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Part III
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Psychological Aspects of Disease
Aspects ofFacial Esthetics
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andDisgurement
ChristophRunte andDieterDirksen
14
14.1 Introduction
Why do human faces look the way they do? And
how do we judge attractiveness? Still we do not
have nal answers to these and related questions
[1, 2], but recently, science has at least found
some clues.
Through the centuries, there have been many
attempts to nd out how beauty in general and
beauty of the human face in particular are determined. Beauty has been equated with truth [3],
usefulness [4], and good [5]. The French novelist Marie-Henri Beyle, better known as Stendhal,
noted beauty was nothing other than the “promise of happiness” [6], which means that we are
attracted to objects or persons which might help
us to get happy, and this attraction is what we
call beauty, but this only shifts the problem to
the denition of happiness. If happiness is to
live in the company of trustworthy [7], healthy
[8], and guiding [9] people, faces are believed to
reveal those qualities [10]. Evolutionary biology
would explain beauty, or, strictly speaking,
attractiveness, mainly with regard to mate selection as a product of selection by survival and
sexual selection. Another evolutionary aspect of
beauty and disgurement is its inuence on
parental care [11, 12]. There have been attempts
C. Runte (*) · D. Dirksen
Department of Prosthodontics, University of Münster,
Münster, Germany
e-mail: crunte@uni-muenster.de
to describe beauty as a consequence of the adherence to objective morphologic parameters, e.g.,
bilateral symmetry and certain proportions.
Other authors countered that the beauty of a person or an object might be judged differently by
different persons, which leads to the conclusion
that beauty is “not judged objectively but according to the beholders estimation” (Theocritus
[13]). In his Critique of Judgment, Immanuel
Kant [14] dened beauty as something causing
pleasure without any interest and understanding.
Kant then continued that if beauty was caused by
the pleasing perception without personal interest, it should be pleasing to every beholder.
Therefore, beauty as a universally pleasing perception would be mistaken as a logically deducible quality of the object. However, later
philosophers dismissed Kant’s idea of pleasure
without interest.
After all these attempts, still there seems to be
no simple explanation or geometrical formula to
dene beauty in detail, and, as many people agree
in their esthetic judgment on who is attractive and
who is not, beauty seems not only to depend on a
beholders’ free and unconditioned estimation.
An individual, intuitive judgment of beauty in
general seems to be determined by the process of
visual perception, sociocultural conditions, and
individual experience. Chelsea Wald [2] recently
summed up four fundamental open questions on
beauty, starting with the problem of its denition:
“What is the point of human beauty?”
© Springer Nature Switzerland AG 2021
U. Meyer (ed.), Fundamentals of Craniofacial Malformations,
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Beauty and disgurement are often used as
opposites, as we did in the chapter title. However,
disgurement and beauty are not mutually exclusive. If beauty is at least partially judged by the
beholder, its opposite would also be subject to the
beholder’s estimation. Disgurement is as difcult to dene as it is true for beauty. If we use
disgurement as the opposite of the given denitions of beauty, disgurement could be dened as
equal to falsity, futility, and bad. It could be
described as the “promise of bad luck” or the violation of proportional rules. As an opposite of
Kant’s denition, disgurement would be a perception that is unpleasant without interest and
understanding. None of these denitions is truly
convincing.
14.2 Biological Aspects ofFacial
Beauty andDisgurement
As it has been said before, beauty may be seen as
an aspect of perception (“in the eye of the
beholder”) or as a result of certain morphologic
properties. We will therefore discuss these
aspects of perception and of morphogenesis in
more detail.
14.2.1 Visual Perception andits
Inuence ontheEsthetic
Judgment
All humans share fundamental physiologic processes of visual perception and recognition.
Visual perception and recognition enable us to
experience the world around us, beginning with
the faces of our parents. It is necessary to understand these processes because they are the reason
why our visual perception is selective and also
why our judgment of the beauty of a face is not
free and according to our individual assessment.
