why do we have menstruation?people.fas.harvard.edu/~anth1380/slides/lecture 7.pdf · 2 human...

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Lecture 7: Why do we Lecture 7: Why do we

menstruate? / Menstrual Taboosmenstruate? / Menstrual Taboos

•• Why do we have Why do we have menstruation?menstruation?

•• Menstrual SynchronyMenstrual Synchrony

•• Menstrual Taboos Menstrual Taboos

Behavioral Biology of Women 2007

Menstrual HutMenstrual Hut

Why do we have Why do we have

menstruation?menstruation?

Why do we have Menstruation?Why do we have Menstruation?

•• Cyclical growth and retreat of the Cyclical growth and retreat of the endometrium is universal in mammalsendometrium is universal in mammals

•• External loss of blood & tissue restricted to External loss of blood & tissue restricted to Old World PrimatesOld World Primates

•• HUMANS: Most copious menstrual blood HUMANS: Most copious menstrual blood lossloss

Why not just maintain the endometrium?Why not just maintain the endometrium?

Do all animals menstruate?Do all animals menstruate?

In which species is menstruation most pronounced?In which species is menstruation most pronounced?

Human EndometriumHuman Endometrium

•• Endometrial arterioles channel maternal Endometrial arterioles channel maternal blood to the placenta. In humans there is blood to the placenta. In humans there is one artery for each placental chamber.one artery for each placental chamber.


•• Endometrial arterioles channel maternal Endometrial arterioles channel maternal blood to the placenta. In humans there is blood to the placenta. In humans there is one artery for each placental chamber.one artery for each placental chamber.

Human EndometriumHuman Endometrium•• Endometrial arterioles channel maternal blood to Endometrial arterioles channel maternal blood to the placenta. In humans there is one artery for the placenta. In humans there is one artery for each placental chamber.each placental chamber.

•• These These ‘‘spiral arteriesspiral arteries’’ require more blood require more blood pressure, thus making more blood available to the pressure, thus making more blood available to the embryo after implantationembryo after implantation

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•• Without implantation the retreat of the Without implantation the retreat of the endometrium results in injury to the endometrium results in injury to the microvasculature and thus menstruationmicrovasculature and thus menstruation

Results 1b – Ecological condition

Energetics

Poland multiple regressions with ET Poland multiple regressions with ET

(w/ cycle day from end)(w/ cycle day from end)

rrpp

0.450.450.100.10Mean daily caloriesMean daily calories

0.460.460.100.10%fat%fat

0.460.460.090.09WeightWeight

0.450.450.100.10BMIBMI

0.610.610.010.01Reproductive ageReproductive age

0.600.600.010.01AgeAge

0.450.450.100.10MenarcheMenarche

US simple regressionsUS simple regressions

rrpp

--0.330.330.400.40Mean daily caloriesMean daily calories

0.520.520.160.16%fat%fat

0.640.640.040.04WeightWeight

0.610.610.080.08BMIBMI

0.060.060.890.89Reproductive ageReproductive age

0.200.200.610.61AgeAge

0.410.410.270.27MenarcheMenarche

7

8

9

10

11

12

13

45 55 65 75 85 95

weight (kg)

ET (mm)

Endometrial thickness and weight

r = 0.53, p = 0.03

Clancy and Bribiescas in revision

Results 2 – Summary

Estradiol, the endometrial

proliferation hormone, positively

correlates with endometrial

thickness in this Polish sample. Progesterone also positively

correlates with endometrial

thickness.

Progesterone, the endometrial

maintenance hormone, is

significantly lower in this Polish

sample.

Secretory Phase of EndometriumSecretory Phase of Endometrium

• Estradiol stimulates DNA synthesis and mitotic activity

• Mucosa doubles in thickness

• Tubular glands penetrate the stroma and become greatly enlarged

• Progesterone causes enlargement of stroma cells and the expression of genes that code for proteins important in implantation

Secretory Phase of EndometriumSecretory Phase of Endometrium

• Estrogen primed endometrium binds progesterone which stimulates the glands to secret a rich mixture of glycoprotein, sugars and amino acids.

