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The Paranoid Optimist: An Integrative Evolutionary Model of Cognitive Biases

Authors:

Abstract

Human cognition is often biased, from judgments of the time of impact of approaching objects all the way through to estimations of social outcomes in the future. We propose these effects and a host of others may all be understood from an evolutionary psychological perspective. In this article, we elaborate error management theory (EMT; Haselton & Buss, 2000). EMT predicts that if judgments are made under uncertainty, and the costs of false positive and false negative errors have been asymmetric over evolutionary history, selection should have favored a bias toward making the least costly error. This perspective integrates a diverse array of effects under a single explanatory umbrella, and it yields new content-specific predictions.
The Paranoid Optimist -- 1
An Integrative Evolutionary Model of Cognitive Biases
University of California, Los Angeles,
Communication Studies and Department of Psychology
&
tle
Psychology, Brain and Behaviour,
ome Building,
University of Newcastle,
Framlington Place
Newcastle,
NE2 4HH, UK
Author Note: We are grateful to Clark Barrett, Daniel Fessler, Garth Fletcher, Joachim Krueger,
Mark Schaller and one anonymous reviewer for helpful comments on an earlier draft of this
article, and to Karthik Panchanathan and Randolph Nesse for providing useful background for
the mathematical modeling. We thank David Buss for bringing the auditory looming effect to
our attention and for insights on the fundamental attribution error and disease avoidance
phenomena.
The Paranoid Optimist:
Martie G. Haselton
Daniel Net
Henry Wellc
April 8, 2005
The Paranoid Optimist -- 2
Abstract
Human cognition is often biased, from judgments of the time of impact of approaching objects
ese effects and
rspective. In this
ment
alse positive and
false negative errors have been asymmetric over evolutionary history, selection should have
favored a bias toward making the least costly error. This perspective integrates a diverse array of
effects under a single explanatory umbrella and it yields new content-specific predictions.
all the way through to estimations of social outcomes in the future. We propose th
a host of others may all be understood from an evolutionary psychological pe
paper we elaborate error management theory (Haselton & Buss, 2000). Error manage
theory predicts that if judgments are made under uncertainty, and the costs of f
The Paranoid Optimist -- 3
The Paranoid Optimist:
An Integrative Evolutionary Model of Cognitive Biases
Better safe than sorry.
Noth
e second
et both seem to
capture aspects of human psychology. A person following both maxims would be a paranoid
optimist, taking chances in some domains while simultaneously being very fearful of certain
r management theory,
evolve.
tic is
ons in that
domain throughout our evolutionary history. This perspective suggests that one of the curiosities
of human cognition—the fact that it seems riddled with biases—may be a functional feature of
mechanisms for making judgments and decisions.
ate the time-
nection
n, Mineka &
own, 1988),
which cause them to overestimate the likelihood that they will succeed in spite of the adversity
they face. Evidence in these domains and many others suggest that humans possess a multitude
of biases, or propensities to adopt one belief on the basis of more slender evidence than would be
required to believe in an alternative.
(Folk Wisdom)
ing ventured, nothing gained. (Contradictory Folk Wisdom)
These two wisdoms seem contradictory. The first urges caution, whereas th
reminds us that we have nothing to lose and should throw caution to the wind. Y
kinds of harm. We will argue, using insights from signal detection and erro
that there are good evolutionary reasons why the paranoid optimist mind could
Furthermore, in which domains it is best to be paranoid and in which to be optimis
predictable from the pattern of recurrent costs and benefits associated with decisi
Human cognition has often been shown to be biased. Perceivers underestim
to-impact of approaching sounds (Neuhoff, 1998, 2001), and overestimate the con
between pictures of snakes and unpleasant outcomes like electric shocks (Tomarke
Cook, 1989). People also appear to have a variety of positive illusions (Taylor & Br
The Paranoid Optimist -- 4
Until recently, many psychologists have been content to describe these phenomena, their
contexts of appearance, and possible implications, without much concern for their ultimate
ends to be
imple heuristic
hers (e.g., Miller
erve the
proximate function of preserving self-esteem or subjective happiness for the ego-centered human
animal (Crocker & Park, 2004; Greenberg, Pyszczynski, Solomon & Pinel, 1993; Kunda, 1990).
Researchers offer evoked biases as examples of just such imperfections.
n and Buss
xual intent
ction is limited
primarily by the number of sexual partners to whom they gain sexual access, a bias that caused
men to err on the side of assuming sexual interest would have resulted in fewer missed sexual
opportunities, and hence greater offspring number, than unbiased sexual inferences. Therefore,
ample further
second example occurs in the perceptual domain. Neuhoff (2001) argued that the
perc ner than they
coming object,
than too late.
Here we extend the insight that biased systems can result in higher fitness relative to
unbiased ones, and demonstrate that a wide variety of biases, both positive (optimistic) and
negative (paranoid), may be brought under a single explanatory umbrella. We elaborate error
origin. As Krebs and Denton (1997) note, in as much as explanation is needed, it t
proximate in nature. Psychologists argue that cognition is performed by a set of s
procedures, which are effective in many circumstances but prone to error in ot
& Ross, 1975; Kahneman et al., 1982). Or, in social domains, biases in judgment s
A noteworthy exception exists in the domain of sexual inference. Haselto
(2000) argued that the documented tendency for men to overestimate women’s se
could be an adaptive bias designed by natural selection. Because men’s reprodu
natural selection should favor sexual overperception in men. (We discuss this ex
below.) A
eptual bias towards thinking that incoming sources of sound will arrive soo
actually do may be adaptive, because it is better to be ready too early for an in
The Paranoid Optimist -- 5
management theory (Haselton & Buss, 2000) by presenting a mathematical derivation of the
model, broadening its potential domains of application, and presenting new predictions. We
eter explaining the direction of biases is the relative effects on fitness of
the d
e circumstances
ancestral past,
thus providing guidance about where we should expect to find the classic biases, such as the
fundamental attribution error, and their exceptions, and where as yet undiscovered biases may be
found. Equally important, this perspective speaks to the ongoing debate about human rationality
by demonstrating that a design flaw of human cognition;
be a design feature.
Noise and Uncertainty
The world of the perceiver is filled with uncertainty. In social inference, a judge must
overcome the fact that a target’s behavior is determined by multiple factors, many of which
eiver and target
by competing interests, important social clues may
be c eception. Social
ecause they
occurred in the past or might happen in the future.
These difficulties are not limited to social domains. The fact that in complex
environments perception is always clouded by the presence of confounding noise was central to
the development of signal detection theory in psychophysics (Green & Swets, 1966). All forms
argue that a key param
ifferent types of error.
This effort toward integration is useful because it provides clues about th
in which reasoning in a biased way may have yielded fitness advantages in the
biased reasoning need not be deemed
instead it may often
Error Management and Adaptive Bias
interact in complex ways to produce behavioral outcomes. Moreover, if the perc
are engaged in strategic interaction, marked
oncealed or a target might stage interference by engaging in active d
judgment and inference may also concern events that are not directly observable b
The Paranoid Optimist -- 6
of judgment under uncertainty will be prone to errors. Given the necessary existence of these
errors, how should systems best be designed? Error management theory provides a potential
Erro
signal
o understanding how
natural selection engineers psychological adaptations for judgment under uncertainty. In
general, there are four possible outcomes consequent on a judgment or decision. A belief can be
adopted when it is in fact true (a true positive or TP), or it can not be adopted and not be true (a
r (FP) occurs when
curs when the
s. A false
positive occurs when the subject does something though it doesn’t produce the anticipated
benefit, and a false negative when the subject fails to do something that, if done, would have
provided a benefit.
nsidered more
, scientists bias
type II errors,
because reducing type I errors necessarily increases type II errors. The reverse asymmetry
characterizes hazard detection. Misses (false negatives) are often much more costly than false
alarms (false positives). This asymmetry holds for humanly engineered devices such as smoke
answer.
r Management Theory
Error management theory (Haselton & Buss, 2000) applies the principles of
detection theory (Green & Swets, 1966; Swets, Dawes, & Monohan, 2000) t
true negative or TN). Then there are two possible errors. A false positive erro
the subject adopts a belief that is not in fact true, and a false negative (FN) oc
subject fails to adopt a belief that is true. The same framework applies to action
The costs of the different outcomes, and in particular the two types of error, are rarely
identical. In testing hypotheses, type I errors (false positives) are typically co
costly by the scientific community than are type II errors (false negatives). Thus
their decision-making systems (e.g., classical inferential statistics) toward making
The Paranoid Optimist -- 7
detectors and for evolved hazard detectors such as anxiety, stress, and cough (Nesse, 2001), and
hazard-detection systems are often biased toward false alarms.
ems should be
rror rates,
ets, 1966; Swets,
n-making
adaptations have evolved through natural selection to commit predictable errors. Whenever there
exists a recurrent cost asymmetry between two types of errors over evolutionary time, selection
will fashion mechanisms biased toward committing errors that are less costly in reproductive
the two types of
T predicts
that human psychology contains evolved decision rules biased toward committing one type of
error over another. In the following sections, we demonstrate how this model can account for a
large number of biases that have been observed empirically. First, though, we derive the central
(Green and
e belief (for
x is sexually
ative scale,
giving essentially the same results, but here we consider only cases where there is a dichotomous
choice to form a belief or not do so. The belief in question need not be a conscious one. By
‘adopting a belief’ is meant behaving or reasoning as if the corresponding proposition were true.
