Behavioral Immune Trade-Offs: Interpersonal Value Relaxes Social Pathogen Avoidance

Abstract

Behavioral-immune-system research has illuminated how people detect and avoid signs of infectious disease. But how do we regulate exposure to pathogens that produce no symptoms in their hosts? This research tested the proposition that estimates of interpersonal value are used for this task. The results of three studies (N = 1,694), each conducted using U.S. samples, are consistent with this proposition: People are less averse to engaging in infection-risky acts not only with friends relative to foes but also with honest and agreeable strangers relative to dishonest and disagreeable ones. Further, a continuous measure of how much a person values a target covaries with comfort with infection-risky acts with that target, even within relationship categories. Findings indicate that social prophylactic motivations arise not only from cues to infectiousness but also from interpersonal value. Consequently, pathogen transmission within social networks might be exacerbated by relaxed contamination aversions with highly valued social partners.

Full text

https://doi.org/10.1177/0956797620960011
Psychological Science
2020, Vol. 31(10) 1211 –1221
© The Author(s) 2020
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DOI: 10.1177/0956797620960011
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ASSOCIATION FOR
PSYCHOLOGICAL SCIENCE
Research Article
Everyday life involves navigating a minefield of infec-
tious microbes that aim to exploit our bodies for their
own gain. We deftly avoid most of these pathogens, as
if we have some awareness of where they lie, despite
their invisibility to the naked eye. Such avoidance is
often affectively motivated. For example, the scents of
bodily wastes—reliable sources of pathogens through-
out our evolutionary history—elicit disgust, which moti-
vates contact avoidance (Tybur, Lieberman, Kurzban,
& DeScioli, 2013). Similar avoidance occurs socially;
people shun those unlucky enough to display many
infectious disease symptoms, including the pustules
caused by smallpox, the asymmetric swellings caused
by mumps, and the fluid-filled lesions caused by yaws
(Oaten, Stevenson, & Case, 2011). Understanding
responses to these and other cues to pathogens has
formed the bedrock of behavioral-immune-system
research (Ackerman, Hill, & Murray, 2018; Murray &
Schaller, 2016; Neuberg, Kenrick, & Schaller, 2011).
Yet a behavioral immune system that motivates
avoidance of only individuals covered in rashes, pox,
or swellings would leave us exposed to myriad patho-
gens transmitted by individuals showing no signs of
illness. Consider the consequences of contact with the
early 20th century cook Mary Mallon (“Typhoid Mary”),
who transmitted sometimes-lethal typhoid infections to
dozens of people despite showing no symptoms of illness
herself. Similar asymptomatic transmission is common
960011PSSXXX10.1177/0956797620960011Tybur et al.Interpersonal Value and Pathogen Avoidance
research-article2020
Corresponding Author:
Joshua M. Tybur, Vrije Universiteit Amsterdam, Department of
Experimental and Applied Psychology, Van der Boechorststraat 7,
Room MF-C570, 1081 BT Amsterdam, The Netherlands
E-mail: j.m.tybur@vu.nl
Behavioral Immune Trade-Offs:
Interpersonal Value Relaxes
Social Pathogen Avoidance
Joshua M. Tybur1,2 , Debra Lieberman3, Lei Fan1,2 ,
Tom R. Kupfer1, and Reinout E. de Vries1,2
1Department of Experimental and Applied Psychology, Vrije Universiteit Amsterdam; 2Institute of Brain and
Behavior Amsterdam; and 3Department of Psychology, University of Miami
Abstract
Behavioral-immune-system research has illuminated how people detect and avoid signs of infectious disease. But how
do we regulate exposure to pathogens that produce no symptoms in their hosts? This research tested the proposition
that estimates of interpersonal value are used for this task. The results of three studies (N = 1,694), each conducted
using U.S. samples, are consistent with this proposition: People are less averse to engaging in infection-risky acts not
only with friends relative to foes but also with honest and agreeable strangers relative to dishonest and disagreeable
ones. Further, a continuous measure of how much a person values a target covaries with comfort with infection-risky
acts with that target, even within relationship categories. Findings indicate that social prophylactic motivations arise not
only from cues to infectiousness but also from interpersonal value. Consequently, pathogen transmission within social
networks might be exacerbated by relaxed contamination aversions with highly valued social partners.