• Decidual tissue contains lipids, carbohydrates, nucleic acids and proteins.

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Theories for the Evolution of Theories for the Evolution of

MenstruationMenstruation

Why do we have menstruation?Why do we have menstruation?

•• Pathogen Elimination Pathogen Elimination HypothesisHypothesis

•• Embryo Elimination Embryo Elimination HypothesisHypothesis

•• Energy Economy Energy Economy

HypothesisHypothesis

•• Consequence of Consequence of

Uterine EvolutionUterine Evolution

Functional/Adaptive

Explanations

Non-Adaptive

Consequences

““Pathogen ProtectionPathogen Protection”” HypothesisHypothesis

•• Menstruation evolved Menstruation evolved to protect the uterus to protect the uterus

from spermfrom sperm--borne borne

pathogenspathogens

Pathogen Protection HypothesisPathogen Protection Hypothesis

•• No decrease in pathogens after menstruationNo decrease in pathogens after menstruationProblems:


•• No decrease in pathogens after menstruationNo decrease in pathogens after menstruation•• Menstruation may exacerbate infectionMenstruation may exacerbate infection

Problems:

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•• No decrease in pathogens after menstruationNo decrease in pathogens after menstruation•• Menstruation may exacerbate infectionMenstruation may exacerbate infection•• Sexual activity often occurs when Sexual activity often occurs when menstruation is absent.menstruation is absent.

Problems:


•• Cervical mucous prevents sperm from Cervical mucous prevents sperm from entering uterus.entering uterus.

Problems:


•• No association in primates with number of No association in primates with number of mating partners.mating partners.

Problems:


•• No decrease in pathogens after menstruationNo decrease in pathogens after menstruation•• Menstruation may exacerbate infectionMenstruation may exacerbate infection•• Sexual activity often occurs when Sexual activity often occurs when menstruation is absent.menstruation is absent.

•• Cervical mucous prevents sperm from Cervical mucous prevents sperm from entering uterus.entering uterus.

•• No association in primates with number of No association in primates with number of mating partners.mating partners.

•• Why isnWhy isn’’t it more widespread?t it more widespread?

Problems:








Functional/Adaptive

Explanations

Non-Adaptive

Consequences

Energy Economy HypothesisEnergy Economy Hypothesis

•• Outer layer of endometrium too bulky to Outer layer of endometrium too bulky to reabsorbreabsorb

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•• Outer layer of endometrium too bulky to Outer layer of endometrium too bulky to absorbabsorb

•• More costly to maintain endometrium than More costly to maintain endometrium than to grow a new oneto grow a new one


•• Outer layer of endometrium too bulky to Outer layer of endometrium too bulky to absorbabsorb

•• More costly to maintain endometrium than More costly to maintain endometrium than to grow a new oneto grow a new one

•• Higher metabolic rate during luteal phase Higher metabolic rate during luteal phase (more food intake)(more food intake)


•• External bleeding as a side effect when too External bleeding as a side effect when too much blood for remuch blood for re--absorptionabsorption


External bleeding as a side effect when too External bleeding as a side effect when too

much blood for remuch blood for re--absorptionabsorption

•• Why canWhy can’’t secretory endometrium be t secretory endometrium be

suspended?suspended?

•• Why wait two weeksWhy wait two weeks








Functional/Adaptive

Explanations

Non-Adaptive

Consequences

Menstruation: NonMenstruation: Non--adaptive adaptive

Consequence of Uterine EvolutionConsequence of Uterine Evolution•• Increased permeability of blood vessels that Increased permeability of blood vessels that supply the endometriumsupply the endometrium

(Finn, 1994)

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Consequence of Uterine EvolutionConsequence of Uterine Evolution

•• Differentiation of endometrial wall occurs Differentiation of endometrial wall occurs during every cycle (in mice only after during every cycle (in mice only after

implantation)implantation)

(Finn, 1994, 1998)



•• Blastocyst embeds in wall of endometrium.Blastocyst embeds in wall of endometrium.

(Finn, 1994)



•• Necessary consequence of Necessary consequence of having invasive blastocysthaving invasive blastocyst

(Finn, 1994, 1998)

•• Menstruation as a consequence Menstruation as a consequence of terminal differentiationof terminal differentiation

•• However, progesterone levels However, progesterone levels

could be maintained.could be maintained.








