Our evolutionary history has shaped our inference systems as evolved responses to recurrent problems in ancestral conditions.So we must
These stringent requirements explain why evolutionary psychology is still very much in its infancy. We cannot just consider a human capacity (e.g., the capacity to read and write) and make up a story that would make it adaptive (written communication is very convenient). In this case, it happens that literacy does not require a specific system in the brain. It just recruits systems that served throughout our history [and still serve other purposes (recognition of visual shapes, segmentation of words into syllables, motor control of the hand and wrist, etc.). In some domains, it is quite clear that the way our inference systems work is an outcome of evolution, because our choices have direct consequences on our survival and reproductive success. For example, evolutionary psychologists Don Symons and David Buss have put together a precise account of many aspects of human sexual behavior: how people choose partners, what they find attractive, as well as how they gauge the reliability of these partners for long-term cooperation and child rearing.
Life in ancestral environments was fraught with danger, not just from the obvious predators but also frem a variety of microbes, viruses and toxins. Ancestral foods obtained through foraging, scavenging and hunting were quite "natural" and therefore far from healthy. Many plants are full of dangerous toxins and so are dead animals. Also, many animals carry pathogens that adapt easily to life in a human body. The danger is especially high for a "generalist" species like humansthat is, one that finds its nutrients in a great variety of sources and adapts to new environments by changing its diet. Being a generalist species requires not only that you have immune defenses like most other species but also that you make specific cognitive adaptations to minimize the danger of contamination and contagion. Rats, too, are generalists; this shows in their extremely cautious approach to novel foods, and in the way they quickly detect the correlation between a new food and various somatic disorders. They detect such connections better than other, non-food-related correlations, which shows that the system that produces such inferences is indeed specialized.
Humans too have special cognitive adaptations in this domain. For instance, very young children are open to a whole variety of tastes as long as the food is given by their caregivers, which helps them adapt to local conditions; later, they become rather conservative, which limits their forays into dangerous foods. Pregnant women develop specific food aversions, mainly to tastes of toxin-rich foods. Morning sickness seems to target precisely those foods that would be dangerous to fetal growth in an ancestral environment. Food is obviously not the only source of danger of this kind. Contact with rotting corpses or with wounded or diseased people, ingestion of feces or dirt: these are avoided for good evolutionary reasons.
Indeed, the human mind seems to include a specific inference system that deals with such situations and triggers strong emotional reactions to even to the mere suggestion of such situations. Psychologist Paul Rozin, who has studied the psychology of disgust, its connections to evolved food preferences and its relation to the risk of contamination, showed that this contagion system obeys specific inferential principles. First, it assumes that the source of danger is not necessarily visible; what makes a rotting carcass a bad source of food was not detectable before microscopes and microbiology. Second, the contagion system assumes that even limited contact, however brief, with a source of danger transmits the whole of the risk. In other words, there is no "dose-effect" here. Contagious substances do not lose their harmful powers with dilution. Third, the system specifies that any contact with sources of pollution transmits it, although the aversive reactions are especially strong with ingestion. These principles are specific to the domain considered. The contagion inference system may in some circumstances seem overly cautious, as when subjects in Paul Rozin's experiments refused to drink from a glass that once sheltered a cockroach and that was then thoroughly disinfected. But the system was tuned to ancestral conditions, under which there was no such thing as thorough disinfecting.
LIFE IN THE COGNITIVE NICHE
Taking this evolutionary stance leads us to ask very general questions, such as: What do humans need? What is special about their needs, as opposed to those of giraffes and wombats? Obviously, humans need oxygen to breathe and a complicated cocktail of nutrients to sustain themselves, but that is fairly general among animals. What humans especially need, more than any other species, are two types of goods without which existence is impossible. They need information about the world around them; and they need cooperation with other members of the species. These two are so much a part of our environment that it is diffficult to realize to what extent they are, literally, a matter of daily survival; it is also diffficult to realize to what extent our minds have been shaped through millennia of evolution to acquire these commodities and have become ever more dependent upon their supply.
Humans are information-hungry
Human behavior is based on a rich and flexible database that provides parameters for action. Very little of human behavior can be explained or even described without taking into account the massive acquisition of information about surrounding situations. This is why some anthropologists have described the proper environment of humans as a "cognitive niche". Just as frogs need ponds and whales need seawater, humans are constantly immersed in a milieu that is indispensable to their operation and survival, and that milieu is information-aboutthe-environment. The journalistic cliche that this is the "information age" is misleading if it suggests that in the past, either recent or distant, we did not depend on information.