Keywords
infectious disease, behavioral immune system, disgust, evolutionary psychology, welfare trade-offs, open data, open
materials, preregistered
Received 3/24/20; Revision accepted 8/24/20

1212 Tybur et al.
across infectious agents. For example, volunteer infec-
tion studies indicate that 90% of participants dosed with
influenza shed viral particles, but only 70% show symp-
toms (Carrat etal., 2008). Among people who do even-
tually become ill, viral shedding begins before symptoms
appear and peaks before illness does. Asymptomatic
transmission is typical of many sexually transmitted
infections (Farley, Cohen, & Elkins, 2003), and it appears
to underlie much of the spread of the SARS-CoV-2 virus
that causes COVID-19 (Li etal., 2020). Further, a person
can transmit pathogens without being infected, simply
by touching a pathogen-contaminated surface. Ulti-
mately, every person can transmit pathogens, and
apparent health tells little about many common infec-
tion threats.
How do people navigate a social world in which
infectious agents are ubiquitous yet often undetectable,
even to a behavioral immune system that seems tailored
to detecting and neutralizing pathogens?
Trade-Offs: The Costs and Benefits
ofMitigating Exposure to Pathogens
As highlighted in the behavioral-immune-system litera-
ture, investments in pathogen avoidance often impose
costs on other fitness-promoting behaviors (e.g., Oaten,
Stevenson, & Case, 2009; Schaller, 2015; Tybur & Lieberman,
2016). Consider the most severe and most relaxed pathogen-
avoidance strategies possible. On one extreme, we could
experience motivations to avoid all direct and indirect
contact with all people. While minimizing exposure to
pathogens, such motivations would largely eliminate
food sharing, sexual behavior, cooperation on joint
tasks, and aid to kin and romantic partners (e.g., Case,
Repacholi, & Stevenson, 2006; Fleischman, Hamilton,
Fessler, & Meston, 2015). On the other extreme, we
could experience no motivations to avoid direct and
indirect contact—we could feel comfortable touching
or licking any person or any object touched by another
person. This approach, while eliminating the social
costs of contact avoidance, would leave us severely
vulnerable to infection. A well-designed behavioral
immune system should instead balance the costs of
pathogen exposure against those of social avoidance in
a target-specific manner. Guided by the considerations
described above, researchers have uncovered evidence
that mandrills groom parasitized maternal kin but avoid
grooming other parasitized conspecifics (Poirotte &
Charpentier, 2020) and that human mothers report less
disgust toward their own baby’s diapers than other
babies’ diapers (Case etal., 2006).
More broadly, disgust “source effects” are consistent
with the idea that similar trade-offs operate outside the
kinship domain; for example, some studies have found
that people imagine the bodily fluids or wastes from a
friend to be less aversive than those from a stranger
(Curtis, Aunger, & Rabie, 2004; Peng, Chang, & Zhou,
2013; Rozin, Nemeroff, Wane, & Sherrod, 1989; Stevenson
& Repacholi, 2005). Rather than reflecting lower path-
ogen avoidance toward more valued conspecifics,
though, these findings have been interpreted as sug-
gesting that familiarity is treated as information regard-
ing infection threat, just as pustules and lesions are. In
the current study, we tested the alternative account
described above: that willingness to engage in infection-
risky behaviors tracks interpersonal value, even in the
absence of illness symptoms.
Interpersonal Value Between
andWithin Categories
Interpersonal value does not map neatly onto catego-
ries labeled with terms such as family, friend, and foe.
The category “kin” alone reflects multiple relationship
types (e.g., parent, offspring, sibling, half-sibling), and
relationships are differentially valued within such cat-
egories (e.g., siblings; Sznycer, De Smet, Billingsley, &
Lieberman, 2016). Strangers also vary in interpersonal
affordances: Some are more likely to become valuable
exchange partners, and others are more likely to inflict
social costs. Hence, if social pathogen avoidance tracks
Statement of Relevance
People deftly navigate around pathogens, including
those hiding in bodily wastes, spoiled foods, and
individuals with infectious disease symptoms, even
without consciously considering the consequences
of infection. They do so because natural selection
has shaped our sensory and motivational systems
as a kind of behavioral immune system. However,
many pathogen threats, including those posed by
asymptomatic influenza and COVID-19 carriers,
show no signs of infectiousness. The current work
uncovers new information regarding how people
navigate these types of infection threats. Results
from three studies indicate that people feel strongly
motivated to avoid infection-risky behaviors with
unsavory strangers and disliked acquaintances, but
they are more comfortable taking identical risks
with individuals whose welfare they value. These
findings may help explain epidemiological patterns
such as family-group clustering: Infections spread
not only because of proximity but also because
of greater comfort with exposure to the unseen
pathogens transmitted by people we value.

