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Abstract:
Evolutionary psychology suggests that a woman's sexual attractiveness is based on cues of health and repro-
ductive potential. In recent years, research has focused on the ratio of the width of the waist to the width of
the hips (the waist-to-hip ratio (WHR)). A low WHR (i.e. a curvaceous body) is believed to correspond to
the optimal fat distribution for high fertility, and so this shape should be highly attractive. In this paper we
present evidence that weight scaled for height (the body mass index (BMI)) is the primary determinant of
sexual attractiveness rather than WHR. BMI is also strongly linked to health and reproductive potential.
Furthermore, we show how covariation of apparent BMI and WHR in previous studies led to the overesti-
mation of the importance of WHR in the perception of female attractiveness. Finally, we show how visual
cues, such as the perimeter-area ratio (PAR), can provide an accurate and reliable index of an individual's
BMI and could be used by an observer to diĦerentiate between potential partners.
Excepts
Introduction:
Selection will favour those patterns of behaviour that can
solve the basic environmental problems that face an
individual. One of the most fundamental of these
problems is mate selection: how do we choose a partner?
It is important that we are sensitive to the physical cues
that honestly signal that one individual is more desirable
(i.e. fitter and with a better reproductive potential) than
another, and use them to choose the partner which is
most likely to enhance our chances of successful reproduc-
tion.
• • •
In women, two potentially critical cues are shape and
weight. As far as shape is concerned, research has focused
on the ratio of the width of the waist to the width of the
hips (the waist-to-hip ratio (WHR)). A low WHR (i.e. a
curvaceous body) is believed to correspond to the optimal
fat distribution for high fertility, and
so this shape should be highly attractive.
• • •
The studies suggest that the
optimal WHR for attractiveness is 0.7 (Singh 1993) and that
WHR is a more important predictor of attractiveness than
the apparent weight of the female figure.
Recently, we reported that weight scaled for height (i.e.
the body mass index (BMI), the units of which are
kg/metre-squared) may be a far more important factor than WHR
in determining the attractiveness of a female body. This result is consistent with another study
that showed that successful female fashion and glamour
models all fall within a narrow BMI range.
• • •
Here we address three questions central to this debate.
First, we investigate the relative importance of BMI and
WHR in the perception of female attractiveness. Second,
if BMI plays a role in the perception of attractiveness,
what visual cues can be used to give an accurate and reli-
able measure of an individual's BMI? Third, if BMI is
the principal cue to physical attractiveness rather than
WHR, why do our results differ from those of previous
studies.
• • •
Methods: 40 male undergraduate men rated color images of 50 women in frontal view.
• • •
Discussion:
These results suggest that BMI is the primary determi-
nant of the attractiveness of female bodies. It accounts for
more than 70% of the variance in our analyses, whereas
WHR accounts for little more than 2%. Furthermore, we
provide evidence of a plausible visual cue to BMI (PAR)
that provides an accurate visual proxy of BMI on which
judgements of mate selection could be based. We suggest
that the importance attributed to WHR in previous
studies is likely to be an artefact of covarying WHR with
apparent BMI. When both WHR and BMI are known for
images of real women, their effects can be estimated sepa-
rately, and BMI emerges as the most important factor.
• • •
Put
together, the evidence suggests that the balance between
the optimal BMI for health and fertility is struck at
around a value of 18 - 19, which, in this study, is also the
preferred BMI for attractiveness.
• • •
We therefore suggest that, although a WHR of
0.7 may represent the most fertile fat distribution for a
given BMI, women with the same WHR but diĦerent
BMIs can diĦer radically in health and reproductive
potential. This suggests that there may exist a hierarchy
of cues used to determine the attractiveness of a potential
partner. BMI may be used as a primary `screening
criterion' to select the most attractive (i.e. healthiest and
most fertile) women from a range of possible partners,
and then other secondary factors such as body shape,
including WHR, may be used to discriminate between
these attractive individuals.
• • •
In addition to BMI and WHR, there are other features
that may play a role in female physical attractiveness.
Perhaps the best known of these is the degree of
symmetry shown by a body.
• • •
This
result suggests that although symmetry is a significant
factor in determining physical attractiveness (excluding
faces) under some circumstances, it is a comparatively
subtle cue compared with BMI or even WHR.
• • •
For example, the most attractive
WHR is reported to be 0.7, a value with which our study
concurs. However, several studies have suggested that
women with a higher WHR (and higher levels of free
testosterone) are more likely to give birth to boys
. So it
may be that, in societies where male children are particularly valued, such higher WHR values may be more
attractive.
In conclusion, we can say that whether or not these
preferences arose from cultural bias or evolutionary pressure, they will still have consequences for fitness and
reproductive potential in mate selection, and a man who
bases his judgement on BMI will optimize his chances of
choosing a healthy and fertile partner.
• • •
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