Whenever the costs of errors are asymmetrical, humanly engineered syst
biased toward making the less costly error. This bias sometimes increases overall e
but, by minimizing the more costly error, it minimizes overall cost (Green & Sw
Dawes, & Monohan, 2000). According to error management theory, certain decisio
currency.
Because the human environment is often very uncertain, and the costs of
errors are likely to be recurrently asymmetric in most fitness-relevant domains, EM
claims of EMT formally, using a simple model based on signal detection theory
Swets 1966). Consider the situation where the subject might or might not form som
example, that there is a snake in the grass, or that a member of the opposite se
interested in him). The approach can be extended to cover judgements on a quantit
The Paranoid Optimist -- 8
Let us call the state of the world that may or may not obtain lower case s, whereas the
belief that the subject may form is capital S. That is to say, a subject with belief S believes that
there are four
s formed and
t formed, and
ormed (S
and ¬s), whereas a false negative would represent the failure to form a belief which is in fact true
(¬S and s).
The signal detection problem is the problem of how much evidence for the state s to
e to specify the
of that
ro, then there is
some uncertainty in the world. That is, the observed evidence could have been generated if the
world is in state s or in state ¬s . If this uncertainty is not present, then the signal detection
problem is trivial and there is no scope for the evolution of bias according to our formulation.
s) is greater than
are equal, and the
966, p. 23). The
he relative
probability that s is in fact the case given the observed evidence e increases. An unbiased
decision would mean adopting S wherever the likelihood ratio is greater than 1. Any other
threshold is a bias; a bias against S if it is greater than 1, and a bias towards S if it is less than 1.
the world is in state s, which may or may not really be the case. As detailed above,
possible outcomes in such a situation. A true positive would be where the belief wa
was in fact true (that is, S and s). A true negative would be where the belief was no
was not true (¬S and ¬s). A false positive would be where the belief was erroneously f
require before adopting the belief S. For every degree of evidence e, it is possibl
probability of that evidence being observed if s, or p(e|s), and also the probability
evidence being observed if ¬s, or p(e|¬s). If both p(e|s) and p(e|¬s) are non-ze
Intuitively, it would seem that the subject should form the belief S if p(e|
p(e|¬s). This is indeed an optimal rule if the a priori probabilities of s and ¬s
organism’s goal is to maximize the number of true beliefs (Green and Swets 1
ratio p(e|s)/ p(e|¬s) is called the likelihood ratio. As the likelihood ratio increases, t
The Paranoid Optimist -- 9
From an evolutionary perspective, a decision rule is optimal not if it maximizes the
number of true beliefs, but if it has the best possible effect on the organism’s fitness. Let us
e effect on
hen ¬s is in
FP is the payoff for a baseless belief S. vFN is the effect of believing ¬S when s is
actu
The expected value of any decision is given by the following expression:
assume that the four possible outcomes have different effects on fitness. vTP is th
fitness of believing S when s is in fact the case; vTN is the effect of believing ¬S w
fact the case. v
ally the case.
}
{
}{
s)vFP|p(S s)vTN|Sp()(s)vFN|Sp( s)vTP|p(S)(
¬
+
¬
¬
¬
+
¬
+
= spspEV (1)
f the
a true
negative times the payoff for a true negative, the probability of a false positive times the payoff
for a false positive, and the probability of a false negative times the payoff for a false negative.
The optimal decision rule would be one that maximized expression (1). It can be shown that (1)
is maximized by adopting the belief S wherever there degree of evidence is equal to e, where:
The burden of expression (1) is simply that the expected value is the sum o
probability of a true positive times the payoff for a true positive, the probability of
)()(s)|( vFPvTNspep +
¬
=
For economy, we do not provide a derivation of this expression in this paper, but is given
in full in Green and Swets (1966, pp. 21-23). The left-hand term is the likelihood ratio of s given
the evidence e, and the right-hand term is made of up of the relative frequencies of s and ¬s, and
the payoffs for the four possible outcomes. Equation (2) has the satisfying property that if s and
)()(s)|( vFNvTPspep +¬
(2)
The Paranoid Optimist -- 10
¬s are equally likely a priori and the payoffs for all the possible states are equal, then the subject
should believe S if p(e|s) is greater than p(e|¬s), as intuition would predict.
fferent
inciple vary
d vTN constant and
tcome,
including opportunity costs, caused by the two types of error. As long as the errors are measured
in relation to the value of the true outcomes, and all payoffs are expressed in the same currency,
no information is lost by this, and it means that only the costs of the two error terms need be
ion example
e conceptualized in
term hus the model
can hold vTP and vTN constant and vary only vFP and vTN without loss of information.
First, consider the case where the cost of a false positive is rather small, and that of a
false negative is rather large. This would be the situation, for example, for an animal detecting a
way when in fact
ing a potentially
to 50 units.
unt of sensory evidence available, but that evidence is uncertain. For
example, a stick has many of the properties of a snake. The question is how much evidence to
require that the perceived object must belong to the class of snakes not the class of sticks before
assuming that it is a snake.
The type of case central to this paper is that in which the payoffs for the di
outcomes are not all equal. Though there are four payoffs to consider, that can in pr
independently, the situation can made conceptually clearer by holding vTP an
equal, and defining vFP and vFN as the payoff of the deviation from the optimal ou
considered in making predictions. For example, in the female investment-detect
used below, the vTP is substantial (value of male investment), but this may b
s of vFN as an opportunity cost (cost of missing out on male investment); t
snake. The payoff for a false positive would be the wasted energy of moving a
there was no danger – say 1 unit. The payoff for a false negative would be allow
venomous snake too close. This negative effect of this could be very large – say 1
There is a certain amo
The Paranoid Optimist -- 11
Assume for convenience that p(s) = 0.1 and p(¬s) = 0.9 – that is, there are nine times as
many sticks as snakes in the world. This assumption is arbitrary, but it affects only the scaling
nstant. Figure 1
conditions, with
a large
In fact, when
snakes are rare and not very dangerous, there is a bias against detecting them, since the optimum
threshold is greater than 1. However, as vFN increases in magnitude, the optimal threshold for
adopting S very rapidly declines. At vFN=-10, the optimal point is at 0.82, which is a bias
should adopt S
l costs to fitness are
still en multiple
false positives. It is far better to see a snake where there is only a stick than vice versa.
This first example illustrates the ‘smoke detector principle’ (Nesse, 2001, 2005)—if the
cost of failing to detect something is relatively high, it is best to have a lot of false alarms if it
ssibility.
st-
positive, and a
, let us say -5.
However, the value of the false positive is potentially higher (very costly), since if she mates and
then is deserted she faces the possibility of raising an offspring alone, and may have trouble
finding another partner in future. Thus vFP varies from -1 to -50. We assume 40% of all men are
deserters. Again this is an arbitrary assumption that affects only the scaling.
and not the shape of the relationships to be shown, since p(s)/p(¬s) is always a co
plots the optimal point at which the subject should adopt belief S under these
vFN varying from -1 to -50. When vFN is very small, the organism should require
likelihood ratio to adopt S, because if it does so it incurs the cost of moving away.
towards detecting snakes. At vFN= -50, under optimal behaviour, the individual
even though ¬s is over 5 times more likely than s given the evidence. Tota
minimized, because the rare false negative is so much more damaging than ev
means catching the real event when it does happen. Let us also consider another po
Imagine a female trying to detect whether a male is willing to make a significant po
reproductive investment if she mates with him. The value of this investment is
false negative involves missing out on it, so the opportunity cost vFN is significant
The Paranoid Optimist -- 12
Figure 2 shows the optimum threshold as vFP varies. If the cost of being deserted is low,
the female should have a bias towards accepting the evidence for male commitment. However, as
s that she
n generated by
ihood of s is more
e model
predicts the phenomenon of ‘commitment skepticism’, which has been empirically documented
by Haselton and Buss (2000). (We discuss this example and the research evidence for it in more
detail below.)
objective
e suggests,
es not restrict
the conclusions that can be drawn, since the payoff of a veridical outcome can always be restated
as an opportunity cost of the converse error, and vice versa. The optima generated by a signal
detection model will be influenced by the a priori probabilities of the two states of the world, and
e distribution
esse 2001, 2005,
rinciple’;
see Swets, Dawes, & Monahan, 2000, for applications in diagnostic domains). Our central
result is robust to permutations of these other parameters: where the relative costs of the two
errors are asymmetric, the optimal thresholds are biased away from 1 and towards the less costly
error.
the cost of desertion increases, the optimum threshold soon exceeds 1, which mean
should not adopt S even when the available evidence is more likely to be have bee
s than ¬s. If vFP = -30, then she should not accept S unless the objective likel
than four times that of ¬s given the evidence she has been able to observe. Thus th
The model clearly shows that the optimal decision rule is based not on the
likelihoods alone, but also on the payoffs of the different outcomes. EMT, as its nam
deals specifically with the relative costs of the two errors, FP and FN, but this do
also by the how well the evidence discriminates between the two states (that is, th
of the likelihood ratio). However, we do not explore those dynamics here (see N
for some further exploration of these models in the context of the ‘smoke detector p
also
The Paranoid Optimist -- 13
Applications of EMT
We review three somewhat overlapping classes of biases. Our classification system is
lly exclusive
o possible errors
he less costly
ecision makers also face a significant degree of uncertainty about the true
probability of an event.
