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To investigate the effects of stress on men’s preferences
for similar versus dissimilar mates, we used a set of erotic
pictures of female nudes that were computer-modified to* Author for correspondence (lass1302@uni-trier.de).Received
AcceptedKeywords: mate choice; facial self-resemblance; stress; cold-pressor test; startle
ODUCTION
is a central aspect of human and animal life, and
tudies have investigated how humans and animals
their mating partners. In humans, one of the most
tly investigated topics is the preference for similar
dissimilar mates. Studies have shown that human
ic partners tend to resemble each other in many
including facial characteristics (Griffths & Kunz
Zajonc et al. 1987; Bereczkei et al. 2002, 2004).
ly, we also showed a preference for similar mates
experimental manipulation of facial resemblance
ennemann et al. submitted). Overall, experimen-
ence indicates a preference for self-resembling
even though there is one study that showed a pre-
for dissimilar mates specifically for short-term
ships (DeBruine 2005).
ever, mating preferences are also context-
ent, and one factor that has repeatedly been
to alter mate choice in animals is stress. Stress is
ptive response that is typically thought to enhance
bability of survival in the face of threat, but it is
ing apparent that stress is also associated with
behaviour and mate choice. For example, corticos-
(a hormone released in response to stress) has been
to reduce male odour preferences in female mice
has shown that stress alters the mating preferen
stalk-eyed flies, which show less preference for
attractive mates and a willingness to mate with less
tive mates than do non-stressed animals (Lopez
Hingle et al. 2001). These studies seem to indica
stressed animals lose their ‘normal’ mating prefere
However, the effects of stress on human mating p
ences have not yet been investigated. From the a
studies described above, one could expect that h
also simply lose their preference for similar mates
stress. However, life-history theory (Stearns 1992
dicts that the optimal reproductive strateg
individuals in stressful environments is to ma
current reproduction to minimize the chances of l
extinction. Having short-term relationships inste
long-term relationships is a way of increasing c
reproduction and it has been shown that indiv
who experience psychosocial stress have more shor
relationships than do individuals without a hist
psychosocial stress (Koehler & Chisholm 2009
described above, Debruine (2005) found a pref
for dissimilar mates in the context of a shor
relationship. Therefore, one might also argue
stress not only decreases mating preference for s
mates, but also increases mating preference for dissunstressed individuals showed the expected preference for similar mates, but stressed individuals seemEffects of stress
preferences: stress
dissimil
Johanna Lass-Hennemann1,*, Ch
Andre´ Schulz1, Terry D. Blumen
1Institute of Psychobiology, Un
2Department of Psychology, Wake Fore
Although humans usually prefer mates that resemb
text. Stress has been shown to alter mating prefer
mating preferences are unknown. Here, we inve
self-resembling mates. Participants first underwen
procedure. Then, participants viewed either neutr
facial characteristics were computer-modified to re
or were not modified, while startle eyeblink resp
were rated as being pleasant, and reduced startle
control group, startle magnitude was smaller dur
resembling female nudes compared with other-res
nudes, indicating a higher approach motivation t
magnitude was larger during foreground presenta
other-resembling female nudes and non-manipu
motivation to dissimilar mates. Our findings sh8 February 2010
19 February 2010 2175n human mating
individuals prefer
mates
tian E. Deuter1, Linn K. Kuehl1,
al2 and Hartmut Schachinger1
rsity of Trier, Trier, Germany
niversity, Winston-Salem, NC, USA
themselves, mating preferences can vary with con-
es in animals, but the effects of stress on human
ated whether stress alters men’s preference for
cold-pressor test (stress induction) or a control
ictures or pictures of erotic female nudes whose
ble either the participant or another participant,
es were elicited by noise probes. Erotic pictures
agnitude compared with neutral pictures. In the
foreground presentation of photographs of self-
bling female nudes and non-manipulated female
elf-resembling mates. In the stress group, startle
of self-resembling female nudes compared with
ed female nudes, indicating a higher approach
that stress affects human mating preferences:
Proc. R. Soc. B (2010) 277, 2175–2183
doi:10.1098/rspb.2010.0258
Published online 10 March 2010This journal is q 2010 The Royal Society

female and fitted to the body of the erotic female nude,
2176 J. Lass-Hennemann et al. Stress influences mating preferencesresemble either the participant or another participant. We
employed two independent methods to measure men’s
sexual attraction to the different erotic picture categories,
subjective valence and arousal ratings of the erotic pic-
tures, and affective startle response modulation.