The rst step of visual perception is light
entering the eye bulb through the lens and being
projected to the retina. Here, the photon energy is
transformed into chemical energy. Illuminated
rhodopsins activate G-proteins, which then start
the signal transduction. At this stage the signal
represents an excitation at a specic point of the
two-dimensional retina with information on location, brightness (rods and cones), and color
(cones). Passing through the layer of retina bipolar cells, the signals of a number of photoreceptors from a receptive eld are collected by a third
neuron (retinal ganglion cell). There are different
types of retinal ganglion cells; on-cells will transmit a signal with a higher ring rate if the input
signal from center of the receptive eld is more
intense than in the peripheral areas. Off-cells
would show a reverse reaction. The ganglion cell
axons follow the optical nerve with the information from the median part of the retina crossing to
the contralateral hemisphere (chiasma opticum)
while the information from the lateral part
remains on the same side.
The next signal transformation step (located in
the corpus geniculatum laterale) is an extraction
of edges or outlines with a high contrast. The
visual information is then projected primarily to
the occipital visual cortex. The signal transformation to outlines is illustrated in Fig. 14.1.
Understanding of this fundamental process of
visual perception was founded in the late 1950s
by David Hubel and Torsten Wiesel with their
experiments on the cat’s striate cortex [15].
Larsson et al. [16] conrmed the account of
structures with high contrast to pattern recognition. However, the ability to recognize faces with
only a few outlines from a sketch or even from
randomly distributed elements has been well
known for centuries. In his treatise on painting,
Leonardo da Vinci [17] claimed that “by looking
attentively at old and smeared walls or stones and
veined marble of various colors, you may fancy
that you see in them several compositions, […
and] strange countenances […]. By these confused lines the inventive genius is excited to new
exertions.”
Efferences from the corpus geniculatum laterale also reach the superior collicles, which are
important for eye movements. They send signals
to nuclei of the cranial nerves (esp. oculomotor,
trochlear, and abducens nerve) and the pulvinar
(central medial, posterior inferior, and middle
inferior pulvinar nuclei [18]). If a visual stimulus
is presented, the following eye movements are
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Fig. 14.1 Steps of visual perception simulated by digital
image processing– original picture (left), the signal highpass ltered and posterized (middle) and reduced to areas
below a brightness threshold (right). By these simple procedures, the image is reduced to lines indicating the contours, but recognition of the object is still possible. Data is
correspondingly reduced from 389KB (.tif-format, LZWcompressed le from left image) to 90KB (same format,
right). With similar procedures, visual recognition is
directed in a way to “track” the areas of high
brightness contrast. This “tracking” was examined and described by Alfred Yarbus [19], who
also identied a special area of interest within the
face, called the “Yarbus triangle.” This triangle is
dened by the eyes and mouth (Fig. 14.2).
Consequently, Karl Popper and John Eccles [20]
compared the process of visual perception to the
painting of a picture, not to the taking of a photograph. Subsequent studies showed that there is
also a dominance of the left “eld of gaze” [
21] if
we are looking at a face. There was no preference
of one side of the eld of gaze when looking at
other, nearly symmetrical gures. Thus, the right
side of the face might have more impact on the
esthetic judgment than the left one. Interestingly,
Meyer-Marcotty et al. [22] found that subjects
affected by cleft lip and palate focus their attention on the upper lip and nose if they look at the
faces of healthy persons.
Visual stimuli showing regular geometry [23],
reection symmetry [24], familiar shapes, or
matching expectations [25, 26] are supposed to
focused on contour lines. These lines are not restricted to
physical boundaries of the object. Lines of contrast can
also be caused by color or material changes and by lighting and reection at curvatures and edges, e.g., at the eyelids, nose, ears, and philtrum. The pictures of Nefertiti
were generated using the 3D model “bust of Nefertiti at
the Neues Museum, Berlin” (
com/object/3d- print- bust- of- nefertiti- at- the- egyptianmuseum- berlin- 2951)
Fig. 14.2 The Yarbus triangle is a region of the face
where structures with high contrast are more frequently
focused than other regions. In his original publication
from 1967, Yarbus [19] used pictures from faces and also
one from a bust of Nefertiti (in prole) and simultaneously recorded the eye movements. With his technique, he
could superimpose eye movement tracing with the visual
stimuli
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C. Runte and D. Dirksen
draw the viewer’s attention to themselves, especially if they show clearly visible outlines within
the Yarbus triangle.
In recent studies it was shown that perception
of faces is different from perception of other familiar objects in view. A fast and intense neuronal
response to visual stimuli called the N170 effect is
selective for faces in certain areas of the brain [27].