Interpersonal Value and Pathogen Avoidance 1213
perceptions of interpersonal value, then people should
be more comfortable with infection-risky behaviors not
only with individuals from less valued categories but
also with more interpersonally valued targets within
categories.
Although interpersonal value is strongly influenced
by kinship, it is also shaped by, among other things,
mutual valuation, as occurs in friendships, and inclina-
tions to engage in reciprocity, as occurs in exchange
partners (Tooby & Cosmides, 1996). These disparate
sources of benefits are putatively integrated into a
welfare-trade-off ratio (WTR)—an individual’s willing-
ness to trade off his or her welfare for that of another
(Delton & Robertson, 2016; Kirkpatrick, Delton,
Robertson, & de Wit, 2015; Smith, Pedersen, Forster,
McCullough, & Lieberman, 2017; Tooby, Cosmides, Sell,
Lieberman, & Sznycer, 2008). We used tasks that mea-
sure willingness to trade-off one’s own welfare for that
of another to investigate whether comfort with poten-
tially infectious contact tracks interpersonal value.
Overview of the Present Studies
Across three studies, we tested the hypothesis that moti-
vations to avoid infection-risky behaviors relate to
target-specific interpersonal value. In Studies 1 and 2,
participants reported their comfort with infection-risky
acts with a target they know personally (either a roman-
tic partner, a friend, an acquaintance, or a disliked
other), and they completed a target-specific WTR task.
In Study 3, participants reported their comfort with
these same infection-risky acts with a stranger, who
was described as either high or low on honesty-humility
and agreeableness, two personality traits that should
inform expected interpersonal value. Participants from
each study were U.S. residents recruited using Amazon’s
Mechanical Turk. Samples drawn from this pool are
similar to nationally representative samples in many
ways, though they tend to be a bit younger, less reli-
gious, and less politically conservative (Levay, Freese,
& Druckman, 2016). Preregistrations, data, and R analy-
sis scripts for all three studies are available on OSF
(https://osf.io/4agk8/).
Study 1
Method
Study 1 examined whether people are less avoidant of
potentially infectious contact with individuals from
more valuable relationship categories and whether
interpersonal value predicts pathogen avoidance within
categories.
Participants. We preregistered a target of 500 partici-
pants. We did not use an a priori effect-size estimate,
though this sample afforded 80% power to detect a small
effect size (r) of .12. Five hundred four individuals
(55.16% male; age: M = 35.88 years, SD = 10.2) partici-
pated in exchange for $1.50. All respondents provided
informed consent.
Procedure. After reporting demographic information
(e.g., sex, age, relationship status, income), each partici-
pant was randomly assigned to think of either (a) their
romantic partner, (b) their closest friend, (c) an acquain-
tance, or (d) someone they know personally but dislike.
Participants who had previously reported being in a
romantic relationship had a 40% chance of being assigned
to the romantic-partner condition and a 20% chance of
being assigned to each of the other three conditions; sin-
gle participants had a 33% chance of being assigned to
the three non-romantic-partner conditions. Participants
were first asked to write the target’s initials, which
appeared in the remaining questions about the target.
They were then asked to write a few sentences describ-
ing the target’s physical appearance, to report how long
they have known the target, and to report the target’s age
and sex.
To measure motivations to avoid pathogen exposure,
we generated 10 items inspired by the germ-aversion
subscale from the Perceived Vulnerability to Disease
scale (Duncan, Schaller, & Park, 2009). Example items
included “Using [target]’s deodorant stick on yourself,”
“Wearing a hat that [target] has worn many times,” and
“Touching a handkerchief that [target] used to blow his
or her nose.” Participants rated each item on a scale
from −3 (very uncomfortable) to 3 (very comfortable),
with the midpoint labeled 0 (neutral). A principal-axis
factor analysis suggested that these items varied along
a single dimension (all factor loadings were above 0.74;
α = .96). Mean contact comfort was 0.06 (SD = 1.97).
Lower scores were interpreted as corresponding with
greater motivations to avoid exposure to the pathogens
potentially transmitted by the target.
To assess interpersonal value, we used a WTR task
(Delton & Robertson, 2016; Kirkpatrick etal., 2015;
Smith etal., 2017). In this task, participants are asked
to select one of two options, the first of which involves
the participant receiving money, and the second of
which involves the target receiving money. Each target-
benefiting decision is characterized by a different wel-
fare trade-off—that is, a different ratio of benefits
received by the target relative to what could have been
received by the participant. For example, for one of the
items, participants decided whether they would rather
receive $17 with the target receiving nothing or receive

1214 Tybur et al.
nothing with the target receiving $37. Choosing the
beneficial option for the target would imply a WTR
toward that target of at least 0.45 (i.e., 17/37). Partici-
pants completed the same 60 items described by
Kirkpatrick et al. (2015), which include six anchor
points (fixed values received by the target), each of
which has 10 values that the participant would receive.
