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Journal
of
Comparative
Psychology
1994, Vol. 108,
No. 3,
233-242
Copyright
1994
by the
American
Psychological
Association,
Inc.
0735-7036W/$3.00
Human (Homo
sapiens}
Facial
Attractiveness
and
Sexual
Selection:
The
Role
of
Symmetry
and
Averageness
Karl
Grammer
and
Randy
Thornhill
We
hypothesized
from
the
parasite
theory
of
sexual
selection
that
men
(Homo sapiens) would
prefer averageness
and
symmetry
in
women's faces, that women would prefer averageness
and
symmetry
in
men's
faces,
and
that women would prefer largeness (not averageness)
of the
secondary sexual traits
of
men's faces.
We
generated computer
images
of
men's
and
women's
faces
and of
composites
of the
faces
of
each sex,
and
then
had men and
women
rate
opposite-sex
faces
for 4
variables (attractive, dominant, sexy,
and
healthy). Symmetry, averageness,
and the
sizes
of
facial features were measured
on the
computerized faces.
The
hypotheses were supported,
with
the
exception
of the
hypothesized
effects
of
averageness
of
female
and
male
faces
on
attractiveness ratings.
This
is the first
study
to
show that facial symmetry
has a
positive
influence
on
facial attractiveness ratings.
Although
adult facial attractiveness ratings
are
replicable,
even
cross-culturally
(see reviews
and
discussions
in
Jones
&
Hill, 1993,
and
Langlois
&
Roggman,
1990), there
has
been considerable controversy around attempts
to
identify
in
research
the
facial features that actually cause faces
to be
judged attractive
or
unattractive.
As
discussed
by
Langlois
and
Roggman, studies
of
individual
facial
features
(e.g.,
nose size)
often
have yielded inconsistent results between
studies. Faces created
by
combining individual faces into
composites have been shown
to be
more attractive than
the
individual
faces, which
is
felt
to be a
preference
for
average
facial
features (Langlois
&
Roggman, 1990; Symons,
1979). Averageness
effaces
can be
calculated metrically
or
constructed
photogrammetrically.
Gallon
(1879) con-
structed composites
of
individual pictures with
the
photo-
graphic
method
of
simply projecting them
one
over
the
other
on a
negative. According
to
Gallon,
this method
"enables
us to
obtain with mechanical precision
a
general-
ized picture;
one
that represents
no man in
particular,
but
portrays
an
imaginary
figure
possessing
the
average features
of
any
given group
of
man"
(1879,
p.
341).
Indeed,
Treu
(1914)
had the
impression that these composites
are
"sin-
gularly
beautiful"
(p.
441). However,
as
Alley
and
Cunning-
ham
(1991;
see
also Benson
&
Perrett,
1991) pointed out,
composites
are
also more symmetrical
and
rather
free
of
Karl
Grammer,
Ludwig
Boltzmann
Institute
for
Urban
Ethology,
Vienna,
Austria;
Randy
Thornhill,
Department
of
Biology,
Uni-
versity
of New
Mexico.
We
thank
Klaus
Atzwanger,
John
Dittami,
Steve
Gangestad,
Joy
Ingram,
Kurt
McKean,
and Don
Symons
for
helpful
comments
on
the
research.
Randy
Thornhill
thanks
Klaus
Atzwanger
and
John
Dittami
for
their
hospitality
in
Vienna.
Anne
Rice's
help with
the
preparation
of the
article
is
appreciated.
Correspondence
concerning
this
article
should
be
addressed
to
Karl
Grammer,
Ludwig
Boltzmann
Institute
for
Urban
Ethology,
Althanstrasse
14,
A-1090
Vienna,
Austria
or to
Randy
Thornhill,
Department
of
Biology,
University
of New
Mexico,
Albuquerque,
New
Mexico
87131-1091.
Electronic
mail
may be
sent
to
rthorn@carina.unm.edu.
facial
blemishes,
and
therefore
one of
these traits, rather
than averageness
per se, may be the
cause
of the
enhanced
attractiveness
of
composites.
In
addition, Alley
and
Cun-
ningham
emphasize that there
is
considerable evidence
(e.g.,
Keating, 1985) that
the
most sexually attractive male
faces
are
those that show extremes,
not
averageness,
in
certain features (e.g., wide jaw),
felt
to be
perceived
as
dominance indicators.