The source of this neuronal response to the presentation of faces is located primarily in the right fusiform and infratemporal gyri, especially in regions
called inferior occipital gyrus face area (OFA) and
fusiform face area (FFA, [28]). Damage or intracranial stimulation of the FFA is associated with
the disability to recognize faces (prosopagnosia,
[29]). However, these areas are only part of a dis-
tributed neural network responsible for face recognition [30]. Prosopagnosia can also be caused by
injuries of the temporal lobe, e.g., after surgical
treatment of epilepsia. Recent studies indicate that
the ventral anterior temporal lobe plays an important role in person-specic face perception [31].
However, the question how the different parts of
our brain inuence our esthetic judgment in detail
remains largely unanswered.
Our knowledge on visual perception suggests
that the fundament for our esthetic judgment is
focused on facial structures, especially those
within the Yarbus triangle, showing clear outlines
of high contrast. As a consequence, these structures will be of importance in the denition of
beautiful properties, e.g., using facial proportions.
However, the determination of an objects’
physical shape is only the start of a process of
recognition and assessment. Eleanor Rosch [32,
33] tested older concepts of Gestalt psychology
experimentally and found that there are “ideal
types” of perceptual stimuli, e.g., colors. These
prototypes represent the “clearest cases, best
examples” of a category (“a concept designatable
by words”). A perceptual stimulus is therefore
evaluated by comparison to the prototype of its
category [1]. Whether a visual stimulus will
cause pleasure or disgust will therefore largely
depend on its categorization. For example, one
person might react with disgust to the view of an
oyster, another one with pleasure. The difference
cannot be explained by the shape or texture of the
oyster itself, but by the presentation and the per-
sonal experience one (or her/his social environment) has with oysters and if it is reasonable to
categorize the oyster as delicacy. Tattoos and
piercings have been held in very different degrees
of regard in different times and cultures.
Examples from the orofacial region are “decorative crowns” and “dental grills” among certain
ethnic groups and cultural scenes [34]. The polished metallic surfaces of crowns or amalgam
llings found their own esthetic reverence in dental professionals in the past. However, this assessment was not always shared by patients. The
more natural look of composite resins and
ceramic veneers changed the view on metallic
restorations. Within one category, perceptual
stimuli are compared to the prototype. It has been
assumed that the closer the stimulus ts to the
prototype, the more pleasing it will be. On the
other hand, typical stimuli are assumed to be
more difcult to remember [35].
Classifying human beings into categories,
especially by a look at their face, is problematic.
Racism, nationalism, and class consciousness are
only a few and extreme examples for the classication connected to discrimination. At least, conscious or unconscious classication will have a
great inuence on our esthetic judgment.
Prototype theory assumes that objects or subjects
will cause pleasure if they are “prototypical” for
their category [1].
When a visual stimulus has been matched to
the category “face.” studies of Oosterhoff and
Todorov [36] suggested that it will be evaluated
basically on the two dimensions, “valence” and
“dominance.” Thus, the beholder gathers information from facial cues whether the person
approaching is harmless or harmful and physically capable of implementing his intentions.
These cues can be found mostly in the eye and
mouth region, e.g., if the eyebrows are lifted, the
resulting signal is trustworthiness.
14.2.2 Evolutionary Biology, Beauty,
andAverageness
Facial morphogenesis, the inuence of facial
properties on mate selection and parental care,
and the inheritance of genes regulating them are
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219
connected by the complex mechanisms of evolutionary biology. A current publication by Xiong
etal. [37] listed a number of gene loci associated
with different facial proportions within the Yarbus
triangle. Although there still are many open questions on human facial morphogenesis and how it
has evolved, a simple example may illustrate
some of the possible ways of facial development
over generations. Stalk-eyed ies exhibit bizarre
head morphology [38]. Arthropod body plan is
very different to the human one, but evolutionary
mechanisms are the same. Although it has been
assumed that a wider interocular distance would
be benecial in stereoscopic viewing (Fig.14.3),
this argument is not convincing, as there are also
drawbacks like the necessity to calculate an
increased parallaxis for spatial perception and
possible handicaps in ight. However, there is
evidence for a connection between a large eyespan and “good genes” as only ies in good condition develop wide eyespans. If a wider eyespan
is a signal for “good genes,” the idea of female
ies preferring male ones with a wider interocu-
lar distance would be convincing (Fig.14.4). A
third mechanism is caused by an X-chromosomal
meiotic drive that can be suppressed by genetic
factors associated with male y wide eyespan
(Fig.14.5).