Affective startle modulation is a well validated and
widely used method for assessing affective valence in the
laboratory (Bradley et al. 1999). Numerous studies have
shown that the startle reflex (elicited by a brief burst of
noise) is facilitated when people view aversive pictures
and inhibited when people view pleasant (especially
erotic) pictures (Bradley et al. 2001). Viewing of aversive
pictures leads to an activation of the defensive system and,
therefore leads to an augmentation of the congruent
defensive startle reflex. Viewing of pleasant pictures, on
the other hand, engages the appetitive/approach system
and leads to an inhibition of the non-congruent defensive
startle reflex. Thus, affective startle modulation is not a
direct measure of the physiological mechanisms under-
lying emotion, but rather an indirect measure of the
activity of neurobiological structures involved in the pro-
cessing of approach and withdrawal motivation. The
inhibition of the startle reflex while viewing pleasant pic-
tures reflects the activity of neurobiological circuits
involved in approach motivation.
Affective startle modulation has been shown to gener-
alize to a variety of foreground stimuli other than pictures
that modify the emotional state of the participants
(Bradley et al. 1999), and eliciting the startle response
during foreground presentation of different stimuli
serves as a validated measure of the affective valence of
the presented stimuli. In particular, the startle modu-
lation paradigm has been frequently used to analyse
affective valence of and approach motivation to erotic pic-
tures and film segments (Koukounas & Over 2000;
Koukounas & McCabe 2001; Prause et al. 2008;
Lass-Hennemann et al. 2009, submitted). Therefore,
affective startle modulation appears to be an appropriate
measure to evaluate how stress influences the attractive-
ness of, and approach motivation to, photographs of
erotic female nudes. We used the affective startle modu-
lation paradigm in addition to subjective ratings,
because in previous studies it has served as a more sensi-
tive measure for approach and withdrawal motivation
than subjective ratings (Levenston et al. 2000; Lass-
Hennemann et al. 2009, submitted). Subjective ratings
are a voluntarily controllable measure, one that may be
confounded by person variables such as social desirability
and demand characteristics, while the startle response is a
pre-attentive measure of approach motivation that is not
easily controllable by the participant.
In our study, participants first underwent a stressful
procedure or a non-stressful control procedure. Then,
participants viewed pictures of erotic female nudes
whose facial characteristics were either computer-
modified to resemble the participant, or made to resemble
another person, or were not manipulated, as well as
viewing neutral pictures.
Based on previous research (Lass-Hennemann et al.
submitted), we predicted that non-stressed participants
would show a preference for similar mates, as indicated
by decreased startle magnitude in the presence of pictures
of self-resembling erotic female nudes. We predicted that
stressed participants would not show the usual preferenceProc. R. Soc. B (2010)even though it had a subtle resemblance to the participant.
For further details on the underlying technology, see
Tiddeman et al. (2001). No participants reported detecting
the nature of the experiment, suggesting that the morphing
did not result in conscious recognition of their own face by
any participant.for similar mates, but instead a preference for dissimilar
mates, as indicated by an inhibition of startle magnitude
(indicating approach motivation) in the presence of
pictures of other-resembling female nudes and non-
manipulated female nudes.
2. MATERIAL AND METHODS
(a) Participants
Participants were 50 male heterosexual students at the Uni-
versity of Trier, Germany, who responded to notices
offering 25E for taking part in two different experiments.
Participation was limited to heterosexual Caucasian stu-
dents without beards, piercings or tattoos in the facial
region. Furthermore, only participants with normal or cor-
rected to normal vision and no history of hearing problems
were included in the study. Participation was also limited to
healthy non-smokers with body mass index in the normal
range of between 20 and 25 kg m2. Exclusion criteria
were determined by a telephone screening interview that
the respondent completed before being invited to take
part. We also required participants to refrain from physical
exercise, alcohol, caffeinated drinks and meals within 3 h
prior to each of the two experimental sessions. The
research was approved by the responsible local ethics com-
mittee, and all participants gave their written informed
consent.
(b) Materials and design
Experimental material consisted of 40 pictures, 30 of which
showed erotic female nudes with a completely visible face
(i.e. no hair covering parts of the face), a direct gaze at the
observer and a neutral facial expression. The other 10 pic-
tures were neutral pictures selected from the International
Affective Picture System1 (household objects) (Lang et al.
1999).
We used computer imaging techniques to manipulate
facial resemblance between pictures of the face of each par-
ticipant and the faces of the pictures of the erotic female
nudes. The pictures of the erotic female nudes formed the
basis for the morphing procedure, in which the face of the
participant was morphed into the face of the erotic female
nude (figure 1). Templates were created that specified the
contours and certain landmarks on each face. The morphing
routine itself comprises two processes: a shape morph
averages the distance between the features of both faces
that were specified in the template and a colour morph
averages the colours of each pixel. These processes result in
two different output images, and the colour morph was
used as a layer on top of the shape morph. To ensure that
the resulting female nude pictures still looked attractive and
feminine, transparency was added to the colour morph
layer to a 30 per cent degree. This means that the morphed
picture shared 50 per cent of the shape of the participants’
face, but only 30 per cent of the colour information. By
doing this, a composite face was created which was in
favour of the women’s features, i.e. the face was still primarily