Our
study
of the
cross-sex attractive-
ness ratings
of
faces
of
both sexes attempts
to
clarify
adult
facial
beauty
by
examining
the
roles
of
facial symmetry
and
averageness
and
their interaction
with
individual dimen-
sions
of the
face.
We
use the
theoretical framework
of
sexual selection.
The
prominent theory
of
sexual selection
is the
parasite theory,
which proposes that sexual selection favors those traits that
advertise resistance
to
parasites, both
microparasites,
such
as
bacteria
and
viruses,
and
macroparasites,
such
as
nema-
todes
and
protozoa (Hamilton
&
Zuk, 1982). There
is
con-
siderable evidence that parasite-resistant organisms
win in
competition
for
mates, both
in
intrasexual
competition (usu-
ally males competing
for
females)
and in
being
chosen
by
the
opposite
sex and
that secondary sexual traits advertise
parasite resistance (see partial reviews
in
Hausfater
&
Thornhill, 1990,
and
Zuk,
1992).
According
to the
parasite
theory
of
sexual selection, mate choice decisions include
medical examinations
of
potential mates,
and
parasite-
resistant
organisms
are
preferred
because
they
produce
ge-
netically
resistant
offspring
or
provide better parental care
to the
offspring.
Thus,
the
parasite theory proposes that
beauty
of
bodily
form
is
perceived
as a cue to
high parasite
resistance
by
animals
in
choosing mates.
Secondary sexual characters
are
evolved outcomes
of
sexual
selection. There
is a
link between parasite resistance
and
secondary sexual traits because
sex
hormones, espe-
cially
testosterone, lower
immunocompetence
(Folstad
&
Karter,
1992;
Wedekind,
1992). Whereas high
liters
of
testosterone
are
necessary
for the
production
of
large sec-
ondary
sexual trails, there
will
necessarily
be a
positive
correlation between developmenl
of
secondary sexual
233
234
KARL
GRAMMER
AND
RANDY
THORNHILL
traits
and the
quality
of the
immune system; only healthy
organisms
can
afford
the
high testosterone handicap
on
the
immune system that
is
necessary
for the
production
of
elaborate sexual traits (Folstad
&
Karter,
1992).
The hu-
man
face contains secondary sexual traits, that
is,
facial
features
that develop
or
increase
in
size
at
puberty under
the
influence
of the sex
hormones,
androgens
and
estro-
gens. Enlarged jaws, chins,
and
cheekbones
in men are
examples
of
facial secondary sexual traits that
are
influ-
enced
by
testosterone
(Enlow,
1990; Tanner, 1978),
and
Thornhill
and
Gangestad
(1993) hypothesized that large-
ness
in
these features
are
considered sexually attractive
because
of
advertised immunocompetence.
Genetic diversity
may be an
important defense against
parasites, both
at the
between-organisms level (i.e.,
the
population
level)
and at the
within-organisms level (see
review
in
Thornhill
&
Gangestad, 1993;
see
also Hamilton,
1982; Tooby, 1982). Within-organisms genetic diversity
is
dependent
on
individual genetic
heterozygosity.
For
herita-
ble
traits that
are
continuously distributed, heterozygosity
correlates positively
with
average trait expression
(Soule
&
Cuzin-Roudy,
1982). Facial attractiveness
is
continuously
distributed
and
probably
is
heritable (see Thornhill
&
Gangestad, 1993). This implies that average values
of
facial
features
reflect high heterozygosity. Thus, Thornhill
and
Gangestad hypothesized that facial averageness
is
attractive
because
of its
association with heterozygosity
and
thus
parasite
resistance. This hypothesized pattern
may
primarily
apply
to
female faces.
The
intrasexual sexual competition
component
of
sexual selection involving dominance
and
combat
has
worked more strongly
on
males than
on
females
in
human evolutionary history (Darwin,
1871;
Symons,
1979),
and
male faces have multiple, testosterone-facilitated
secondary sexual traits (viz., adult male chin, cheekbones,
brow
ridge, and
jaw) that
are
expected
by the
parasite theory
to
have evolved
to
signal health-related dominance
b