaf” and thus not worth eating? I guess the more general question is this: should “active” hiding count as deception? Another example would be fish with luminescent bellies that make perception from below much more difficult. Deception or not?

    • rkurzban

      It seems to me that camouflage is deception, and is captured by the definition, as are the other cases. In the case of bellies, predators are designed to infer that light coming from above is sky; luminescent fish break that link. Should pretending to be the sky be counted as deception? I think it does, but if not, then, yes, my proposal is too broad.

      • Matthias Flor

        I’d rather say that predators are designed to infer that silhouettes (against the sky) are potential prey. No silhouette, no prey, no Link to be broken. To what extent does the absence of a percept constitute a percept?

        Again, do you have any particular cases in mind that you want to exclude but that are somewhat similar to deception?

        • rkurzban

          Well, I don’t count the sky as a lack of a percept; I see it is a percept (along the lines of the light blue percept above me = empty space/sky). I don’t have any particular cases in mind, but am interested in candidate cases.

          • Matt Flor

            Hm, along similar lines: What about prey animals that have been selected for freezing in the presence of a predator because the predator’s vision is optimized for detecting motion. Thus, the prey animal is avoiding detection by exploiting the Link ‘motion –> potential prey’, again exactly by NOT providing a percept used by the predator. That’s not really deception, or is it?

          • http://popsych.org/ Jesse Marczyk

            There’s a difference between the not-sending of a signal (i.e. no motion) versus sending a deceptive signal, so I would say no, not moving is not a type of deception

          • alexandru

            I’d say that freezing to camouflage in instances of predation definitely do fit into Kurzbans’ definition of deception. The “link” between precepts of benefit, and action, is being broken (on the predators side). Therefore deception is at play.

            I think that assuming no action means no signal is erroneous because changing your intended action, is an action within its self.


            Most sensory perception is actually just change through time. Thus no change in time = no perception (at least in humans, although I doubt that it would be very different in animals)

            Also I’m willing to bet that most animals who freeze when in danger tend to have camouflaging adaptations aswel.

            But this would probably vary as a function of how high they are on the predatory list.

            Just my two cents

          • http://popsych.org/ Jesse Marczyk

            Freezing seems comparable to simply not being noticed. The difference arises from, in the case of deception, (1) breaking the link, versus the case of not being noticed, which amounts to (2) the link never being established in the first place.

          • alexandru

            Not being noticed is still deception in my mind, because the prey is simulating an environment that isn’t real.

            If they didn’t know that danger loomed, they would move.

            In other words a link is established between environment and the predator. The prey is breaking this link by feigning reality.

            I don’t see why detection should be a prerequisite for a link.

            For example, a venus fly trap deceives a fly by simulating a link that isn’t existent

            it isn’t a safe flower, it’s a predator.

            The carnivorous flower breaks the link between supposed environment and reality. The fly is deceived… to his dismay

  • http://thomscottphillips.wordpress.com/ Thom Scott-Phillips

    Isn’t the definition too broad? When humans knock down forests, they break The Link for all sorts of organisms that live in the forest. Are the humans being deceptive? Surely not.

    This seems easily fixable though. Deception is breaking a particular type of link, specifically one between *signals* (rather than simply any stimulus) and some state of the world.

    Perhaps this is what you had in mind – but I wasn’t sure, so I thought it worthwhile being explicit.

    • rkurzban

      It doesn’t seem to me that knocking down forests breaks Links of the sort I’m talking about – an organism’s percept and a property of the world. My post was quite short, and so stripped of nuance, but, no, I don’t want to limit the definition to signals. It seems to me so limiting the definition would exclude cases we want to, including the example of the angler fish.

      • Martin H

        Another case demonstrating a too broad conception of deception of yours would I think be all the cases, when one organism (eg. human) exploits the actual domain of a module of another organism by producing a stimulus that meets the input condtions of the proper domain of the module, but wasnt evolved to processes them..eg. moral reasons for the reasoning module (just to illustrate, need not be taken as true)…yet the moral reasons could improve, or may have possitive cognitive effects, on the other organism…why call this a deception….also applicaple to other communicative acts….is this argument valid at all, what you think? I just seem to find many counter examples to your definition…the term deception implicitly caries a negative tone with it…like benefiting one, harming other or so..it can ofetn be benefitial to both, regardles if it is an sitmulus belonging to the actual domain and not to the proper domain…thanks

      • Thom Scott-Phillips

        Before the forest was knocked down, there was a correlation between, say, things being green (the percept), and things been edible for some species in the forest (a property of the world). So whenever the species (lets say they’re insects of some sort) fed on these green things, they exploited this correlation i.e. The Link.