Protective Effects in Perception, Attention, and Learning
Few failures are as unforgiving as failure to avoid a predator.
a & Dill, 1990)
the perception of
t the source of
the sound is approaching the listener. In a series of psychoacoustical experiments involving
speakers moving on cables, Neuhoff and colleagues demonstrate that sounds rising in intensity
are perceived as approaching faster than matched sounds that are falling in intensity (see
tant falling
, it is better to
hanisms that
n is
compatible with the error management model. Natural environments are filled with competing
sources of sound that render auditory judgments susceptible to error. For approaching sounds,
the relatively inexpensive false positive error would be to take preparatory action for an arriving
sound source too early. The false negative would be to take such action too late, which could
intended to provide a heuristic organizing scheme, rather than an exhaustive, mutua
taxonomy. We argue that each case is an example of error management. The tw
are plausibly asymmetrical in cost, and in each case, the bias is towards making t
error. In each case, d
(Lim
Auditory Looming. Neuhoff (1998, 2001) shows that there are biases in
sounds that are rising and falling in intensity. Rising intensity is usually a cue tha
Neuhoff, 2001, for a review). Moreover, they are judged to be closer than equidis
sounds. Neuhoff proposes an adaptive explanation; when a source is approaching
be prepared for it too early than too late, and so selection would favor neural mec
detect approaching sounds in manner asymmetric to receding ones. This explanatio
The Paranoid Optimist -- 14
well lead to such costly outcomes as being struck by a projectile, predator, or assailant. Thus, the
optimal system is biased toward false positive errors. This is the familiar principle of the smoke
if the cost is
92). We will
gue that a whole host of biases fall into this same, self-protective smoke detector class (table
1).
Allergy, Cough, and Anxiety. Nesse (2001, 2005) argued for the ‘smoke detector
principle’ in bodily systems designed to protect from harm. Nesse describes medical examples
such as allergy and cough where a protective system is often mobilized in the absence of real
drugs or
01). Psychological
on with things
likely to have been dangerous in the ancestral environment, such as spiders, snakes, and
potentially dangerous persons, as we discuss below (Mineka, 1992; Seligman, 1971; Tomarken,
et al., 1989). A tendency for anxiety mechanisms to produce false positives is a plausible
01).
etically prepared
dence
erous animals, but
also biases that serve to elicit fear, maintain it, and express it more often than it is needed.
Mineka and colleagues have demonstrated that snake fear responses are more easily acquired and
more difficult to extinguish than fears of other fear-relevant stimuli (see Mineka, 1992, for a
review). Even when extinction is successful, it tends to be short-lived, as the fears are easily
detector: it is better to tune a smoke detector to always detect a genuine fire, even
the occasional false alarm (Nesse, 2001, 2005; also see Bouskila & Blumstein, 19
ar
threat. These defense systems appear to be over-responsive; dampening them with
treatment actually results in few untoward effects on the subject (Nesse, 20
defense mechanisms such as anxiety are also easily evoked, especially in connecti
explanation for the observed prevalence of phobias and anxiety disorders (Nesse, 20
Dangerous Animals. It has long been argued that humans are phylogen
to produce a fear response to snakes and spiders (Seligman, 1971). More recent evi
suggests not only a special sensitivity to acquire fears of these ancestrally dang
The Paranoid Optimist -- 15
reacquired (Mineka, 1992). In experiments, people overestimate the covariation between electric
shocks and images of snakes and spiders but do not overestimate the covariation between shock
rical outlets (de Jong
). The
(Tomarken et
quency in an
experiment, low-fear individuals also exhibit the covariation bias effect (Tomarken et al., 1989,
also see deJong & Merckelbach, 1991). Once a negative association with snakes and spiders is
established in a person’s mind, the fear response can be evoked by a much briefer presentation of
993).
s, and the
ceived of as a
bias—snake and spider fears are acquired on the basis of slimmer evidence than are fears of
other dangerous objects, even those that in contemporary terms are much more dangerous, such
as electrical outlets, guns, and automobiles. In ancestral environments, the over-expression of
y, whereas failing to fear truly
dang severely venomous
velop similar
Dangerous Persons. It is quite possible that the greatest threat to life in ancestral
environments was other people. In modern environments, from traditional societies to
industrialized nations, groups regularly wage deadly wars on one another (Keeley, 1996), young
adult men who are at the peak stage of intrasexual conflict commit a disproportionate number of
and images of flowers or mushrooms, or even with images of damaged elect
& Merckelbach, 1991; Tomarken, Sutton, & Mineka, 1995; Tomarken et al., 1989
covariation bias effect appears to be strongest in people with specific animal fears
al., 1995), but when the fear-relevant stimulus (e.g., snake photos) are raised in fre
the feared image than is required for pictures of other stimuli (Oehman & Soares, 1
Thus, there appear to be biases in expressing fears of snakes and spider
specialized sensitivity that facilitates the acquisition of these fears may also be con
fears of snakes and spiders was inconvenient but not overly costl
erous animals would have been extremely costly, given the presence of
snakes and spiders in tropical regions. Bouskila and Blumstein (1992) de
expectations about estimations of predation hazard in non-human animals.
The Paranoid Optimist -- 16
murders, and competing reproductive interests result in spousal homicide (Daly & Wilson,
1988). Thus, a parallel analysis to that advanced for dangerous animals applies to dangerous
sed in a biased
es capture attention
em.
capture attention
for longer and cause more task interference than words describing neutral or positive traits. In
practice, the extremely undesirable traits are things that evoke interpersonal threat or violence,
such as hostile, mean and sadistic. Thus, these effects may result from the operation of a threat
stimuli.
behavior, such
ents, racial
and ethic cues appear to activate the psychology of inter-group conflict (Kurzban, Tooby, &
Cosmides, 2001; Sidanius & Veniegas, 2001). The assumption that members of one’s own racial
or ethic group are more generous and kind (Brewer, 1979), and less hostile and violent than out-
an error
rs are
ntentions on
w, especially
for members of competing coalitions. This asymmetry did not characterize inferences about in-
group members, in which costly within-coalition conflict would have resulted from unwarranted
inferences of hostility or aggressiveness. Consistent with this analysis, ambient darkness—a cue
signaling increased risk of hostility from others—increases racial and ethic stereotypes connoting
persons. There is evidence that cues of interpersonal threats also tend to be proces
fashion. For example, Fox, Russo, and Dutton (2002) showed that angry fac
for longer than happy or neutral faces, even when participants are trying to ignore th
Similarly, Pratto and John (1991) found that words describing undesirable traits
detection system that is predisposed to bias attention toward ancestrally dangerous
In ancestral environments, between-group differences in appearance and
as tribal markers, signaled differences in coalition membership; in modern environm
group members (e.g., Quillian & Pager, 2001), is a bias that can be understood from
management perspective. Inferences about relatively unknown out-group membe
uncertain. For ancestral humans, the costly false negative was to miss aggressive i
the part of others, whereas the false positive of over-inferring aggressiveness was lo
The Paranoid Optimist -- 17
violence, but has little effect on other negative stereotypes (e.g., laziness or ignorance) (Schaller,
Park & Faulkner, 2003; Schaller, Park & Mueller, 2003).
estion of a
d (Garcia, Ervin
of specialized
st of a lost
source of calories. As with snake fears, taste aversions are long-lived and hard to extinguish.
Only taste and smell cues are effective at creating an aversion (auditory or visual cues are
generally ineffective, Rozin & Kalat, 1971). And, in contrast to other conditioned associations,
alaise can be
orous animals
e aversions is lost in
a species that relies on only one food that is always fresh as it is drunk straight from a live host:
vampire bats (Ratcliffe, Fenton, & Galef, 2003). The ease with which food aversions are
acquired and maintained, given relatively slim evidence of their toxicity, results in many false
version to a
ay mean missing out for an
enti low compared to
the cost of eating a potentially fatal toxin or pathogen (a mistake one can make only once!), so
the system is biased towards self-protection rather than calorific maximization.
Several other food choice phenomena are illustrative. Children, who are less able than
adults to detoxify poisonous plant parts, tend to avoid leaves and vegetables and are notoriously
Food Aversions. A single instance of gasterointestinal malaise following ing
particular food is sufficient to induce a strong, long-lasting, avoidance of that foo
& Koelling, 1976; Rozin & Kalat, 1971). These aversions are likely the product
associative biases designed to help organisms avoid ingesting toxins, even at the co
creating the aversion requires only one trial and the delay between ingestion and m
quite prolonged (Garcia et al., 1966). These associative biases characterize omniv
for whom they would be most beneficial; the ability to form conditioned tast
alarms—avoiding foods which are in fact safe.
