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SPECULATIONS ON THE ORIGINS OF HUMAN SEXUAL BEHAVIOR
Leanna Wolfe, Ph.D.Institute for Advanced Study of Human
SexualityFebruary 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
NisaThe Story of Kung Woman
What’s Unique About Humans?Hidden OvulationExtended Childhoods
Human Infants are the least mature apes at birthYear Round Female Receptivity
Irrelevant of ovulationBonding
Serial Pair bondingPolygamy/Monogamy
Based on economic, social and cultural factors
Just So Stories…Adam and Eve
Mitochondrial EveEarly Emergence of Male Provisioning
Female and her InfantsOwen Lovejoy
Hidden Ovulation emerged to enable Pair BondingHelen Fisher
Mitochondrial EveNewsweek’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
Dikika Child
3.3 mya
•Babies Less Mature at Birth• Mothers Require more Provisioning• Cultural Learning Important for SurvivalAdvent of the Nuclear Family???
Human-Ape Origins
Distribution of Apes
The Sex Contract
Owen Lovejoy, Male PaleoanthropologistImmature 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 bondsSuccessful 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 Full Estrus Display
Bonobo Estrus Display Attracts
Attention!
Human Ovulation Displays…
Female Showing Lots of Skin
(possibly ovulating)
Ovulation Test Kit
Measures rise of Luteinizing Hormone, signally impending ovulation
Explanations for Hidden Ovulation
Helen FisherAnthropologist
Sarah Blaffer HrdyAnthropologist
Mate Guarding PairbondingLove
Confuse MalesPrevent InfanticideFemale Independence
Sexual DimorphismAs an Indicator of Polygyny
Differences in size between male and female were more pronounced amongst the Australopithecine than modern day humans.
Testicle SizeAs an Indicator of Non-monogamy
With their relatively large testicles male chimpanzees are well-equipped for intrauterine sperm wars
Humans also have relatively large testicles…
Y-Chromosome Distribution• Less diversity than X-chromosomes
• Reveals widespread long-lasting polygyny among human populations
Sperm CompetitionAn 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 CompetitionThree unique kinds of sperm (blocker, fighter
and egg penetrator) were distributed differently depending on the context of lovemaking.
Only Egg Penetrator Sperm could cause a pregnancy
Sperm from different males might compete
Reproductive StrategiesMale (re: MPI)
Cad (low investment)Lad/Pair Bonded Mate (high investment)
Female (discerning Mate Value)Monogamous MateSexy Son HypothesisPartible PaternityExtended 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
Christopher RyanResearch Psychologist
Primeval societies engaged in communal parenting, group sex and were oblivious to paternity
S.E. Ex – Socio Erotic Exchange
How Males Care About Paternity
Dogon Menstrual HutsContemporary DNA TestingChastity BeltsFemale 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 BusinessoPaternity
Irrelevant• Homosexualityo GG Rubbingo Penis
Fencing•Pedophilia•Disputes Resolved with Sex •Group Sexual Bonding
Serial Monogamy: Is it Natural?Lust
testosteroneAttraction
DopamineNorepinephrine
AttachmentOxytocinVasopressin
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?