SPECULATIONS ON THE
ORIGINS OF HUMAN
SEXUAL BEHAVIOR
Leanna Wolfe, Ph.D.
Institute for Advanced Study of Human Sexuality
February 9, 2011
When the gods gave people sex, they gave
us a wonderful thing. Sex is food: just as
people cannot survive without eating,
hunger for sex can cause people to die
Nisa
The Story of Kung Woman
What’s Unique About Humans?
 Hidden Ovulation
 Extended Childhoods
 Human Infants are the least mature apes at birth
 Year Round Female Receptivity
 Irrelevant of ovulation
 Bonding
 Serial Pair bonding
 Polygamy/Monogamy

Based on economic, social and cultural factors
Just So Stories…
 Adam and Eve
 Mitochondrial Eve
 Early Emergence of Male Provisioning Female and her
Infants
 Owen Lovejoy
 Hidden Ovulation emerged to enable Pair Bonding
 Helen Fisher
Mitochondrial Eve
Newsweek’s most
popular cover ever
The discovery of a
relatively recent
emergence of Homo
sapiens (less than
200,000 years ago)
was lost at the thought
of there having been a
Real Eve…
Extended Childhoods
•Babies Less Mature at
Birth
• Mothers Require more
Provisioning
• Cultural Learning
Important for Survival
Dikika Child
3.3 mya
Advent of the Nuclear
Family???
Human-Ape Origins
Distribution of Apes
The Sex Contract
Owen Lovejoy, Male
Paleoanthropologist
Immature young caused
females and males to form long
term pair bonds in order to
facilitate care for the young
A Maasai Tribe Shares Meat
Ethnographic data from foraging
societies establishes that a
woman’s offspring will be well-fed
simply if she is part of a tribe in
which there is at least one good
hunter.
A Sex for Meat Exchange?
 Certainly, but no evidence that it took the form of
monogamous pair bonds
 Successful male hunters might have exchanged their
bounties with multiple females, ultimately accessing
sexual variety
 Females in the quest for as much meat as possible
might have gladly exchanged sex with multiple male
hunters
Bonobo Estrus Displays
Bonobo Estrus Display
Attracts Attention!
Bonobo Full Estrus
Display
Human Ovulation Displays…
Ovulation Test Kit
Measures
rise of
Luteinizing
Hormone,
signally
impending
ovulation
Female Showing Lots of
Skin
(possibly ovulating)
Explanations for Hidden Ovulation
Helen Fisher
Anthropologist
Mate Guarding
Pairbonding
Love
Sarah Blaffer Hrdy
Anthropologist
Confuse Males
Prevent Infanticide
Female Independence
Sexual Dimorphism
As an Indicator of Polygyny
Differences in size between male and female were more
pronounced amongst the Australopithecine than modern day
humans.
Testicle Size
As an Indicator of Non-monogamy
With their relatively
large testicles male
chimpanzees are wellequipped for
intrauterine sperm wars
Humans also have
relatively large
testicles…
Y-Chromosome Distribution
• Less diversity
than Xchromosomes
• Reveals
widespread
long-lasting
polygyny
among human
populations
Sperm Competition
 An indicator of polyandrous mating patterns
Biologists Robin Baker and Mark
Bellis observed that females that
engaged in extra-pair copulations
retained more of their lover’s
ejaculate (70%) following orgasm
than their spouse/home partner’s
(40%). Thus sperm competition
could easily foster high levels of
genetic diversity.
Sperm Competition
 Three unique kinds of sperm (blocker, fighter and egg
penetrator) were distributed differently depending on
the context of lovemaking.
Sperm from different
males might compete
Only Egg Penetrator Sperm
could cause a pregnancy
Reproductive Strategies
 Male (re: MPI)
 Cad (low investment)
 Lad/Pair Bonded Mate (high investment)
 Female (discerning Mate Value)
 Monogamous Mate
 Sexy Son Hypothesis
 Partible Paternity
 Extended Family/Tribe/Village/Community
Sexy Son Hypothesis
David Buss,
Evolutionary Psychologist
Females seek
testosteronated
hunks near
ovulation while
long term
bonding is
sought with
fatherly
resource
providers.
Humans are by Nature
Hypersexual and Promiscuous
S.E. Ex – Socio
Erotic Exchange
Primeval societies
engaged in communal
parenting, group sex
and were oblivious to
paternity
Christopher Ryan
Research Psychologist
How Males Care About Paternity
 Dogon Menstrual Huts
 Contemporary DNA Testing
 Chastity Belts
 Female Genital Mutilations (FGM)
 Post Nuptial Virginity Tests
Why Males Care…
 Fear of Being Cuckolded into Investing in Someone Else’s Genes
 Assured that Just Their Genes Go Into the Future
 Pass on Wealth/Resources/Legacy to Heirs
When Males Don’t Care
 When They Are Bonobos
 When the State/Community/Village is Responsible for Resources
 Exchanging Service/Resources for Sexual Access
Is Chimp Social Sexuality Natural?
•Visible Estrus
•Multi-Male
Multi-Female
Troops
•Social Sexual
Hierarchies
•Mother-Infant
Bonds
Is Bonobo Social Sexuality Natural?
• Females Rule the
Business
oPaternity
Irrelevant
• Homosexuality
o GG Rubbing
o Penis Fencing
•Pedophilia
•Disputes Resolved
with Sex
•Group Sexual
Bonding
Serial Monogamy: Is it Natural?
 Lust
 testosterone
 Attraction
 Dopamine
 Norepinephrine
 Attachment
 Oxytocin
 Vasopressin
 Detachment
Is Partible Paternity Natural?
• Multiple Fathers
•Cooperative Parenting
•Group Sex Rituals
•Communal Resources
Ache (Amazon) Children Sharing Food
Ache Children with one of their Fathers
•Fetal Growth Requires
Regular Inseminations
•Multiple Fathers’
Characteristics Inherited
Is it All in the Eye of the Beholder?