Within the EMT framework, the false positive is the formation of a taste a
food that is normally harmless. This has a non-trivial cost, since it m
re lifetime on an available source of nutrition. On the other hand, this cost is
The Paranoid Optimist -- 18
picky about what they eat (Cashdan, 1998). Pregnant women, whose immune system is
suppressed in order to avoid attacking the fetus, develop a variety of pregnancy-specific food
nstrate, even the
r disgust.
ainer labeled “table
atched the
experimenter fill both bottles from the same box of Domino sugar (Rozin, Markwith, & Ross,
1990). Likewise, people refuse to eat otherwise tasty food products that are presented in the
shape of a disgusting substance, like fudge in the shape of dog feces (Rozin & Fallon, 1987).
tion to avoid
omeone is safe
or example,
although people understand that mere contact is insufficient for the transmission of AIDS, they
physically distance themselves from AIDS victims, demonstrate dose insensitivity by expressing
discomfort with even 5 minutes of contact, and exhibit backward contagion as evidenced by
orn by an AIDS
, Cantu, & Rittiman,
ce may be
nomalies
(e.g., obesity) as if they are produced by contagious disease. The error management
interpretation of these phenomena is that the costs of false negatives (failing to avoid someone
with a contagious disease) is high, whereas the cost of a false positive is relatively low (avoiding
contact with a non-contagious person), so disease avoidance mechanisms will be over-inclusive
aversions (Fessler, 2002). As clever experiments by Rozin and colleagues demo
mere suggestion that a food might be contaminated is sufficient to elicit avoidance o
When given a choice between two containers of sugar, people opt for the cont
sugar” over the one marked “NOT sodium cyanide” even though they had just w
Avoiding the Ill. People may require little evidence of illness or contamina
someone, whereas much stronger evidence is required warrant the inference that s
or free from disease (Kurzban & Leary, 2001; Park, Faulkner, & Schaller, 2003). F
discomfort with the thought that an item of clothing they once wore would be w
victim in the future (Rozin, Markwith, & Numeroff, 1992; Bishop, Alva
1991). As we discuss below in the implications of EMT section, disease avoidan
broadly over-inclusive and people may also treat other disabilities or pheonotypic a
The Paranoid Optimist -- 19
and will express many false alarms. This may account for the difficulty in reversing stigmas
associated with both contagious and non-contagious physical afflictions (Bishop et al., 1991) as
ess might also
rrational local panic associated with outbreaks of SARS and Mad Cow
Biases in Interpersonal Perception
Interpersonal perception is notoriously prone to bias and error. We propose that many of
these documented biases can be interpreted within the framework of error management theory
xplain one of
es to falsely
assume that an intentional agent (e.g., another human) has caused some event is less costly than
to miss this fact. Given that agents often have interests that compete with those of the perceiver,
it is important to have a low threshold for inferring their presence. For example, if one
e proposes that it
gent was responsible
t’s presence,
ropose that
belief in gods may be a by-product of this adaptive bias. The proposed animacy bias is
consistent with classic laboratory experiments conducted by Heider & Simmel (1944; see also
Bloom and Veres, 1999). When participants view moving images of circles and squares, they
find it difficult not to infer intentional states—chasing, wanting, and escaping. The tendency to
compared with more easily manipulated social stigmas (such as those surrounding
homosexuality, Kurzban & Leary, 2001). This form of defense over-responsiven
explain the seemingly i
disease in far away places.
(table 2).
The Illusion of Animacy. Guthrie (2001) uses error management logic to e
the key features of religion—animism. He proposes that in ambiguous circumstanc
encountered a collection of twigs arranged in an improbably neat array, Guthri
would be better to entertain the thought that a human or other intentional a
for the arrangement, and to increase one’s vigilance to the possibility of the agen
than to casually ignore it. Guthrie (2001) and Atran and Norenzayan (in press) p
The Paranoid Optimist -- 20
infer intentional states in these stimulus arrays emerges early (age 4), and there is preliminary
evidence of cross-cultural universality of the bias (in Germans and Amazonian Indians, Barrett,
ly be variable.
on across cultures (Atran & Norenzayan, in press) are also consistent
with
e Forgiveness
Bias. The sinister attribution error is ego’s assumption that relatively trivial aspects of another’s
behavior indicate negative thoughts or intentions towards ego (Kramer, 1994, 1998). EMT would
predict that such a bias could arise where the costs of failing to detect negative evaluations that
are none in
paranoid cognition are exhibited
diffe tus within an
organization (see Kramer, 1998 for a review; also see Fenigstein, 1984).
In one sinister attribution study, first and second year students in a masters program at a
prestigious business school were asked how they would interpret ambiguous interactions with
if they made an
rn, or if they
ptly rose and left
et the
interactions in a “personalistic” fashion by inferring that their call was not returned because the
recipient did not wish to speak to them or that the person found their joke boring (rather than
inferring, for example, that their phone message was never received). This effect was amplified
when first year students imagined that the interaction took place with a second
year student,
Todd, Miller, & Blythe, in press), though its magnitude of expression may certain
Common features of religi
a universal animacy bias.
The Sinister Attribution Error, Overweighting of Social Gaffes, and Negativ
in fact do exist are higher than the costs of inferring such evaluations where there
reality. Kramer has shown that the sinister attribution error and
rentially by people under intense scrutiny, new to social groups, or low in sta
their fellow students. They were asked, for example, what they would infer
urgent phone call the evening before an exam that their fellow student did not retu
were telling a joke they thought was funny and one of their fellow students abru
the table. First year students were more likely than second year students to interpr
The Paranoid Optimist -- 21
whereas second year students did not make differing attributions depending on the status of the
person they imagined interacting with. In a second study with the business students, Kramer
fellow
se who believed that
deotaped
e to their fellow students than those who did not believe
they were under scrutiny (Kramer, 1994).
Savitsky, Epley, and Gillovich (2001) documented related effects. Participants
committed an experimentally-induced social gaffe—failing at a “simple” anagram test or being
n embarrassing manner. In four studies, the participants believed that they were
judg ers than they
In sum, when individuals are new to social groups or feel that they are under scrutiny,
they become hypervigilant to the negative thoughts, intentions, or evaluations of others. These
situations resemble ancestral environments where failing to detect negative social evaluations
was w village.
ct aggression,
5).
in press) found
that men and women underestimated the degree to which their partners had forgiven them after a
transgression (e.g., insults, flirtation with others). With transgression severity controlled, this
bias was strongest in partnerships characterized by less relationship satisfaction. Thus, as the
investigated whether participants in an economic coordination game believed their
participants were trying to sabotage them in order to earn more money. Tho
their reactions in the game revealed managerial skill and that they were being vi
attributed a greater desire for sabotag
described in a
ed as less intelligent and less favorable in their general impression by strang
actually were.
highly costly, such as when entering into a new coalition or moving into a ne
Failing to detect negative intentions or evaluations could result in ostracism or dire
and the consequences could literally have been deadly (Baumeister & Leary, 199
In the context of romantic relationships, Friedman, Fletcher, & Overall (
The Paranoid Optimist -- 22
researchers proposed, a negative forgiveness bias may help to ensure that transgressions are fully
mended or not further exacerbated, especially in relationships that are already on the rocks.
rs, people are
ption that a person’s
gically
, 1977). The
extent to which this bias is expressed varies between collectivist and individualist cultures with
members of collectivist cultures tending to qualify dispositional inferences by referencing the
social context to a greater extent than members of individualist cultures (Choi, Nisbett, &
ed, members of
ces to the same
any of our
initial social judgments are designed to help us avoid poor social exchange partners. This is
important because humans depend on social exchange based on reciprocity to a very great extent,
and reciprocity is always vulnerable to cheating. Thus, it is plausible to argue that avoiding
ides, 1989).
oid social
ause it entails
interaction. This aspect
of the FAE can be interpreted from an error management perspective (see Andrews (2001) for
this and other, complementary explanations of the various manifestations of the FAE). The false
negative is to assume that a person’s behavior is not representative of their long-term
dispositions, and thus not take it into account in future interactions. The risks of the false
The Fundamental Attribution Error. When interpreting the behavior of othe
prone to making the fundamental attribution error (FAE), which is the assum
behavior corresponds to their underlying dispositions to a greater extent than is lo
warranted (e.g., Andrews, 2001; Nisbett, Caputo, Legant, & Marecek, 1973; Ross
Norenzayan, 1999). When situational and dispositional inferences are disentangl
both collectivist and individualist cultures tend to display dispositional inferen
degree (Norenzayan, Choi, & Nisbett, 2002). Kurzban & Leary (2001) argue that m
social cheaters has been a major selective pressure on human social cognition (Cosm
One effect of the fundamental attribution error is to cause observers to av
exchange partners who have once demonstrated some negative social behavior, bec
the assumption that the person is disposed to do the same again on repeat
The Paranoid Optimist -- 23
negative are becoming involved with a person who has social cheating tendencies. The false
positive is assuming someone is anti-socially disposed because of a behavior, which did not in
re transient
eople who
ate social partners. This cost might be significant, but often not as high
as th
A recent series of studies is consistent with this interpretation of the FAE. One of the
original demonstrations of the FAE showed that people infer the existence of more personality
traits in others than they do in themselves (Nisbett et al., 1973). Using similar methods, Burkett,
E occurred for
tive trait
tigated, traits
related to social exchange (dishonesty, cheater, liar, and deceitful) were those for which there
was the largest FAE bias. In a similar vein, using the lexical decision paradigm, Ybarra, Chan,
and Park (2001) found that adults were faster to identify trait words connoting interpersonal
tile, cruel, disloyal) than words connoting poor skill (e.g., stupid, weak,
clum ed that people
ct themselves
The Social Exchange Heuristic. Standard economic principles predict that players in the
one-shot prisoner’s dilemma game should defect rather than cooperate. If one partner cooperates
while the other defects, the cooperator suffers a greater loss than if he or she had defected. The
interaction is not repeated, so there is no incentive to signal cooperativeness, and experiments are
fact represent his or her underlying dispositions, but was brought about by a mo
feature of the context. The cost of such a false positive might be the avoidance of p
would in fact be appropri
e cost of being exploited.
Cosmides, and Kirkpatrick (2003) demonstrated that this manifestation of the FA
negative traits such as dishonest, mean, rude, and inconsiderate, but not for posi
attributions such as honest, fair, kind, and intelligent. Of the negative traits inves
social costs (e.g., hos
sy), or positive qualities (e.g., honest, friendly, gentle). Ybarra (2002) conclud
tend to lean toward seeing the bad in others in “morality” domains in order to prote
from poor social partners.