Humans are cooperators
Humans have for a long time- long enough to make a difference in evolutionary terms - lived in organized groups and in intense social interaction. Humans need cooperation because they depend on rich information, well beyond what individual experience can provide. Other people provide most of this information. Also, most of what humans do requires cooperation. What I said above about foraging and hunting makes sense in the context of some people carrying out part of an operation and others being able to do their part because of the first group's actions. This is cooperation not just in the simple sense of "doing things jointly" but rather as "doing different things in a coordinated manner." Now cooperation requires specific capacities and dispositions.
These general requirements of human existence have two important consequences: Because they only survive through cooperation and because they need information, humans are generally dependent upon information provided byother humans. This is not to deny that humans can acquire vast amounts of information by direct experience.
But the fact is, even that could not be acquired without massive transfers of information from other conspecifics, to a degree that is unequaled in any other species. Humans depend upon information and upon cooperation, and because of that they depend on information about other people's mental states - that is, what information they have and what their intentions are. No joint hunting expedition, war raid or marriage negotiation can be organized without precise monitoring of what other people want and believe.
Once you are told that whales live in seawater you may not be surprised to find out that their capacities and dispositions were tailored by natural selection to provide a reasonable fit to these conditions. The same is true of human capacities and dispositions, once you understand that the proper milieu of human existence is tbat of other people's information. This means that we must explore yet another batch of inference systems in the mental basement.
Inference systems in the social mind
That humans live in the cognitive niche, and that most elements of that informational milieu are provided by other humans, results in specific behaviors and capacities. Most of these are very familiar - so familiar indeed that it is sometimes difficult to realize that they require specific cognitive equipment. A few of these behaviors and capacities are discussed below.
A hypertrophied social intelligence. What we call social intelligence in many species are special capacities for social interaction. We have hugely complex social interaction, compared to other species, partly because we have hugely complex systems that represent what others are up to and why. For instance, here are two aspects of social intelligence that are hugely developed in humans:
(1) figuring out complex embedded states - for instance understanding that "Mary knew that Peter resented the fact that she had agreed with Paul when he said Jenny was too clever for Mark";
As I said above, what we call "intuitive psychology" or "theory of mind" is a federation of brain structures and functions, each of which is specialized in particular tasks:
A taste for gossip. Although we tend to despise it or downplay its importance, gossip is perhaps among the most fundamental human activities, as important to survival and reproduction as most other cognitive capacities and emotional dispositions. Gossip is practiced everywhere, enjoyed everywhere, despised everywhere. Why is that? We can better understand these three features if we recall what gossip is about. Its main focus is information about other people, preferably information that they would rather not have broadcast, and centers on topics of adaptive value such as people's status, resources and sex. Gossip loses much of its interest when it strays from these topics, as demonstrated by our common attitude toward people who feverishly acquire and exchange information in other domains. Think of those obsessive fans who exchange information about every track of every record ever issued by their favorite band, when and where the cover photographs were taken, etc. Or consider the more extreme case of British "trainspotters." (For non-British readers, I should explain that these are people who spend entire weekends watching trains; their goal is to tick as many boxes as possible in a catalogue of all the rolling stock used by every railway company, including every locomotive and carriage type.) Such characters tattle about matters of no relevance to social interaction. We do not praise them for that; we just think they are not quite normal.
There is no human society without gossip. Yet there is virtually no human group where gossip is praised for its great informative value, for its contribution to social interaction, for its great usefulness. Why is that? The universal contempt for gossip stems from two equally important factors. One is that as much as we want to hear about other people's status and sex and resources, we are reluctant to broadcast such information about ourselves. Again, this just shows that information is a resource: it is not to be squandered.
Adaptations for social exchange. Nothing is easier to understand than situations of social exchange. That you will gain a certain benefit (get a share of the meal) if you accept to pay a certain cost (bring a bottle) is so natural that the subtle reasoning behind such situations seems self-evident. The inferences are indeed automatic (if the meal is lavish and your bottle less than respectable, people will not be that grateful) but that is because the inference system is quite efficient. Social exchange is certainly among the oldest of human behaviors, as humans have depended on sharing and exchanging resources for a very long time. Evolutionary psychologists Leda Cosmides and John Tooby pointed out that people become much better at solving complex logical tasks if these are presented as social exchange problems; it does not matter if the situation is exotic. To check whether an imaginary tribe actually abides by the rule "If people get their faces scarified then they have a right to eat buffalo," subjects spontaneously check for buffalo eaters with intact faces (rather than scarified individuals who do not eat buffalo). Inferences in such situations follow a specific "check for cheaters" rule rather than a general logic. Indeed, subjects are confused when asked to check an equivalent rule that does not pertain to social exchange, such as "If people get their faces scarified then they have visited Peking." Psychologists observed these same experimental results in American college students and Shiwiar hunter-gatherers in the Amazon.
