This document discusses how women's fertility cycles influence their mate preferences and how sexual selection has shaped human sexuality and relationships. It argues that at higher fertility phases in their cycle, women seek more genetically fit males through extra-pair flings. It also discusses how female orgasm and preferences for certain male physical traits function as mechanisms of cryptic female choice that have driven the evolution of these male traits over time. The document suggests modern lifestyles undermine natural fitness indicators that were important for sexual selection in our ancestral past.

1. Sexual Fitness and
Women’s Fertility Cycles
Geoffrey Miller

2. DNA: wonderful but fallible
for 3.5 billion years

3. DNA: wonderful but fallible
replication
• http://www.youtube.com/watch?v=4jt
mOZaIvS0

4. Sex evolved 1.2 billion years ago:
easier to spread good mutations,
purge bad mutations from offspring
Bacterial conjugation via pilus

5. Eyes evolved 543 m.y.a.  mate choice
 Cambrian explosion of biodiversity

6. Evolution =
natural selection for efficient survival +
social & sexual selection for conspicuous signals

7. Every primate face is a different set of
sexually-selected ornaments

8. Every primate face is a different set of
sexually-selected ornaments

9. Every primate face is a different set of
sexually-selected ornaments

10. Averaged female faces across Europe

11. Costly signaling principles
allow vast range of
innovative signals
 Conspicuous waste (size,
materials, energy, time)
 Conspicuous precision
(typicality, symmetry,
pattern repetition, fit, finish)
 Conspicuous creativity
(novelty, variety)
 Conspicuous reputation
(status, prestige, familiarity,
branding)

12. Physical fitness indicators
Morphological
Face
Height
Muscles
Fat Deposits
Health
Behavioral
Sports
Dance
Sex
Michael Jordan
Maria Sharapova

13. The human brain: a fitness-indicator
wonderfully vulnerable to mutations
Most of the genome is expressed in the brain;
Most harmful mutations disrupt brain function somewhat

14. Mental fitness indicators
Semi-practical,
Semi-ornamental
Intelligence
Language
Mental Health
Status
Wealth
Moral Virtues
Mostly
Ornamental
Creativity
Music
Art
Humor
Happiness

15. Pair-bonding & mutual mate
choice for over a million years
• Like socially
monogamous birds
• Mutual display of fitness
indicators
• Assortative mating for
mate value & status
• Yields sexual equality in
many indicators &
signaling motives

16. Women’s ovulatory cycles
Fertility
(probability of
pregnancy
given
copulation)
Days into cycle 

17. Women at higher fertility phase
seek to poach better genes:
• More mate search & socializing, less
eating & staying home
• Avoid rape & incest more effectively
• Less satisfied with long-term partner if
he’s lower fitness
• More fantasies, flirtation, dancing, &
short-term affairs with higher-fitness men
• Mate-guarded more closely by lowerfitness partners
• Hormonal contraception (the Pill)
eliminates all this

18. Women at higher fertility phase
show stronger preferences for
‘good genes’ traits in males
Physical fitness indicators
• Body height, muscularity
• Facial masculinity,
attractiveness
• Deep voice
• Healthy body scent
Mental fitness indicators
• Dominance & assertiveness
• Verbal & artistic creativity
• Good sense of humor

19. Women at higher fertility phase
are rated more attractive by men
•
•
•
•
•
• Earn higher tips per hour as
lap-dancers (Miller, Tybur, &
Jordan, 2007)
400
350
Dollars Earned Per shift
Skin condition
Facial attractiveness
Body shape
Body scent
Clothing more stylish &
revealing
• Voice pitch & timbre
• Verbal creativity
300
250
Normally Cycling
200
Pill Users
150
100
50
0
Menstrual
Fertile
Cycle Phase
Luteal

20. Cryptic female choice
• Co-evolution of male and female
genitalia and preferences
• Females evolve to favor male
traits for better copulatory
courtship, as indicators of genetic
quality and phenotypic condition:
– larger, more complex male genitalia
– longer, more vigorous copulation
– repeated ejaculations over time

21. Cryptic female choice favors more
complex male genitalia
Damselfly penis

23. Clitoral anatomy for
cryptic female choice
Complex deep structures, not
just the glans clitoris
• circle the vagina
• assess penis girth & length,
& copulatory vigor
• project to different cortical
areas (Komisaruk et al., 2011)

24. Female sexual pleasure
as a mate choice system
• Female orgasm should:
– differ across males & situations –
100% ‘reliable’ would be
indiscriminate
– promote repeated mating with
favored males – not necessarily
increase fertility from one-shot
copulation through ‘upsuck’
• Differential sexual pleasure should
predict partner choice regardless of
woman’s base rate of orgasm

25. Female preferences for
longer-than-average penis sizes;
aversion to small penises
•
•
•
•
•
•
•
•
Francken et al. (2002): Netherlands
Stulhofer (2006): Netherlands
Dixson et al. (2007a): China
Dixson et al. (2007b): Cameroon
Dixson et al. (2010): New Zealand & California
Brody & Weiss (2010): Czechoslovakia
Shaeer et al. (2012): Middle East
Costa, Miller, & Brody (2012): Scotland:
Women who prefer longer penises are more
likely to have vaginal orgasms (but not clitoral
orgasms)

26. Mautz, Wong, Peters, & Jennions
(2013) PNAS
• 105 Australian women rated attractiveness of life-sized
projected male bodies
• Higher shoulder-to-waist ratio strongly attractive
• Strong & equal effects of height and penis length

27. Erectile function as
a sensitive fitness indicator
Poor erectile function;
• is a sensitive early marker for cardiovascular
disease (Gazzaruso et al., 2011)
Good erectile function:
• predicts lower risk of heart attack, stroke,
diabetes (Jackson et al., 2010; Nehra et al.,
2012)
• reveals better physical fitness in men aged 1840 (Hsiao et al., 2012) and 40-75 (Agostini et al.,
2011)
• reveals lower oxidative stress & inflammation
(Meldrum et al., 2012)
• reveals aerobic capacity and exercise level
(Kratzik et al., 2009)
• is a general marker for male health (Salonia et
al., 2012)

28. Copulation as a risky activity
for low-fitness males
• Bohlen et al. (1984): copulation as
a low-energy activity, c. 3-5 METS
(like fast walking)?
• Cf. Levine et al. (2012): AHA
statement ‘Sexual activity and
cardiovascular disease’:
Copulation moderately increases
risk per minute of angina (‘coital
angina’), myocardial infarction
(heart attack), and sudden death
from ventricular arrhythmia

29. Distance running, persistence hunting,
aerobic warfare favor female choice for
prolonged high-wattage copulation?

30. Sexual coevolution between
female choice and male traits
Vaginal & deep clitoral orgasms favor
physical fitness indicators:
 Longer, thicker, smoother penis
 Prolonged, aerobic copulation
Superficial clitoral orgasms favor
mental fitness indicators:
 Mating intelligence, sexual
experience, kindness, patience
Extended sexuality across ovulatory
cycle favors general health indicators:
 Repeated copulations before
pregnancy is likely

31. Natural fitness indicators
under-valued in modern societies
Physical fitness indicators:
• Consumerism:
– a few pro athletes & movie stars
– mass sedentary obesity & sexual
dysfunction
• Paleo: functional fitness & sexual
fitness for all

32. Natural fitness indicators
under-valued in modern societies
Mental fitness indicators:
• Capitalism:
– 1% rich, educated careerists &
entertainers
– 99% service workers, media
addicts, & bored spouses
• Paleo: mating intelligence &
courtship abilities for all

34. Questions?