The Paranoid Optimist -- 24
carefully devised so that there is no information about reputation that might serve to provide
clues about the partner’s cooperative disposition at the start of the game. Yet, cooperation often
erimental
; Caporael, Dawes, Orbell, & van der Kragt, 1989; Camerer & Thaler
1995
es results from
the operation of a social exchange heuristic (Yamagishi, Terai, Kiyonari & Kanazawa, 2003).
They propose that the costs of falsely believing one can defect without negative social
consequences are often higher than cooperating when one could safely defect. This asymmetry
(e.g., a low dollar
cism) are high. The
n which
cooperation is either highly valued or especially necessary. And, as predicted, in Japanese
collectivist samples where exchanges are often closed to outsiders, cooperation in one-shot
experiments is higher than in the more individualist United States samples (Yamagishi, Jin, &
or management
ility of repeated
tent. Thus, people
may be predisposed to expect negative consequences of non-prosocial behavior even when,
objectively, such consequences are unlikely to follow. The bias towards prosociality is the
subject of competing explanations which take quite different explanatory stances (Price,
Cosmides & Tooby, 2002; Gintis et al., 2002; Henrich & Boyd, 2001; Bowles & Gintis, 2002),
occurs in the one-shot prisoner’s dilemma game and in many other games in exp
economics (Sally, 1995
; Henrich et al., 2001).
Yamagishi and colleagues hypothesized that cooperation in one-shot gam
should hold when the costs of “unneeded” cooperation are relatively low
amount is lost) or when the social costs of failing to cooperate (potential ostra
costs of ostracism may be particularly high in interdependent social contexts i
Kiyonari, 1999).
We suggest that this bias can be conceptualized as a combination of err
and an artifact of modern living, since in an ancestral environment the probab
encounters would have been high and social reputation effects especially po
The Paranoid Optimist -- 25
and it is as yet unexplored whether these are complementary or competing accounts to the social
exchange heuristic.
that the
er evolutionary
icts that
ed. Haselton & Buss (2000) hypothesized a number of sex-specific
biases in interpersonal perception.
The reproductive success of males is ultimately limited by the number of females they
can inseminate, whereas for females there is no fitness return on increasing numbers of mating
e, 1996, 2000;
opportunity
ess is affected
by the continued investment of the male. Given these asymmetric costs and benefits, Haselton
and Buss argued that men would have adaptive cognitive mechanisms designed to avoid missed
mating opportunities, whereas women would have cognitive mechanisms designed to avoid post-
d tend to overestimate
issing a sexual
ual interest
where there is none). A number of empirical studies demonstrate that men do indeed
overestimate women’s sexual interest. In laboratory studies, when male partners in previously
unacquainted male-female dyads are asked to infer their partner’s sexual interest, they
consistently rate it as higher than the female partner’s report suggests, and higher than the ratings
Sex-Differentiated Biases in Decoding Courtship Signals. To the degree
problems of judgment and social inference differed for the men and women ov
history, or were associated with different cost asymmetries for the sexes, EMT pred
biases will be sex differentiat
partners beyond a certain point (indeed additional matings may become costly, Ric
Symons, 1979). Thus, for males there is a higher cost to missing out on a mating
than there is for females. For females, becoming pregnant is highly costly, and fitn
reproductive desertion.
The error management predictions in this case are that men shoul
the sexual interest of women with whom they interact, since the false negative (m
possibility that was in fact real) is more costly than the false positive (inferring a sex
The Paranoid Optimist -- 26
provided by female third-party viewers of the interaction (Abbey, 1982; Saal, Johnson, & Weber,
1989). A similar effect occurs in studies using photographic stimuli (Abbey & Melby, 1986;
ettes (Abbey &
surveys of
f sexual
ception does not appear in women (Haselton, 2003; Haselton & Buss, 2000; Maner et al.,
in press).
For women, in considering the commitment intentions of a potential partner, the false
negative would be to miss signs of a genuine desire to commit. The false positive, on the other
e or none. A
investing father,
ath (Hurtado &
Hill, 1992). This error could also reduce her future mating potential because it decreases her
residual reproductive value (Buss, 1994; Symons, 1979). Thus, EMT predicts a bias in women
towards underperception of men’s commitment intentions. Laboratory studies confirm that in the
tential
f commitment and
them to indicate
and men’s ratings
of a third-party man’s dating behaviors, demonstrating that the effect is not attributable to a
simple self-other rating difference which might result from participants’ concerns about self
presentation (Haselton & Buss, 2000). Importantly, evidence of commitment bias does not
appear in men’s assessments of women’s behaviors (Haselton & Buss, 2000).
Maner et al., in press), videos (Johnson, Stockdale, & Saal, 1991), short vign
Harnish, 1995), ratings of courtship behaviors (Haselton & Buss, 2000), and in
naturally occurring misperception events (Haselton, 2003). Importantly, evidence o
overper
hand, would be assumption of a willingness to commit where in fact there was littl
woman making this error could be forced to raise a child without the help of an
which in extant traditional societies can more than double the risk of offspring de
courtship context women underestimate men’s commitment. Women infer that po
indicators of men’s desire for a committed relationship (e.g., verbal displays o
resource investment) indicate less commitment than men report that they intend
(Haselton & Buss, 2000). The same result appears when comparing women’s
The Paranoid Optimist -- 27
Self-Related Biases
Positive Illusions. Some of the best-known cognitive biases concern beliefs about the self
the self,
of events to a
by Taylor and
llusions’.
Since the time of the review, some debate has arisen about the pan-cultural status of the positive
illusions. In particular, members of East Asian cultures such as the Japanese and Chinese have
sometimes been found not to self-enhance, but rather to self-criticize (Heine, Lehman, Markus,
& K ik, Bond, &
apanese
participants self-enhance (Sedikides, Gaertner, & Toguchi, 2003), but do so in different ways.
The Japanese participants rated themselves as more positive than the mid-point on collectivistic
attributes such as ‘cooperative’ and ‘respectful’, but did not self-enhance on individualistic
everse pattern,
et this finding in
pressed in whatever domain
xce with the error
management account that we develop below, which suggests some ways in which cultural
differences could emerge. We return to this issue in the general discussion.
Taylor and Brown offer an explanation for the prevalence of the positive illusions that
tacitly contains an error management argument. They argue that positive illusions motivate
and the future. People have been shown to have unrealistically positive views of
unwarranted optimism about the future, and to believe that they control the flow
greater extent than is logically warranted. These effects were grouped together
Brown in their seminal review (Taylor & Brown, 1988), and dubbed ‘the positive i
itayama, 1999; Kitayama, Markus, Matsumoto, & Norasakkunkit, 1997; Y
Paulhus, 1998).
On the other hand, other investigators have found that both American and J
attributes such as ‘self-reliant’ and ‘unique’. American participants showed the r
and were actually self-effacing on the collectivistic traits. The authors interpr
terms of a universal propensity to self-enhancement, which is ex
e llence is rewarded in, in the local context. This interpretation would accord
The Paranoid Optimist -- 28
people to persevere towards goals that would be beneficial but which have an objectively low
probability of success (1988, p. 199). For example, HIV-positive men who are developing
re unrealistic, but
s (Taylor et al.,
nd Brown
l world is
very difficult, because situations do not recur with exactly the same parameters. The two possible
errors will lead to opposite behaviors; a false negative to passivity, and a false positive to over-
sanguine behavior, with projects taken on that do not succeed. EMT predicts that if the cost of
llusional positive
sed belief (see
tive outcome. It is
better to believe that you can get something desirable even if you can’t, as long as the cost of the
false alarm is low relative to the opportunity cost of missing out on a fitness-enhancing
opportunity.
e the positive
aracteristics of
when people
itive bias
disappears (Campbell, 1986). People are unrealistically optimistic about the probability that
fitness-enhancing outcomes such as finding an ideal partner and gaining professional status will
happen to them (Weinstein, 1980). They have been argued to be unrealistically optimistic (that
is, to underestimate the likelihood) of health problems (Weinstein, 1982), which at first would
symptoms of AIDS have beliefs about the controllability of the disease, which a
nonetheless serve to motivate them towards active health-promoting behavior
1992). Nettle (2004) provides a more formal evolutionary model of the Taylor a
argument. Accurately assessing the likelihood of obtaining some outcome in the rea
trying and failing is low relative to the potential benefit of succeeding, then an i
belief is not just better than an illusional negative one, but also better than an unbia
figure 1 and table 2). This is the smoke detector principle applied to a posi
The EMT approach does indeed seem to account for the domains wher
illusions occur. People have unrealistically positive views of precisely those ch
themselves which are desirable or beneficial (Brown, 1986; Campbell, 1986), and
judge third parties and thus derive no potential benefit from enhancement, the pos
The Paranoid Optimist -- 29
seem opposite of what an error management account would predict. However, our interpretation
of this phenomenon is that people are unrealistically optimistic about their effectiveness of their
ylor et al.,
void health difficulties that are
inev
itivity to
potential harms coming from outside, and excessive optimism about benefits that can be obtained
by the self – predict that reasoning in domains controlled by the self may display different biases
to reasoning in domains beyond the self’s control. This is the essence of the paranoid optimism
self. There are
meta-analysis
lieve that their
own life is getting better, while also believing that life in general in the country where they live
is getting worse (Hagerty, 2003). Similarly, people feel they are less likely than average to be
involved in an automobile accident when they are the driver, but not when they are the passenger
ting predictions for
ness, people judge
ranted,
resulting in the so-called illusion of control (Alloy & Abramson, 1979; Langer, 1975; Langer &
Roth, 1975; Rudski, 2000; Vazquez, 1987). Given that the controlling behaviors in these
experiments are usually rather low cost (pressing a key, for example), it is a less costly error to
own efforts to avoid health problems (Taylor, Helgeson, Reed, & Skokan, 1991; Ta
1992). This makes sense from the EMT perspective, as trying to a
itable is a lower cost error than failing to avoid those that are avoidable.