Switch points—the ratio at which participants begin
choosing the benefit for the target—were calculated for
each anchor and averaged (α = .99). Further details are
provided in the Supplemental Material available online.
We also asked participants to rate the target’s honesty-
humility (for an overview, see de Vries, Tybur, Pollet,
& van Vugt, 2016) using the 10 honesty-humility items
from the HEXACO-60 (Ashton & Lee, 2009; α = .88).
Individuals higher in honesty-humility report less will-
ingness to exploit others (Van Gelder & de Vries, 2012),
and they behave more prosocially in tasks with financial
consequences (e.g., returning more money in trust
games, offering more money in dictator games;
Thielmann, Spadaro, & Balliet, 2020). In sum, partners
higher in honesty-humility are more likely to confer
benefits in social relationships and hence should be
more valued as relationship partners.
Finally, we also measured the extent to which par-
ticipants felt generally motivated to avoid pathogen
cues using the seven-item pathogen domain of the
Three Domain Disgust Scale (Tybur, Lieberman, &
Griskevicius, 2009), which asks participants to rate
seven items (e.g., “Stepping in dog poop”) on a scale
from 0 (not at all disgusting) to 6 (extremely disgusting;
α = .83).
Data exclusion. We excluded participants with more
than two switch points within any of the six WTR anchors
(n = 35), three participants whose descriptions of their
partners were nonsensical or demonstrated poor English,
and two participants who selected a gender option indi-
cating that they were neither a man nor a woman. These
latter participants were excluded so that sex differences
could be examined. Results reported below are based on
the remaining 464 participants. All outcomes of null-
hypothesis significance testing (i.e., p < .05) remained
when no exclusions were made.
Results
Participants were more comfortable with potentially
infectious contact with targets whose welfare they val-
ued, r = .68, 95% confidence interval (CI) = [.63, .73],
p < .001 (see Fig. 2), and with targets rated as higher
on honesty-humility, r = .47, 95% CI = [.40, .54], p <
.001. A number of other variables also related to contact
comfort, including sensitivity to pathogen disgust, r =
−.22, 95% CI = [−.30, −.13], p < .001, and target sex, with
participants reporting greater comfort with infectious
contact with women than with men, r = .17, 95% CI =
[.08, .26], p < .001. Notably, the main effect of target sex
was qualified by an interaction with participant sex1
(details are provided in the Supplemental Material).
Critically, contact comfort also varied across relation-
ship type (romantic partner, close friend, acquaintance,
enemy), F(3, 460) = 213.52, p < .001, η2 = .58, 90%
CI = [.54, .62] (see Fig. 1), as did WTR and honesty-
humility (for target-category differences in WTR and
honesty-humility and a full correlation matrix, see the
Supplemental Material).
We next conducted hierarchical regression analyses
to test whether WTR value relates to contact comfort
independently of relationship type. In a first step
(adjusted R2 = .08; see Fig. 2), contact comfort was
regressed on variables unrelated to WTR, including par-
ticipant sex and income, target sex, and pathogen-
disgust sensitivity. Adding WTR, b = 2.36, p < .001,
rp2 = .33, 90% CI = [.27, .39], and target honesty-humility,
b = 0.19, p = .03, rp2 = .03, 90% CI = [.005, .06], to the
model accounted for an additional 42.82% of the vari-
ance in contact comfort. But were these effects of WTR
entirely accounted for by the category of partner that
participants were asked to imagine? No. Although the
third step incorporating three orthogonally coded vari-
ables representing the four relationship categories
accounted for an additional 13.43% of variance in con-
tact comfort, WTR continued to account for unique
variance, b = 0.85, p < .001, rp2 = .05, 90% CI = [.01, .08],
though target honesty-humility did not, b = 0.05, p =
.49, rp2 < .001, 90% CI = [−.01, .01].
Study 2
Method
Study 2 closely mirrored Study 1, with four exceptions.
First, given that WTR, rather than target-rated honesty-
humility, uniquely related to contact comfort, we did
not assess target honesty-humility. We instead assessed
participants’ prosocial personality traits, which might
jointly relate to WTR and pathogen avoidance (Kirkpatrick
etal., 2015; Kupfer & Tybur, 2017). Second, given asym-
metries in target sex across the four categories used in
Study 1 (4%, 70%, 76%, and 74% same-sex for romantic
partner, closest friend, acquaintance, and disliked other,
respectively), we randomly assigned each participant
to picture either a male or a female target. To accom-
modate this change, we eliminated the romantic-partner
condition.