        Then the humans knocked the forest down, and put in its place concrete houses, which they painted green. So The Link has been broken, and the insects that previously exploited it can no longer do so. Surely we wouldn’t want to say that the humans have deceived the insects?

        I suspect I am missing something, but I don’t presently see what.

        • rkurzban

          Oh, I think I misunderstood your comment. You’re not saying that the knocking down of the forest meets my definition, but rather the houses that, being green, deceive the insects who feed on green things. Yes, in such a case, if the properties of the (inedible to insects) artifacts meet the input conditions of the insects’ food-discovery systems, then that would count as deception under my definition. It seems to me that there is an interesting (natural language) sense in which, yes, the insects have been deceived, though there is no intention on the part of the human agents. But, sure, if you think that this makes the definition too inclusive, then it would need to be narrowed. I actually want to include such cases. (As an aside, my sense was that most insects aren’t trichromatic, as we are and, in fact, entities likely to try to feed on our houses, termites, aren’t deceived at all…)

          • Thom Scott-Phillips

            Ah, no, we’re misunderstand each other, and it’s my fault. My main point is indeed that knocking down the forest in the first place does satisfy your definition: it breaks the link.

            I added the comment about the green houses only to reiterate that, but I fear it may have been counterproductive. Suppose instead that the concrete houses are all colours but green. There is no more green in this new environment. The link is broken – but I don’t see how we can say that the humans have deceived the insects.

            (I imagine you’re right that the insects aren’t trichromatic, so I could have constructed a better thought experiment. But it doesn’t change the substance of the point.)

  • Eric Schniter

    I’d like to chime in on Thom’s comment, guessing that I understood his angle. Borrowing from signal theory in biology, my coauthors and I distinguish distinguish cues from signals from coercion (see similar definitions by Diggle et al., 2007; Scott-Phillips, 2008) as follows.

    Cue. Any behavior or feature that (i) affects the behavior of other organisms; (ii) which is effective because the effect has evolved to be affected by the behavior or feature; but which (iii) did not evolve.

    Signal. Any behavior or feature that (i) affects the behavior of other organisms; (ii) evolved because of those effects; and (iii) which is effective because the effect (the response) has evolved to be affected by the behavior or feature.

    Coercion. Any behavior or feature that (i) affects the behavior of other organisms; (ii) evolved because of those effects; but which (iii) is effective for some reason other than that the effect has evolved to be affected by the behavior or feature.

    I mention this because deception, as we often think of in the case of language and intentionally counter factual statements, is typically an issue of signals. Camouflage is coercion. The argument is that signals and coercion have come about via different evolutionary routes.

    • rkurzban

      Eric, I’ve written about the signal/cue distinction elsewhere (http://bit.ly/Z8NGNt), and, if I understand your definition of coercion, then it seems to me that on my definition, all cases of deception are coercion (on your definition), but not the reverse. That is, deception is one sort of coercion. Having said that, your definition casts a broad net, does it not? A caterpillar munching a leaf is “coercing” it, if I understand correctly. That’s fine with me, but seems to stretch the natural language sense of the word a bit (which, again, is fine). But I resist your claim that about deception and signals. Indeed, the example in my post is a case in which (on the definition I endorse), the wiggling of worms is a cue, not a signal, and the angler fish takes advantage of the way that fish use the cue. But, broadly, as you can tell, I like the direction of these definitions, which place the issue in terms of function, which I believe is the most clarifying route to defining such terms. Anyway, thanks for the comment.

  • http://www.facebook.com/gojaejin Jeremy J. Goard

    One complication that occurs to me, for behaviors that are sufficiently complex, is the question of whether and how a baseline can be determined. For example, I think it would be uncontroversial that a woman wearing makeup or a man of moderate means wearing an expensive tailored suit are examples of deception in your sense. But deception relative to what? If a woman doesn’t put on any makeup, but does take a shower and brush her hair (instead of going to work with tangled hair and a natural body odor), is that still going to count as deception?

    There’s an empirical question here, namely how we can determine what information different such indices give to the average perceiver. But there’s also a philosophical question: is there any basis on which it makes sense to pick out any one point as a “true” or “honest” signal?

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