The two different smoke detector biases predicted by EMT – excessive sens
phenomenon, predicting paranoia about the environment but optimism about the
phenomena in the literature which suggest such double standards. For example, a
of over 70 life satisfaction studies from 9 countries shows that people tend to be
(McKenna 1993). Such discrepancies are an area where EMT makes interes
further research.
The Illusion of Control. Finally, where events display some random
that their behavior has a greater influence on the flow of events than is in fact war
The Paranoid Optimist -- 30
continue the control behavior when it is in fact ineffective (the false positive) than it is to miss
out on the chance to control events (the false negative).
o first
s of its behavior,
e on the floor.
t had once
occurred before the delivery of food was ‘assumed’ to have caused the delivery of food. Very
similar effects can be demonstrated in humans, who when presented with actually random
patterns of reinforcement, develop superstitious beliefs about actions they must perform to
no, 1987; Rudski,
l that belief in
te (1994,5)
show that the result of uncontrollable reinforcement in a human conditioning paradigm is not
passivity or learned helplnessness, but instead, superstitious behaviour and a strong subjective
illusion of control. Only when explicit feedback of the non-effectiveness of the superstitious
ed helplessness
n been
easdale 1978), and
depr s (Alloy and
Abramson 1979, Vazquez 1987). Thus, the evidence suggests that superstitions and illusion of
control, though strictly speaking irrational, are healthy responses to an uncertain world.
In the ancestral environment, accurate information about the true contingencies between
people’s behavior and events around them, such as the movements of game animals, would have
Related to the illusion of control are superstitions. It was Skinner (1948) wh
showed that if a pigeon is given food reinforcement every 15 seconds, regardles
it may develop behavioral rituals, such as walking in a circle or rubbing its fac
Skinner’s explanation was in terms of adventitious reinforcement; a behavior tha
produce the desired contingency (Catania & Cutts, 1963; Matute 1994, 1995; O
2001). Such effects are not confined to the laboratory; naturalistic surveys revea
lucky charms and lucky tricks is widespread (Vyse, 1997). Experiments by Matu
behavior is provided does the illusion disappear, and under such conditions, learn
ensues. There is a conceptual link with depression here, since depression has ofte
explained in terms of learned helplessness (e.g. Abramson, Seligman and T
essed subjects are distinguished by the absence of illusion in control paradigm
The Paranoid Optimist -- 31
been scarce. As long as the cost of performing the superstitious behaviors was low relative to the
benefit of actually controlling events, EMT would predict cognitive mechanisms biased towards
superstition and the illusion of control to evolve.
Discussion
Ada
ses in cognition
are explained by the existence of asymmetric error costs and significant uncertainty. Thus, bias
in cognition is no longer a shortcoming in rational behavior, but an adaptation of behavior to a
complex, uncertain world. Biased mechanisms are not design defects of the human mind, but
the absence of bias
e of
t the mind is
equipped with multiple, domain specific cognitive mechanisms, with specific biases appropriate
to the content of the task and the particular pattern of costs, benefits and likelihoods. For
example, we are predisposed to fear spiders and snakes rather than elements of our contemporary
e are predisposed
act road traffic
more likely to kill us. We are prone to sex differences in the perception of
sexu han situational
causes. We are prone to believe that random events in the environment reflect the operations of
some unseen intelligence.
The existence of these biased systems is an important link between psychology and
culture. To persist in a culture, a pattern of information must capture the attention of individuals
ptive Biases
We have reviewed a large number of cases where apparently irrational bia
rather design features. In view of the content specificity of these effects, and
in many other types of cognition, a theory that held bias to be a generalized outcom
individual or cultural learning seems implausible. Rather, it seems likely tha
environment that are in fact much more dangerous, such as electrical outlets. W
to fear injured or diseased people and contamination of the food supply, when in f
and obesity are much
al intent, and to assume social non-reciprocation has dispositional rather t
The Paranoid Optimist -- 32
such that they will remember and pass it on. Those elements of culture best able to exploit the
inherent biases of the mind will have the greatest probability of being retained and transmitted.
rous serpents,
ound in the world’s cultures (Atran, 2002; Atran
; Guthrie, 2001).
Ope
Our argument is not that all of the biases we have described are produced by the same
cognitive mechanism, but rather than they have all been produced by the same evolutionary
mechanism, that is selection to minimize overall error costs, acting on many different cognitive
od aversions,
d require only
rospects, are
much more open to environmental influence. In one culture the relevant domain for positive
illusions might be hunting, in another success in college, and in still another, standing in the local
community. The cognitive system leaves open the flexibility for the individual to identify those
ilure is costly.
as snake and
es such as the
ibility of local
variation. Such variation might arise for several reasons. It might be that in a collective cultural
context, in which social rewards are contingent on cooperation and loyalty to the group, the
benefits to, for example, earning extra money are diminished. In as much as such cultures
disfavor individualists, there might actually be significant social costs to individual success in
In fact, tales of invisible gods who orchestrate the natural world, legends of dange
stories of plagues, and taboos about meat all ab
& Norenzayan, in press; Fessler, 2002
n versus Closed Developmental Systems
systems. Some of these systems are relatively closed. For example, the system of fo
or the predispositions to fear snakes and spiders, seems to have fixed content an
triggering by the environment. Other biases, such as optimism about future fitness p
domains in the environment where success yields benefits, and those where fa
We would predict that biases produced by relatively closed systems, such
spider fears, and food aversions, would show less cross-cultural variation. Bias
positive illusions, which are produced by open systems, would have the poss
The Paranoid Optimist -- 33
competitive affairs. In such a culture, the costs of the two errors would actually be different
compared to an individualistic culture, and so EMT would predict that positive biases would not
perate in a more
ast Asia
e to do with
lence in inter-individual competition. This is precisely the pattern found by Sedikides et al.
(2003).
Differential Evocation of Bias
In many domains ancestrally, asymmetries in costs varied depending on context. The
when they
otected. If moderating contexts were recurrent, consistent in
thei tations to respond
to them with variable degrees of bias.
We have already discussed several cases in which biases differ by context: sinister
attributions are more likely when people are new to social groups, negative forgiveness bias is
mor are enhanced
onments and
ias.
gh emotion.
Emotion states are activated in response to threats and opportunities and they may adaptively
channel us toward the specific thoughts and courses of action needed to respond to them
(Cosmides & Tooby, 2000). Maner and colleagues (Maner et al., in press) hypothesized that fear
would increase biases toward inferring aggressiveness in others, particularly members of
appear. Indeed, EMT would predict that if it is true that East Asian cultures o
collectivist way than Western ones, then the positive biases should be shifted in E
towards attributes related to excellence as a collective member and away from thos
excel
costs of missing threats are highest, for example, when individuals are vulnerable—
are sick, alone, or otherwise unpr
r effects, and signaled by reliable cues, we should expect judgmental adap
e common in relationships at risk, and aggressive stereotypes about outgroups
in the dark. In each of these cases, a cue that was present in both ancestral envir
today—new social partners, relationship discord, and darkness—shifts the b
A complementary way to understand adjustments of bias may occur is throu
The Paranoid Optimist -- 34
coalitional outgroups; sexual arousal, on the other hand, would increase men’s bias toward
overinferring sexual desire in women. They showed men and women clips of scary or
in
but were attempting
tral in
White, “saw” more
anger on male faces, especially the faces of outgroup (Black and Arab) males. The fear
manipulation had no effect on perceptions of sexual arousal in the faces. In the romantically
arousing film condition, men perceived greater sexual arousal in female faces, particularly when
ptions of sexual
ptions of
cific, and for
sexual arousal, sex specific. When fearful, men and women perceived greater threat from ethnic
outgroup members; when aroused, men but not women perceived greater arousal in attractive
opposite-sex faces.
in of disease-
lusive and respond
r.” They
when people are
fearful of contamination. European-American students who read a news clip about a local
hepatitis outbreak showed stronger associations between words like “disability” and “disease”
and between “disability” and “unpleasant” on the implicit association test, as compared with
controls (Park, Faulkner, & Schaller, 2003). In a subsequent study using the implicit association
romantically arousing films, and then asked them to interpret “micro-expressions”
photographs of people who had relived an emotionally-arousing experience
to conceal any facial expressions that would reveal it (the faces were actually neu
expression). In the fear condition, the study participants, who were mostly
the faces were attractive. The arousal manipulation did not increase men’s perce
arousal in other men’s faces, and the manipulation did not increase women’s perce
sexual arousal in any of the faces. Thus, the effects were emotion and target spe
Park, Schaller, and colleagues have documented parallel effects in the doma
avoidance. They proposed that adaptations for disease avoidance are overinc
noncommunicable phenotypic anomalies and even a target’s status as a “foreigne
demonstrated that biased associations of phenotypic cues with disease increases
The Paranoid Optimist -- 35
test, participants were exposed to slides evoking pathogen risk (germs lurking in a kitchen
sponge) or accidents (electrocution in a bathtub). Those who viewed the pathogen slides showed
e accident
rs found
participants.
immigration of
unfamiliar immigrant groups (Nigerians in one study and Mongolians in another) than familiar
immigrant groups (Scots and Taiwanese). In the accident condition, attitudes about these
immigrant groups did not differ (Faulkner, Schaller, Park, & Duncan, in press). According to the
also be expected
uctive
prevent rejection of the fetus, which shares only 50% of the mother’s
genes (Fessler, 2002); therefore we predict that pregnant women will experience enhanced
disease avoidance biases.