Interpersonal Value and Pathogen Avoidance 1215
Participants. We preregistered a recruitment target of
430 individuals, which we anticipated would be reduced
to approximately 387 after exclusions. This sample size
was targeted to facilitate exploratory analyses involving
participant sex and target sex (see the Supplemental
Material), and it provided more than 99% power to detect
the relation between WTR and contact comfort observed
in Study 1. We recruited only participants not enrolled in
Study 1. Four hundred thirty individuals (56.28% male;
age: M = 36.29 years, SD = 10.99) participated in exchange
for $2.00. All respondents provided informed consent.
Procedures. Procedures were identical to those in
Study 1, with a few notable exceptions. First, each partici-
pant was randomly assigned to picture either a man or a
woman from one of the three categories (i.e., closest
male friend, closest female friend, male acquaintance,
female acquaintance, male disliked other, or female dis-
liked other). Second, they provided self-reports of agree-
ableness (α = .84) and honesty-humility (α = .81; rather than
target ratings of honesty-humility) from the HEXACO-60
(Ashton & Lee, 2009). Third, given high consistency across
the six anchor points used in Study 1, they completed a
30-item WTR measure rather than the 60-item version (α =
.97). They also completed a handful of additional items,
which were not included in our preregistered analysis plan
(see the Supplemental Material).
Data exclusion. We excluded 19 participants with
more than two switch points within any of the three WTR
anchors, seven participants whose descriptions of their
partners were nonsensical or demonstrated poor English,
and one participant who described their gender identity
as neither male nor female. The results reported below
are based on the remaining 403 participants. All out-
comes of null-hypothesis significance testing (i.e., p <
.05) remained when no exclusions were made.
Results
As in Study 1, participants were more comfortable with
potentially infectious contact with more interpersonally
valued targets, r = .61, 95% CI = [.54, .67], p < .001 (see
Fig. 2). Contact comfort also related to pathogen-disgust
sensitivity, r = −.24, 95% CI = [−.33, −.15], p < .001. And,
as expected, it also varied across relationship type
(close friend, acquaintance, enemy), F(2, 397) = 116.7,
p < .001, η2 = .37, 90% CI = [.31, .42] (see Fig. 1). A full
list of correlations is provided in the Supplemental
Material.
We next ran our preregistered analyses, in which we
first entered participant characteristics (sex, age, self-
reports of honesty-humility, agreeableness—as opposed
to target reports used in Study 1—and pathogen-disgust
sensitivity), then target characteristics (sex, age, WTR)
Study 1
−3
−2
−1
0
1
2
3
Contact Comfort
Study 2 Study 3
Romantic
Partner
Friend Acquaintance Enemy Friend Acquaintance Enemy High-Value
Stranger
Low-Value
Stranger
Fig. 1. Mean comfort with infection-risky contact with each target type, separately for Studies 1 through 3. In each violin plot, the horizontal
line indicates the median, the white box indicates the interquartile range of the data, the shaded area indicates the density of the data, and
the whiskers extend 1.5 times the interquartile range. Outliers are indicated by dots.

1216 Tybur et al.
Target
Study 1
Romantic Partner
Friend
Acquaintance
Enemy
Study 3
High-Value Stranger
Low-Value Stranger
−3
−2
−1
0
1
2
3
−3
−2
−1
0
1
2
3
−0.45 0.05 0.55 1.05 1.55
WTR
−0.45 0.05 0.55 1.05 1.55
WTR
Study 1
Contact Comfort
Contact Comfort
−3
−2
−1
0
1
2
3
Contact Comfort
Study 2
Study 3
−0.45 0.05 0.55 1.05 1.55
WTR
Friend
Acquaintance
Enemy
Study 2
Fig. 2. Relations between welfare-trade-off ratio (WTR) and comfort with infection-risky contact, separately for each target type in
Studies 1 through 3. In each scatterplot, the solid line indicates the best-fitting relationship between WTR and contact comfort across
categories, and the dashed lines indicate the best-fitting relationship within each target category. Shaded areas around the regression
lines indicate 95% confidence intervals.
in a second step, then relationship category in a third
step. Participant characteristics accounted for approx-
imately 6.16% of the variance in contact comfort, and
target characteristics apart from relationship category
accounted for an additional 36.82% of the variance.
