Do pretty women inspire
men to discount the
future?
Margo Wilson
*
and Martin Daly
Department of Psychology, McMaster University, Hamilton,
Ontario L8S 4K1, Canada
*
Author for correspondence (wilson@mcmaster.ca).
Recd 22.10.03; Accptd 29.10.03; Published online 12.12.03
Organisms ‘discount the future’ when they value
imminent goods over future goods. Optimal dis-
counting varies: selection should favour allocations
of effort that effectively discount the future relatively
steeply in response to cues promising relatively good
returns on present efforts. However, research on
human discounting has hitherto focused on stable
individual differences rather than situational effects.
In two experiments, discounting was assessed on
the basis of choices between a smaller sum of money
tomorrow and a larger sum at a later date, both
before and after subjects rated the ‘appeal’ of 12
photographs. In experiment 1, men and women saw
either attractive or unattractive opposite-sex faces;
in experiment 2, participants saw more or less
appealing cars. As predicted, discounting increased
significantly in men who viewed attractive women,
but not in men who viewed unattractive women or
women who viewed men; viewing cars produced a
different pattern of results.
Keywords: future discounting; sex differences;
sexual selection; attractiveness
1. INTRODUCTION
Present goods are preferred over future goods, both
because deferred benefits may be lost altogether and
because earlier reproduction generally yields a higher
intrinsic rate of increase than later reproduction. The rate
at which future goods are devalued with delay indexes
‘impatience’ or ‘future discounting’. Optimal discounting
depends on how quickly expected future utility or fitness
declines. For example, the optimal discount rate varies
with extrinsic mortality risk (Williams 1957).
Facultative responses to cues predicting the future are
often effectively equivalent to adaptive adjustment of dis-
count rates. For example, worker bees assume more
dangerous foraging activities both as their wings wear and
in response to infections that reduce their expected life-
span (Woyciechowski & Kozlowski 1998). Response to
cues of rising mortality risk or temporal foreclosure may
also be manifest as thresholds change. For example,
female wasps (Leptopilina heterotoma) accept a wider range
of oviposition sites in response to such cues (Roitberg et
al. 1992, 1993), and male scorpionflies (Panorpa cognate)
court females of lower quality as the season progresses
(Engqvist & Sauer 2002).
For similar reasons, cues promising relatively good
returns on present efforts should inspire allocations of
Proc. R. Soc. Lond. B (Suppl.) 271, S177–S179 (2004) S177 2003 The Royal Society
DOI 10.1098/rsbl.2003.0134
effort that effectively discount the future relatively steeply.
If the availability of courtship-worthy targets inspires an
escalation of present mating effort, for example, this must
typically be achieved at the expense of future efforts. This
line of reasoning inspired the study reported here: will
stimuli chosen to induce a ‘mating opportunity mindset’
engender steeper discounting in a standard laboratory
measure of personal discount rates?
Human discounting is typically assessed by offering real
or hypothetical choices between different monetary sums
after different delays (e.g. Frederick et al. 2002). Such
research has not been greatly influenced by evolutionary
theories of life-history trade-offs. Instead, researchers usu-
ally compare discount rates between types of people, not
situations, implicitly treating ‘impatience’ as a relatively
stable personality attribute (but see Laibson 2001). For
example, heroin addicts have been found to have higher
discount rates than controls (Kirby et al. 1999). However,
even in this research, there is some evidence that discount
rates vary facultatively; for example, addicts’ discount
rates increase with delay since their last injection
(Giordano et al. 2002).
A sex difference in discounting is predictable. Because
men have always had some chance of gaining fitness from
short-term expenditures of mating effort, whereas success-
ful reproduction typically requires more prolonged par-
ental investment by women, men should have evolved to
discount the future more steeply than women, and sex dif-
ferences in age-specific mortality confirm this expectation
(e.g. Arias 2002). Men also have higher discount rates
than women in choices of monetary rewards (Kirby &
Marakovic 1996).
We hypothesized that inducing a ‘mating opportunity’
mindset by presenting pictures of attractive women would
raise men’s discount rates in a monetary choice task,
whereas men who viewed pictures of relatively unattractive
women would show no such effect. The predicted mindset
could make men more present-oriented in general or have
specific effects related to the fact that money itself can be
used in mating effort; in either case, cues suggesting an
elevated present utility of such effort should raise the value
of present money relative to that of future money. Women
might respond similarly to images of attractive men if, for
example, improving one’s appearance to attract desirable
men is achieved by resource expenditure, but because fit-
ness gains from mating effort increments have presumably
always been higher for men, we predicted that such a
response would be smaller or non-existent in women.
Finally, to assess whether discount rates might be elevated
by more general affective or acquisitive responses, rather
than by the specific induction of a mating effort mindset,
we ran a parallel experiment in which subjects viewed rela-
tively appealing versus unappealing consumer goods,
namely cars.
2. MATERIAL AND METHODS
Research participants were 96 male and 113 female undergrad-
uates (age: 19.45 ±2.25 years) who volunteered for a study of ‘prefer-
ences for things we like’ for introductory psychology course credit.
They were randomly divided into four experimental conditions
(n=23 to 29) within each experiment (‘faces’ or ‘cars’) in a 2 ×2
between-groups factorial design: [sex] ×[images pre-selected for
either high (‘hot’) or low (‘not’) appeal].
Participants were informed of the procedures to follow, and told
that they could win some money with a lucky throw of dice at the
end of the experiment, in which case they would receive one of their
choices, randomly selected, so they should make each choice as if it