Some emotional and motivational states are chronically present in some people, and
m. In the micro-
world is a
oward a more
r et al, in
press). In the disease avoidance studies, individuals who scored high on an individual difference
measure of germ aversion or vulnerability to disease also showed stronger disability-disease
associations on the implicit attitudes measure (Park, Faulkner, & Schaller, 2003), greater dislike
greater associations between slides of obese people and disease than those in th
condition (Park, Schaller, & Crandall, 2004). Using related methods, the researche
similar effects concerning immigrant groups that were unfamiliar to their Canadian
Participants in the pathogen condition had more negative attitudes about allowing
logic of these studies, individuals whose immune systems are depressed might
show increased bias toward these groups. Pregnant women experience reprod
immunosuppression to
therefore biases moderated by these states will also reliably differ between the
expressions studies (Maner et al, in press), people who believed in general that the
dangerous place, saw more anger in male outgroup faces. People who tended t
promiscuous mating strategy saw more sexual arousal in opposite sex faces (Mane
The Paranoid Optimist -- 36
of fat people (Park, Schaller, & Crandall, 2004), and more negative attitudes about unfamiliar
immigrant groups (Faulkner, Schaller, Park, & Duncan, in press).
New
ficant
e two types
as, which will
be towards making the less costly of the two errors. Some of the effects we have reviewed were
predicted in advance using error management logic. These include commitment underperception
by women (Haselton & Buss, 2000), overinclusiveness of disease avoidance (e.g., Park et al.,
hi et al., 2003),
fundamental
attri been studied,
there may be many more that have not yet been the subject of empirical investigations.
We have already described several new predictions. We suggested that the personality
domains in which the FAE is particularly likely to occur will be those that are most likely to
tion we
occur will be
hat are
s. EMT also
predicts that discrepancies between judgments about outcomes the subject controls will often
show different biases to those not in the subject’s control, as in the result that people believe their
own life to be getting better but life in general to be getting worse. Such effects might be elicited
in many different domains. For example, in a simulation of the transmission of a disease, EMT
Predictions
EMT predicts the evolution of biases wherever the problem involves signi
uncertainty, has recurred and impacted fitness over evolutionary time, and where th
of error have reliably had asymmetrical cost. EMT also predicts the direction of bi
2003; Faulkner et al., in press), the use of the social exchange heuristic (Yamagis
negative forgiveness bias (Friesen et al., in press), and content effects in the
bution error (Burkett et al., 2003). Just as many such situations have already
impose fitness costs, such as aggressiveness and deceitfulness. In the previous sec
proposed that the cultural differences in the domains in which positive illusions
linked to cultural differences in the value of those domains. Qualities or outcomes t
universally valued, such as the preservation of health, will vary little across culture
The Paranoid Optimist -- 37
predicts that people should be overly fearful that others are infectious, but overly optimistic that
their own attempts to avoid contagion will be effective. We also suggested that pregnant women
will .
d courtship.
terest of others in
First, the
fitness costs of failing to recognize the interest of an interloper in one’s mate and to lose one’s
mate as a result are high. One must reinitiate mate search, pay new costs associated with
courtship and attraction, and risk the loss of investment from the mate in existing offspring. The
resenting
effect: a bias toward
threatening
situations. For example, at a cocktail party, if an attractive other behaves in a friendly and
animated fashion toward ego’s mate, ego will assume greater sexual interest on the part of the
other than will an independent on-looker. This bias would function, we propose, to increase
02) documented
mitted
ile) more
not involved in relationships. Maner and colleagues (Maner et al., 2003)
found that women in committed relationships showed a greater attentional and memorial bias for
attractive female faces than women not in relationships, providing additional suggestive evidence
of the interloper bias.
express disease avoidance attitudes that are especially strong or overinclusive
Haselton & Buss (2000) predicted two biases in the domain of sexuality an
We suggest two more. The first is a bias in inferring the romantic or sexual in
one’s mate and the second a bias in inferring the interest of one’s mate in others.
costs of somewhat elevated vigilance, especially if activated only in situations p
plausible threat, would be comparatively low. Thus we predict the interloper
over-inferring the sexual interest of others in one’s mate in ambiguous or mildly
mate retention efforts and help to ward off defection. Smurda and Haselton (20
evidence suggestive of the interloper bias. They found that people involved in com
relationships tended to rate the sexual interest of same sex others (e.g., based on a sm
highly than people
The Paranoid Optimist -- 38
Second, the fitness costs to a man of failing to detect partner infidelity are high. His own
reproduction can be delayed for the course of a pregnancy, at minimum. He also risks investing
costs of false
d time spent on
er fitness
us, there is a
delicate balance between the costs of errors in infidelity detection (also see Buss, 2000). This
balance shifts, however, over the course of the woman’s menstrual cycle. As ovulation nears,
fertility increases, and the risks to a man of cuckoldry are at their highest. Therefore, we propose
es, infidelity)
cues to
l logic also
predicts that the interloper bias discussed above may become acute for men when their partners
are most fertile. These predictions are rendered plausible by recent evidence suggesting that men
have adaptations sensitive to their partner’s fertility status. For example, women’s body scent,
al secretions,
rd, & Preti, 1975;
Singh & Bronstad, 1999; Thornhill et al, 2003). Women also report increased love, attraction,
as compared with
2004).
1
time and resources in the offspring of a reproductive competitor. However, the
alarms are also plausibly high. Undue suspicion can damage relationships an
unneeded monitoring of the partner results in missed opportunities to pursue oth
enhancing activities, such as the collection of food or providing care for kin. Th
a bias in men toward over-inferring extra-pair sexual interest (and, in extreme cas
when (a) his partner is nearing midcycle and (b) he is confronted with ambiguous
infidelity (such as his partner’s expressed friendliness to another man). This genera
including scent samples taken from the torso and upper body and samples of vagin
is rated as most attractive during the high fertility phase of the cycle (Doty,
Fo
sexual proprietariness, and jealousy expressed by their partners near ovulation
other cycle phases (Gangestad, Thornhill, & Garver, 2002; Haselton & Gangestad,
1
Note, however, that these studies do not demonstrate bias in men’s inferences of women’s proclivity toward
infidelity. There are at least three possible explanations for this effect: (1) given that women’s extra-pair interests
are elevated at midcycle (Gangestad, Thornhill, & Garver, 2002; Haselton & Gangestad, 2004) men could be
tracking actual risk through their partner’s behavior and adjusting their mate guarding accordingly; (2) women’s
perceptions of their partners behaviors change with their cycle; or (3) men use ovulatory cues to adjust their mate
guarding efforts when their partners are most fertile and hence they are at greatest risk of cuckoldry. The hypothesis
we advance is a version of (3), that men use ovulatory cues to adjust mate guarding and that they become biased
The Paranoid Optimist -- 39
One of the best-researched examples we have discussed is the easily elicited fear of
snakes and spiders. Snakes and spiders were not the only dangerous animals in ancestral
such as
e shaped a
edict that the same
er ancestrally
dangerous animals. Moreover, we hypothesize that the environmental cues that reliably
increased susceptibility to injury should increase false alarm rates in the detection of these
animals and in inferences of their dangerousness. One such cue is ambient darkness (Schaller et
s and states of fear should also amplify other protective biases, including
audi
Krueger and Funder (2004) raised questions about the obsessional focus of many
psychologists on bias and error, which has led to an unnecessarily dreary outlook on human
cognition and a failure to study how accurate judgments are actually made. In the studies we
ually (or often)
d remarkable
unicated (with
al interest and
s studies, partners
tended to agree on whether one partner had forgiven the other (with a maximum correlation of
.44), but they still tended to underestimate how much they had been forgiven (Friesen et al, in
environments. Predatory cats and other large mammals, as well as large reptiles
crocodiles, have likely played a role in the evolutionary history of human, and hav
predator avoidance psychology in humans (Barrett, 1999). Therefore, we pr
effects documented for snakes and spiders will be documented for these oth
al, 2003). Darknes
tory looming (estimating early arrival of objects traveling toward you).
Bias versus Accuracy
have reviewed, our focus on documented biases does not imply that people are us
wildly off-base. In the Haselton and Buss studies (2000), men and women showe
agreement about how much commitment or sexual interest each dating cue comm
correlations above .90). But, at the same time, men overestimated women’s sexu
women underestimated men’s commitment. Likewise, in the forgiveness bia
toward false alarms in their inferences of their partner’s extra-pair sexual interest and behavior. Controlled
laboratory experiments may be required to test the infidelity-bias hypothesis.
The Paranoid Optimist -- 40
press). Thus, as Fletcher (2002) noted, bias and accuracy can vary quite independently, and
systematic bias does not preclude reasonable accuracy.
cy. An error
Accuracy, or judgmental
ness
dominance or
sociosexual orientation of others (Gangestad, Simpson, DiGeronimo, & Biek, 1992). If the
fitness consequences of discrimination are large, and there is a differential cost of errors in one
direction or the other, then a judgmental system should be both sensitive and biased. In
are greater indicators of sexual interest than
. stoking one’s date on the thigh), but it also pays to overestimate the degree to
whi
The Rational Actor?