In that second step, WTR was most strongly related
to contact comfort, b = 2.06, p < .001, rp2 = .36, 90%
CI = [.29, .42]. Adding relationship category accounted
for an additional 7.77% of the variance in contact
comfort, but, as in Study 1, the unique effect of WTR
remained, b = 1.13, p < .001, rp2 = .09, 90% CI = [.05,
.14].

Interpersonal Value and Pathogen Avoidance 1217
Study 3
Method
Study 3 was designed to address limitations of Studies
1 and 2: Each participant pictured a different target,
and unmeasured third variables could have confounded
pathogen-avoidance motivations and interpersonal
value. For example, given that people with many symp-
toms of illness are socially devalued (Oaten et al.,
2011), less interpersonally valued partners might actu-
ally be more infectious, and the relation between WTR
and pathogen-avoidance motivations could have
reflected stronger avoidance of more infectious indi-
viduals. To address this limitation, we accounted for
the identity of the target in Study 3. Participants saw a
picture of a stranger and read a description containing
information about that person’s value as an exchange
partner. Given that individuals higher in honesty-
humility and agreeableness behave more prosocially in
social dilemmas (e.g., dictator games, trust games, ulti-
matum games; Thielmann, Spadaro, & Balliet, 2020),
and such games serve as abstractions of valuable
behavior in exchange relationships (e.g., willingness to
share resources, trust, forgiveness; Murnighan & Wang,
2016), we designed the descriptions to communicate
either high honesty-humility and agreeableness or low
honesty-humility and agreeableness. Similar types of
information about strangers have been shown to influ-
ence the magnitude of WTRs in the expected direction
(e.g., Smith etal., 2017). We predicted that motivations
to avoid pathogens would be higher for targets low in
honesty-humility and agreeableness, because these tar-
gets offer little benefits that might offset potential costs
of infection, and that target-specific WTR would again
relate to willingness to expose oneself to unseen patho-
gens. Notably, all targets were strangers to participants,
and any differences in contact comfort across high ver-
sus low agreeableness and honesty-humility targets
cannot be explained by putatively greater infection
threats posted by strangers relative to friends (e.g., Peng
etal., 2013).
Participants. We preregistered a recruitment target of
870 individuals, which we anticipated would be reduced
to approximately 800 after exclusions. This sample size
afforded 80% power assuming a small effect of the manip-
ulation (d = 0.20), with a target intercept variance compo-
nent of .15 and a target slope variance of .02 (Westfall
etal., 2014). Nine hundred five individuals (49.94% male;
age: M = 38.22 years, SD = 11.64) participated in exchange
for $1.60. All respondents provided informed consent.
Procedures. Each participant was randomly assigned to
see and read about a target that was described as either
high or low in honesty-humility and agreeableness. We
employed a stimulus-sampling approach to target appear-
ance, which allows for inferences across populations of
stimuli as well as populations of participants (Westfall
etal., 2014). Each participant was also randomly assigned
to see one of 40 different faces (20 male, 20 female)
selected from the Chicago Face Database (Ma, Correll, &
Wittenbrink, 2015). Given arguments that physical attrac-
tiveness is treated as indicative of infection risk (Park, van
Leeuwen, & Stephen, 2012), we aimed to sample from a
range of attractiveness levels. We identified the man rated
most attractive in the normed data set (a rating of 5 on a
1- to 7-point scale based on data reported by Ma et al.)
and selected him and 19 other men, each with an attrac-
tiveness rating 0.15 scale units below the previous face.
We then selected female targets that matched the male
targets on attractiveness ratings.
In both conditions, participants read a description
of the target. This description was based on items from
each of the four facets of honesty-humility (sincerity,
fairness, greed avoidance, and modesty) and each of
the four facets of agreeableness (forgiveness, gentle-
ness, flexibility, patience). Low-value targets were
described on the low end of each facet, and high-value
targets were described on the high end of each facet
(for complete descriptions, see the Supplemental Mate-
rial). After seeing the target and reading the description,
participants completed the same contact-comfort items
used in Studies 1 and 2 (α = .91) and the same 30-item,
three-anchor WTR measure used in Study 2 (α = .97).
They also rated the target’s honesty and kindness (on
11-point scales) as well as other characteristics (for a
complete list, see the Supplemental Material). As
intended, relative to targets high in prosocial personal-
ity traits, targets low in prosocial personality traits were
rated less honest (M = 9.53 vs. M = 2.39, p < .001) and
less kind (M = 9.33 vs. M = 2.93, p < .001). Further
details are provided in the Supplemental Material.