Evaluation of trust. That humans depend on cooperation creates strategic problems, where the value (the expected benefit) of a particular move depends on whether someone else makes a particular move (not necessarily the same one). Ideally, one could choose to cooperate only with people who are forced to cooperate. Whenever you pay for something you can of course draw a gun and threaten the shopkeeper to be sure that you get the correct change. This is not really possible in most circumstances, but we have capacities that compensate for that. One is that we can decide to cooperate with people on the basis of particular signals from which (we think) we can infer that they are cooperators.
Now this part of the computation is crucial, but we are not really aware of it. This situation is in fact general. Sociologists Diego Gambetta and Paul Bacharach have studied extensively the signals by which people evaluate other people's trustworthiness in everyday situations. They show that in many contexts (e.g., Would you let the person who arrived just behind you into the building, even though she has not dialed the appropriate code or rung the bell?) people are able to evaluate whether certain signals are reliable or not. This requires that they compute both the significance of the signal and the probability that it is faked. All this is done automatically and quickly: not because the inferences are simple but because we have specialized systems that carry out this computational work.
Coalitional dynamics. This is another common feature of human interaction. People will spontaneously form groups where a certain degree of trust ensures cooperation and mutual benefits. Biologist Matt Ridley coined the term "groupishness" to describe the human tendency to join groups. Modern ethnic conflicts, but also the harmless social dynamics of fashions or the minor coalitions within any large classroom, office, congregation, etc., illustrate the power of this propensity.
Note that coalitions are a very special form of association. To have a common goal is not sufficient to build a coalition; you and I may wish our streets were cleaner, but that does not bring us into a coalition. It is not even sufficient that people are aware of having the same goal and cooperate to achieve that goal. For instance, factory workers need to coordinate their work to produce a manufactured good but they do not construe this as a coalition. The latter presupposes an activity in which joining is (presumably) voluntary, defection is possible, benefits accrue with cooperation and there is a notable cost in being a cooperator when others defect.
Group action will allow you to reap great benefits as long as everyone is in it together. But then in many situations it may be much more profitable for some individuals to withdraw cooperation at an awkward moment. Your hunting partner might put you in great danger by running for his life precisely when he was supposed to attack. Your comrade in the office conspiracy might spill the beans to please the boss. There is just no ironclad guarantee that people will not blab or run away, or to put it more generally, defect to protect or enhance their immediate interest. This is why so few species actually have coalitions (chimpanzees and dolphins build alliances but not to the same scale and with the same stability as the human version). Coalitions require complicated computation, and therefore the mental capacities to run these computations in an intuitive, automatic way.
To make this clear, it may be of help to list the conditions that must obtain in a coalition:
I describe these conditions in some detail - however painfully obvious they may all seembecause this shows how building coalitions requires complex computation. The fact that coalitions seem such a simple and obvious thing to us does not prove that their functioning is simple but rather that we have the kinds of minds that compute all this without much difficulty, which is different. Nobody in any human culture needs much instruction to figure out how cooperation is established between partners or how to detect potential threats to cooperation. Also, note how coalitional behavior is so easily developed by young children, in the absence of much explicit instruction (and indeed very often against dismayed parents'recommendations).
Incidentally, this discussion in terms of cost and benefit, cooperation and defection, may seem very abstract. We tend to think that we just have "feelings" about such situations. This is true in a sense: Feelings are the most salient reactions we are aware of. But feelings are the outcome of complex calculations that specialized systems in our minds carry out in precise terms. For instance, some of my recently arrived African friends were baffled that people in Europe could get so worked up by parking-space "theft." They could understand it, in some abstract way, but they just did not "feel" the anger. After a few weeks of driving their own cars in the city they displayed the same emotional reactions as the locals. It is not that their abstract "conceptions" of what matters and what does not had changed. But they had acquired the information that a parking space is a very scarce resource, and their emotional systems had adjusted to that information.