Evolutional biology would suggest that an
advantageous feature would automatically become
the average by elimination of other variants.
However, a connection between beauty and
averageness has been postulated even before
Darwin’s publications. In his Critique of
Judgment, Kant [14] described how he thought
our perception of beauty was inuenced by the
average image of our visual experiences: He
described how our imagination recalls form and
view of a subject and is capable of “adding” all
views of a certain kind, e.g., of a man. And to
his belief, somebody who has seen a thousand
men can estimate the average stature by superimposing a lot of or even all of the thousand
images in his mind. The outlines of the average
man would then also represent the stature of a
beautiful man.
Natural selection
by survival:
Narrow interocular
distance is associated
with lower cahnce
of survival
Next Generation
with higher proportion of genes
from male files with longer
interocular distance
Fig. 14.3 Stalk-eyed ies exhibit unusual facial proper-
ties with exaggerated eyespan (schematic representation).
This was assumed to be a result of functional adaptation
caused by an improved stereoscopic perception advanta-
geous for survival, but the more convincing explanation is
that only ies in good condition (with “good genes”)
exhibit a wide eyespan. Thus, a wide eyespan is not the
reason for but the result of an advantage in survival
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Natural selection
by survival:
Interocular distance has
no influence on survival
(or larger eyespan is
even disadvantageous)
Next Generation
with higher proportion of genes
from male files with longer
interocular distance
Fig. 14.4 Another mechanism is sexual selection. In this example, female ies preferably choose male ies with wider
eyespan as mates
Female files prefer male ones
sexual selection:
with larger eyespan
C. Runte and D. Dirksen
Superimposition of images became possible
with the introduction of photography in the nineteenth century. In 1883, Francis Galton [39] published his Inquiries into Human Faculty and Its
Development. He observed that “All composites
are better looking than their components, because
the averaged portrait of many persons is free
from the irregularities that variously blemish the
looks of each of them.”
Evolutionary biology can explain a connection between facial attractiveness and averageness, following two basic concepts: On the one
hand, average shapes could simply be the features of the most successful subjects (Fig.14.6).
On the other hand, subjects with attractive facial
features should have a higher reproductive success (Fig.14.7). However, being attracted to certain facial shapes that are signs of success (sign
for “good genes”) would be an advantageous
strategy in mate choice, and these properties
would prevail over the generations.
In addition to “survival of the ttest” and
“reproduction of the most attractive,” there are
even more evolutionary mechanisms to be taken
into consideration. If a small population gets isolated, e.g., on a distant island, and an aboveaverage number of individuals bearing certain
“founder mutation” passes through this evolutionary “bottleneck,” the following generations
will show a high percentage of this mutation and
also a reduced genetic variation (Fig.14.8), even
though this mutation might be indifferent to survival or reproduction.
Beauty may be determined by our visual experience of our own local social and cultural environment. The faces we see share some common
properties, characteristic for our ethnic group.
We get used to those properties and check
whether they can also be found within a stranger’s face. Sociocultural factors inuence our
judgment of those faces, e.g., watching a movie
like Beauty and the Beast might inuence a
child’s judgment on beauty and ugliness. If certain properties of the face are associated with a
higher social status or cultural or religious value,
it may lead to a higher reproductive success. If
there is no or only limited viability drawback,
even a small reproductive advantage connected to
Female population has
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Natural selection
by survival:
Interocular distance has
no influence on survival
(or larger eyespan is
even disadvantageous)
Wide eyespan genotype also
has property of suppressing
female meiotc drive gene
Next Generation:
No male descendants from
male flies with short
interocular distance
221
X-chromosal
meiotic driver which causes
sperms with Y-chromosome
to degenerate
sexual selection:
No preference
regarding eyespan
Fig. 14.5 In stalk-eyed ies, a meiotic drive gene has
been identied. This meiotic drift causes sperms with
Y-chromosome to degenerate. In this model, male ies
with wide eyespan have the potential to suppress the mei-
a facial feature might be sufcient to elicit a
higher frequency. This mechanism is called “cultural selection” and has, e.g., been discussed as
another possible reason (apart from the founder
effect) associated with a higher prevalence of
albinism in Native American people [40].