Data exclusion. We excluded 40 participants whose
des criptions of the target were nonsensical or demonstrated
poor English, eight participants who described their gender
identity as neither male nor female, and 30 participants
with more than two switch points within any of the three
WTR anchors. Results reported below are based on the
remaining 827 participants. All outcomes of null-hypothesis
significance testing (i.e., p < .05) remained when no
exclusions were made.
Results
Using a random-effects model, we regressed contact
comfort on target condition (high value vs. low value)
and initially modeled random intercepts for stimuli and

1218 Tybur et al.
random slopes for the effect of interpersonal value
across stimuli. We removed random slopes that pre-
vented model convergence. People were more comfort-
able with exposure to pathogens when the targets were
described as high in prosocial personality traits (M =
−0.93, 95% CI = [−1.04, −0.81]) than when they were
described as low in prosocial personality traits (M =
−1.8, 95% CI = [−1.89, −1.70], F(1, 822) = 126.1, p < .001.
When WTR was added as a predictor, both WTR and
the manipulation were related to comfort with exposure
to pathogens (both ps < .001; see Fig. 2). The effect of
the manipulation and WTR remained when we further
controlled for participant pathogen-disgust sensitivity,
participant sex, and target sex, ps < .001. Full details
are provided in the Supplemental Material.
Discussion
Results from each of three studies revealed that motiva-
tions to avoid infection-risky contact varied markedly
across targets with no clear symptoms of illness. Much
of this variation was accounted for by targets’ interper-
sonal value to perceivers. Participants were less averse
to infection-risky contact with targets from categories
that are, on average, more highly valued (e.g., close
friends vs. disliked others), and they were less averse
to infection-risky contact with agreeable and honest
strangers than with disagreeable and dishonest ones.
Further, even within target categories, comfort with
infection-risky contact related to a continuous measure
of interpersonal value—for example, people who valued
their closest friend more were also less averse to infec-
tion-risky contact with that friend. We discuss how these
findings can inform both the burgeoning behavioral-
immune-system literature and our understanding of
how infectious disease spreads.
Implications for understanding the
behavioral immune system
The behavioral-immune-system literature largely focuses
on understanding how people detect and respond to
features that putatively provide information regarding
infectiousness, such as pustules and swellings (Ackerman
etal., 2018; Murray & Schaller, 2016; Neuberg etal.,
2011; Oaten etal., 2011). The current study is a step
forward in understanding pathogen avoidance even in
the absence of such cues, and it raises critical issues
for future research.
First, growing evidence suggests that the behavioral
immune system does not output the same pathogen-
avoidance motivations across all contexts. It is instead
flexible, weighing strands of information to determine
the fitness value of contacting another person or item
(Neuberg etal., 2011; Tybur & Lieberman, 2016). The
current findings demonstrate that interpersonal value
is one such strand. Other findings suggest that patho-
gen avoidance is relaxed in situations that require some
exposure to pathogens, such as sexual interactions
(e.g., Fleischman etal., 2015) and childrearing (e.g.,
Case etal., 2006). Future work can test whether relaxed
pathogen avoidance toward offspring and mates results
only from their high interpersonal value or whether
sexual value and genetic relatedness, which inform
interpersonal value (but are not redundant with it),
additionally shape pathogen avoidance (cf. Tooby etal.,
2008).
Second, researchers have speculated that people are
more disgusted by infection-risky contact with strangers
relative to friends because social familiarity is treated
as a cue to infectiousness, just as rashes and sores are
(Curtis etal., 2004; Peng etal., 2013; Stevenson & Repacholi,
2005). Similarly, the behavioral-immune-system litera-
ture is replete with proposals that prejudices toward
members of various groups partially stem from people
treating morphological features (e.g., in the cases of the
physically disabled, obese, and elderly) or foreign eco-
logical origin (e.g., in the case of immigrants) as cues
to infectiousness (for a summary, see Murray & Schaller,
2016). The current results suggest an alternative—or, at
least, supplementary—approach to understanding how
the behavioral immune system contributes to social
biases: Prejudices toward the aforementioned groups
might result from perceptions of interpersonal value
rather than perceptions of infectiousness. Recent stud-
ies has reevaluated claims that anti-immigrant preju-
dices partially result from perceptions that foreign
ecological origin is indicative of infectiousness (e.g.,
Karinen, Molho, Kupfer, & Tybur, 2019; van Leeuwen
& Petersen, 2018); future work could similarly clarify
whether the behavioral immune system outputs preju-
dices toward the obese, elderly, and physical disabled
because they are perceived as infectious or because
they are perceived as not offering the interpersonal
benefits that offset the infection risks posed by any
social interaction.