An important reason for seeking an explanatory framework for biases concerns the
adequacy of human reasoning. Much social theory, particularly in economics and political
le to use information
ut not to be
vationally
ts, and
experimental economists, has often cast doubt on the accuracy of the rational actor assumption
(Bell, 1995; Davis & Holt, 1993; Kahneman et al., 1982). However, if observed departures from
rationality are studied piecemeal and accepted as so many quirks of human beings without
seeking deeper explanation, social science becomes balkanized between theorists who have a
The criteria for predicting bias are different from those for predicting accura
management bias is predicted when errors differ reliably in their costs.
sensitivity, is predicted when valid cues are available (Funder, 1995) and the fit
consequences of correct discrimination are large—for example, in judging the
courtship, it is important to recognize that some cues
others (smiling vs
ch cues indicate interest if it helps a man to avoid a miss.
science, depends on conceptualizing the individual as a rational actor ab
available to him in an optimal way given his aims and objectives. If people turn o
rational in the required sense, such models lack validity. Experimentally and obser
based research, such as that carried out by social psychologists, anthropologis
The Paranoid Optimist -- 41
powerful explanatory framework that lacks validity, and empiricists who have an accurate list of
phenomena but no explanations (Hermann-Pillath, 1994; Nettle, 1997). Moreover, the outlook
ly that people, because of limitations
in co
defects suggests
oretically
and explained by optimality when viewed through the long lens of evolutionary theory. Thus, the
human mind shows good design, though it is design for fitness-maximization, not truth
preservation. This reorientation accords with other recent work in psychology. For example, the
up of simple
ces, are simply
e of ‘cognitive
illusions’ or pervasive departures from optimality. More recent work, however, has questioned
this bleak view. Some cognitive illusions disappear or greatly attenuate when the task is
presented in an ecologically valid format (Cosmides & Tooby, 1996; Gigerenzer & Hoffrage,
199 y, may in effect
med recurrently
just as well as
complex normative models under real-world conditions of partial knowledge (Gigerenzer &
Todd, 1999). There are even circumstances in which they perform better than normative models,
the so-called ‘less is more’ effect. The less is more effect occurs because simple heuristics can
exploit structural features of the decision-making environments which are noisy and uncertain
for human rationality is bleak, since the implication is simp
gnitive machinery, are not capable of optimal decision making.
The reinterpretation of many biases as design features rather than design
a different perspective. Both the content and direction of biases can be predicted the
heuristics and biases tradition (Kahneman et al., 1982) saw the mind as made
problem solving tools that, while functional over a restricted range of circumstan
inadequate to produce optimal judgment in general, resulting in a wide rang
5). Ecological validity, a long-standing but under-theorized term in psycholog
be equated to the task format approximating some task that humans have perfor
over evolutionary time.
Moreover, many of the simple heuristics that people actually use perform
The Paranoid Optimist -- 42
and contain multiple cues. EMT complements the ‘less is more’ principle with a ‘biased is better’
principle; under some circumstances, which can be predicted in a principled way, biased
strategies are actually superior to non-biased ones.
g strategies can be
is
uncertainty about likelihoods, a biased reasoning strategy can actually do better than an unbiased
one. It strikes us that these conditions are likely to characterize many of the real dilemmas that
have faced us and our ancestors. Since dilemmas are never repeated with exactly the same
r various kinds
of o positive or
hould evolve.
Error management theory is an additional element in a picture of the mind as a well-
designed instrument for solving the kinds of problems that have faced human beings over their
evolutionary history. Many apparent quirks of human thought, from our fear of harmless spiders,
to our superstition and paranoia, to our eternal optimism, may be optimal adaptations to the
worlds in which we have lived.
Conclusion
EMT predicts that over a certain set of conditions, biased reasonin
adaptive. Most importantly, where error costs are known and asymmetric, and there
parameters, likelihoods are very hard to infer accurately. However, the payoffs fo
utcomes, from being bitten by a snake to obtaining a mate, are recurrently
negative over evolutionary time. Thus, EMT predicts that highly specific biases s
The Paranoid Optimist -- 43
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Table 1: Protective Biases in Perception, Attention, and Learning
Domain False Positive (FP) Cost of FP False Negative (FN) Result Cost of FN
Approaching sounds o early Low y sou H Auditory Looming:
wards
underestimating time to
ival
Ready to Struck b rce igh
Bias to
arr
Dangerous an
(e.g.,
imals
snakes and
armless snakes
and spiders
Low fear venomous
snakes and spiders
H elicited fear
reaction to snakes and
spiders
spiders)
Fear h Fail to igh Easily
Dangerous persons Fear harmless people w,
on the relationship
Fail to fear truly hostile
others
elicited fear
and/or inferences of
ousness
May be lo depending High Easily
danger
Food aversions Avoid a food that is
s
Non-zero but not too Eat a fatally toxic food H Avoidance of any food
at may be associated
sickness
usually harmles high
igh
th
with
Diseased persons Avoid a person who is
not infectious
May be low, depending
on the relationship
Become infected Tendency to avoid
persons with physical
afflictions
Often high
The Paranoid Optimist -- 58
Table 2: Biases in Social and Self Perception
in sitive t of FP e negative Cost of FN Result Doma False po Cos Fals
Unexplained changes
environm
i
ent
human
agency
agai
th
ist—low
t co
stile group
dividual
r displ
mpetition or
ility—
macy; agency bias
n Assume Vigilance
conspecific
nst a
at does
Fail to detec
or ho
not ex
in
mpeting
or
Suffe
co
acement
Illusion of ani
host high
Sinister attribu
respon
tion or
se to social
gative
ion where
e
ial
works—co
detect
enuine negativ
s
ns
marginal
twork
ognition in situations
inality or low status;
veness bias
scrutiny
Assume ne
evaluat
Impairs soc
net
there is non
uld be
Fail to
g
significant
e
High if i
evaluation
ecure or
within social
Paranoid c
of marg
ne
negative forgi
Dispositional Inference v
enduring disposi
ortuni
ang
signi
manipulative dispositions
High for ce
negative tr
al attribution error for
uncertain, negative traits (e.g.,
)
Assume negati e,
tion
Lost opp
social exch
ty for
e–
Fail to detect
could be ficant
in others
harmful,
rtain
aits
Fundament
social cheating
Cooperation with othe e can
r cheat
without negative
ces
ecia
when costs of
ostracism are
ne s
even
safely defect
(e.g., w
ection by ot
—espe
esource amount given
is small (e.g., small
amo
Social exchange bias: tendency to
cooperate when defection has
greater payoff
rs Believe on
defect o
consequen
High—esp lly
great
Infer that o
cooperate
one could
hould
though
Low
r
or cheat
det
ithout
hers)
dollar
cially when
unt)
Men’s perception of
terest
Inferring interest Wasted courtship
elatively
low
Inferring no interest
Missed reproductive
pportun
Overperception of women’s
terest by men
women’s sexual in where there is none effort—r
when there is o ity—high sexual in
Women’s perception o
ent
g willingness
ere
ere is none
Desertion—hi Inferring unwil
her
willingness
Delayed start to
io
relatively low
Underperception of men’s
commitment by women
f Inferrin
men’s commitm to commit wh
th
gh lingness
to commit w e there is
reproduct
n—
Beliefs in personal
control and efficacy
Assuming control or
efficacy where there
is none
Low as long as the
costs of trying and
failing are low
Assuming inability to
control where control is
possible
Passivity and
opportunity costs—high
Positive illusions, illusion of
control
The Paranoid Optimist -- 59
Figure 1. The optimum threshold (likelihood ratio) for adopting a belief S where the cost of the
bability of s set at
0.1. A threshold less than 1 represents a bias towards adopting S. For explanations see text.
false positive is fixed at 1 and the cost of the false negative varies, with the pro
0
1
2
3
4
5
0 5 10 15 20 25 30 35 40 45 50
Cost of false negative
Optimum threshold
The Paranoid Optimist -- 60
Figure 2. The optimum threshold (likelihood ratio) for adopting a belief S where the cost of the
ability of s set at
0.6. A threshold greater than 1 represents a bias against adopting S. For explanations see text.
false negative is fixed at 5 and the cost of the false positive varies, with the prob
0
2
4
6
8
10
0 5 10 15 20 25 30 35 40 45 50
Cost of false positive
Optimum threshold
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This chapter considers the relationship between emotions and deliberative rationality. It argues that there are evolutionary reasons to think that emotions are in some cases likely systematically to skew rationality. Standard models of rationality assume that the mind is able to come to accurate assessments of the probability of future contingencies. However, robust evidence shows that people systematically overestimate the probability of positive future contingencies, and underestimate the probability of negative ones - only those who are depressed or dysphoric come to accurate assessments. The chapter argues that there are good evolutionary reasons why this should be the case, since there is an asymmetric pattern of costs and benefits from getting motivational judgements wrong.
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In two experiments, observers received information about a stimulus person and then attributed a given level of morality to that person. Attributions of morality based on the stimulus person's immoral (as opposed to moral) behavior were relatively unaffected by situational demands surrounding the behavior. That is, a person who stole or committed adultery was judged to be relatively immoral, regardless of situational pressures that appeared to facilitate the behavior. Varying the type of situational demand (reward vs. cost) did not alter this basic effect. Unlike morality attributions, causal attributions based on moral and immoral behavior were affected by situational demands to an equal extent. The results also indicated that impressions of morality formed in one context readily generalized to other aspects of morality. For example, a person who committed adultery was thought to be more likely to lie and steal than one who was not adulterous. It is well known that negative information weighs heavily in one's overall impression of a person (Kanouse & Hanson, 1972). For example, a single immoral behavior (such as stealing) is often enough to sour one's evaluation of a person. Further, this negative evaluation tends to persist even when the person is simultaneously credited with several very