DECOUPLING AND CONSTRAINTS
A human mind is not condemned to consider and represent only what is currently going on in its immediate environment. Indeed, human minds are remarkable in the amount of time they spend thinking about what is not here and now.
Decoupled cognition is crucial to human cognition because we depend so much on information communicated by others and on cooperation with others. To evaluate information provided by others you must build some mental simulation of what they describe. Also, we could not carry out complex hunting expeditions, tool making, food gathering or social exchange without complex planning. The latter requires an evaluation of several different scenarios, each of which is based on nonactual premises (What if we go down to the valley to gather fruit? What if there is none down there? What if other members of the group decide to go elsewhere? What if my neighbor steals my tools? and so on). Thinking about the past too requires decoupling
As psychologist Endel Tulving points out, episodic memory is a form of mental "time travel" allowing us to reexperience the effects of a particular scene on us. This is used in particular to assess other people's behavior, to reevaluate their character, to provide a new description of our own behavior and its consequences, and for similar purposes.
Decoupled cognition appears very early in children's development when they start to "pretend-play," using a variety of objects as though they were other objects (e.g., a bar of soap as a car, a puppet as a person, etc.). Now doing this requires a subtle mechanism that tells you which aspects of the real environment should be bracketed off, as it were, and which still count as true in the imagined scenario. Psychologist Alan Leslie demonstrated spectacular examples of this capacity. Children pretend-pour pretend-tea out of an empty teapot into several cups. (They are carefnl to align the spout of their teapot with the cup, because in the pretend-scenario liquids fall downward as they do in the real world. This aspect of the scenario is handled by intuitive physics as if there were real liquid in the pot.) Then an experimenter knocks over one of the cups, laments the fact that the pretend-tea is spilled all over the table, and asks the child to refill the empty cup. Now three-year-olds faced with this situation, that is, with two (actually) empty cups only one of which is also (pretend-)empty, do not make mistakes and pretend-fill only the pretend-empty one, not the actually empty one that is still pretend-full. This kind of virtuoso performance is in fact involved in all situations of pretense. The child's cognitive system can handle the nonactual assumptions of the situation and run inferences of the intuitive ontology that make sense in that imagined context but not in the real context.
Decoupling is also necessary to produce external representations, another universal capacity in humans. Toys, statues, rock paintings and finger drawings in the sand are not the same as what they represent. To make sense of them, our inference systems must block certain inferences - the path through the forest is one inch wide on the drawing but it is not that narrow in actual factand maintain others - that the path in the sand turns left means that the actual one turns leit too. So the interpretation of external representations can be subtle. Indeed, in many cases we intnitively consider that what external representations stand for depends much more on their creators' intentions than on what they look like. Psychologist Paul Bloom showed that very young children share this subtle assumption. For them two strictly identical drawings are in actual fact representations of different objects (e.g., a lollipop and a balloon) if that is what the creators intended.
It is certainly useful to reason away from the here and now; but that works only if such reasoning is tightly constrained. If our inferences ran wild - for example, "If we go down to the valley, my dog will lose its teeth" or "If my brother is sad, this telephone will break into pieces"they would not provide the basis for effficient behavior. Note that these strange inferences are not strange just because their consequences seem outlandish. You could instead say "If I feed the dog nothing but candy-canes it will lose its teeth" or "If you put the telephone in the tumbler-drier it will break into pieces." So it is the connection between the hypothesis and the consequence that is or is not sensible.
The crucial point to remember about decoupled thoughts is that they run the inference systems in the same way as if the situation were actual. This is why we can produce coherent and useful inferences on the basis of imagined premises. For instance, the sentence "If kangaroos had shorter legs, they would jump higher" seems implausible, and "If kangaroos had shorter legs, they would eat broccoli" seems to make no sense at all. The first inference sounds plausible because it is supported by our inference systems. Our intuitive physics assumes that a stronger push will result in a longer trajectory, therefore that longer legs should produce longer jumps. In the same way, if I tell you that I saw a tiger in the forest yesterday, you will probably infer that I was in the forest yesterday, because your intuitive psychology requires that condition.
Hypothetical scenarios suspend one aspect of actual situations but then run all inference systems in the same way as usual. If this sounds familiar, it is because I already mentioned it in my presentation of supernatural concepts, which include one violation of expectations ("If some agents were invisible... ") and then run all relevant inferences in the same way as usual ("...we could not see them, but they would see what was going on"). Supernatural concepts are just one consequence of the human capacity for decoupling representations.