Third, if infection-risky contact is embraced with
interpersonally valued others and avoided with inter-
personally devalued ones, then contact rituals (e.g.,
hugs, handshakes) might be used to signal, regulate,
and maintain interpersonal valuation. Refusals to
engage in such rituals with a specific target might be
interpreted as suggesting that the target is not valued
enough to risk infection, is perceived as having some
symptom of contagious illness, or both. These consider-
ations might contribute to our understanding of the cul-
tural evolution and maintenance of greeting rituals. They
also highlight an important limit on the generalizability

Interpersonal Value and Pathogen Avoidance 1219
of these data, which were collected in the United States.
Recent findings suggest that at least some contamina-
tion aversion exists across human populations (Api-
cella, Rozin, Busch, Watson-Jones, & Legare, 2018).
Universality does not imply an absence of variation,
though. Indeed, some evidence suggests that potentially
infectious ritualized contact is less prevalent in areas
with more infectious disease (Murray, Fessler, Kerry,
White, & Marin, 2017). Any signal value of contact and
contact avoidance might similarly vary across regions
as a function of ecological parasite stress, as might the
degree to which interpersonal value influences motiva-
tions to embrace or avoid infection-risky contact. Even
within a single nation, the relation between interper-
sonal value and contact comfort might vary as a func-
tion of transient infection threats, such as those posed
by COVID-19.
Implications for the spread
ofinfectious disease
Multiple factors constrain the effectiveness of pharma-
ceutical interventions in combating pandemics. Hence,
outcomes of our battles against microbes will hinge on
the effectiveness of nonpharmaceutical interventions
(Ferguson etal., 2020). In addition to better hygiene
(e.g., handwashing), such interventions might focus on
stemming contagion within social networks. Indeed,
research during the 2009 H1N1 influenza pandemic
indicated that infectious disease spreads within social
networks much faster than it spreads across the broader
population (Christakis & Fowler, 2010). Closer physical
proximity and more frequent social interactions doubt-
lessly contribute to such spread. The current findings
reveal another factor that likely exacerbates within-
network contagion: the relaxation of pathogen avoid-
ance toward interpersonally valued targets. This
observation might help inform approaches to dampen-
ing disease transmission during outbreaks. Whereas
people need little encouragement to avoid infectious-
risky behaviors with most people, they largely feel com-
fortable engaging in identical behaviors with targets
that they especially value interpersonally. Improving
our understanding of this and other features of the
behavioral immune system can enable a better defense
in our war against infectious disease.
Transparency
Action Editor: Eddie Harmon-Jones
Editor: Patricia J. Bauer
Author Contributions
J. M. Tybur developed the study concept, coordinated data
collection, and drafted the manuscript. J. M. Tybur designed
Study 1; J. M. Tybur and T. R. Kupfer designed Study 2; and
J. M. Tybur, T. R. Kupfer, D. Lieberman, and R.E. de Vries
designed Study 3. L. Fan analyzed the data under the super-
vision of J. M. Tybur. All authors provided critical revisions
on the initial draft of the manuscript. All authors approved
the final version of the manuscript for submission.
Declaration of Conflicting Interests
A percentage of profit received from commercial sale of
the HEXACO personality inventory is used by the Vrije
Universiteit Amsterdam to support research by the last
author. The authors declared that there were no other
potential conflicts of interest with respect to the authorship
or the publication of this article.
Funding
This research was supported by Horizon 2020 European
Research Council Grant StG-2015 680002-HBIS.
Open Practices
All data, analysis scripts, and materials have been made
publicly available via OSF and can be accessed at https://
osf.io/4agk8/. The design and analysis plans for all three
studies were preregistered at https://osf.io/4agk8/. The
complete Open Practices Disclosure for this article can be
found at http://journals.sagepub.com/doi/suppl/10.11
77/0956797620960011. This article has received the badges
for Open Data, Open Materials, and Preregistration. More
information about the Open Practices badges can be found
at http://www.psychologicalscience.org/publications/
badges.
ORCID iDs
Joshua M. Tybur https://orcid.org/0000-0002-0462-6508
Lei Fan https://orcid.org/0000-0002-3531-9199
Supplemental Material
Additional supporting information can be found at http://
journals.sagepub.com/doi/suppl/10.1177/0956797620960011
Note
1. In each study, the main effect of target sex on contact comfort
was qualified by an interaction with participant sex. Further
details are provided in the Supplemental Material.
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