Superimposition of images to nd an average
face from a dened population was performed,
e.g., by Perrett etal. [41], using vectorized outlines from portrait photographs. However, they
connected the faces to degrees of attractiveness
judged by a number of observers, and with these
data they were able to identify facial properties of
more attractive subjects. They could, by exaggerating the difference between the average face of
otic drift gene, those with a narrow interocular distance
have not. Real stalk-eyed ies in addition exhibit sexual
preference for large eyespan
all subjects and the average of the most attractive
faces, create a “super-beauty.”
In contrast to beauty, facial disgurement
frequently causes a feeling of disgust [42, 43].
To explain avoidant behavior with unhealthy or
poisonous dishes or drinks with evolutionary
biology is suggesting itself. Evolution biology
would likewise provide an obvious explanation
for the behavior of keeping a healthy distance
to persons who exhibit signs of a contagious
disease. However, any threatening exposition or
phenotypic trait can be to the detriment of the
organism by reducing the probability to survive
or to reproduce, indifferent or even an advantage for an organism by surviving and by this
222
Given population with
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C. Runte and D. Dirksen
variability in one feature
(interocular distance).
Average face
Feature has no influence on
Natural selection
by survival:
Narrowed means less
stereoscopic perception
Survivors
(may also predominantly
carry genes that
determine preference of
partner with wider
interocular distance)
Fig. 14.6 Averageness as a result of evolution by “sur-
vival of the ttest.” In this example, a narrowed interocular distance would be a drawback in spatial perception.
attractivity and
reproductive success
New average face
Another important factor for survival would be the induction of parental care by cuteness
proving the higher qualication to survive, i.e.,
the “good genes.” In fact, even an obvious facial
disgurement has been discussed as benecial
from evolutionary biology’s perspective: Acne
has been hypothesized as an evolutionary
mechanism of protection while being at an
immature age [44].
As a conclusion, it can be summarized that
evolutionary biology gives good and reasonable
explanations for many phenomena, but instead of
simple chains of causation, it offers several
mechanisms for the selection of facial properties,
beauty, and disgurement. Some traits of the
human face may not have evolved by a process of
adaptation but as a genetic by-product of another
process. As long as not all factors and their interactions are understood, attempts to explain
aspects of beauty of the human face by a simple
chain of causation would be speculative.
14.3 Beauty andFacial Symmetry
In mathematical terms, symmetry is the property
of an object to be invariant to certain transformations: reection, rotation, scaling, and transla-
Given population with
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One variation (red hair) is
Natural selection
Feature has no
influence on survival
223
variability in one feature
(color of hair).
Average face
predominantly chosen
as partner due to
increased attractivity
Survivors
(may also predominantly
carry genes that
determine preference
of red-haired partner)
Fig. 14.7 Averageness as a result of evolution by “repro-
ductive success of the most attractive.” In this example,
red would be the most frequent color of hair (or nearly the
“average” color) after a few generations. This mechanism
tion. The human face and the human body plan
except for the internal organs are mirror symmetric. This is also true for most species of the animal kingdom. Radial symmetry is found, e.g., in
jellysh and starsh or in plants. In early animal
life, bilateral symmetry of the body plan was
probably advantageous for locomotion and was
genetically xed for the whole body plan at an
early stage of evolution. As a consequence, the
detection of bilaterally or radially symmetrical
structures was advantageous because it was a
reliable strategy to detect plants and animals in
the environment. This capability was necessary
New average face
would include genetically determined preferences in mate
choice as well as preferences by sociocultural
conventions
to nd predators, mates, or food. Visual perception of bilateral and radial symmetry was studied,
e.g., by Martinovic etal. [45] and Jennings and
Kingdom [46].
In addition, translational transformation invariance, i.e., periodic structures, may occur in sights
with regularly or irregularly repeating similar elements, like a host of owers, a shoal of sh, a site
with many mushrooms, or a tree full of fruit
(Fig.14.9). Regular translation in two dimensions
leads to characteristic areal patterns, e.g., sh
scales. Realizing scaling symmetry might have
been advantageous in pattern recognition and spa-
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