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?