Functional/Adaptive

Explanations

Non-Adaptive

Consequences

Embryo Elimination HypothesisEmbryo Elimination Hypothesis

•• High incidence of High incidence of early pregnancy loss early pregnancy loss

(30%(30%--78%)78%)

(Clarke, 1994)


•• High incidence of early High incidence of early pregnancy loss (30%pregnancy loss (30%--

78%)78%)

•• Menstruation evolved Menstruation evolved as a means to eliminate as a means to eliminate

defective embryos defective embryos

(Clarke, 1994)

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•• High incidence of early High incidence of early pregnancy loss (30%pregnancy loss (30%--

78%)78%)

•• Menstruation evolved Menstruation evolved as a means to eliminate as a means to eliminate

defective embryos defective embryos

•• High Investment in High Investment in each offspring, want to each offspring, want to

eliminate losses earlyeliminate losses early

(Clarke, 1994)


•• High incidence of early High incidence of early pregnancy loss (30%pregnancy loss (30%--78%)78%)

•• Menstruation evolved as a Menstruation evolved as a means to eliminate defective means to eliminate defective

embryos embryos

•• High Investment in each High Investment in each offspring, want to eliminate offspring, want to eliminate

losses earlylosses early

•• Mating throughout cycle leads Mating throughout cycle leads to increased probability of to increased probability of

conjugation at conjugation at ‘‘wrongwrong’’ time.time.(Clarke, 1994)


•• High incidence of early pregnancy loss (30%High incidence of early pregnancy loss (30%--78%)78%)

•• Menstruation evolved as a means to eliminate Menstruation evolved as a means to eliminate defective embryosdefective embryos

•• Why do failed embryos need to be removed?Why do failed embryos need to be removed?

•• Why not reabsorbWhy not reabsorb

•• High Investment in each offspring, want to High Investment in each offspring, want to eliminate losses earlyeliminate losses early

•• Mating throughout cycle leads to increased Mating throughout cycle leads to increased probability of conjugation at probability of conjugation at ‘‘wrongwrong’’ timetime

•• Seen in other speciesSeen in other species

•• No evidence of thisNo evidence of this (Clarke, 1994)

Menstrual Synchrony?Menstrual Synchrony?

(McClintock)

Menstrual SynchronyMenstrual Synchrony

•• Study criticized Study criticized statisticallystatistically

•• IsnIsn’’t consistently t consistently foundfound

•• Why would it Why would it evolve?evolve?

Menstrual Synchrony Menstrual Synchrony

(Ellison)

•• Found on village levelFound on village level•• Not found in mothers/daughters or coNot found in mothers/daughters or co--wiveswives

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Menstrual Menstrual

TaboosTaboos

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What do Menstrual What do Menstrual

Taboos/Practices commonly Taboos/Practices commonly

involve?involve?

Early European Menstrual HutEarly European Menstrual Hut

Menstrual Taboos in NepalMenstrual Taboos in Nepal Wampanoag Menstrual HutWampanoag Menstrual Hut

1010

Hawaiian Menstrual HutHawaiian Menstrual Hut Menstrual TaboosMenstrual Taboos

Beng of Ivory CoastBeng of Ivory Coast

•• Women cannot go into Women cannot go into forestforest

•• Cannot work in field, chop Cannot work in field, chop wood, or fetch waterwood, or fetch water

•• Cannot cook for men Cannot cook for men •• Cannot touch another Cannot touch another womanwoman’’s fires fire

Menstrual TaboosMenstrual Taboos

Turkish VillageTurkish Village

•• Cannot perform Cannot perform religious ritualsreligious rituals

•• No intercourseNo intercourse•• Cannot participate in Cannot participate in the fast during the fast during

RamadanRamadan

•• Cannot make breadCannot make bread


Yurok Women (California)Yurok Women (California)

•• Menstruating women Menstruating women contaminate: water, food, contaminate: water, food,

houses, hunting gear, houses, hunting gear,

canoes, weapons, trailscanoes, weapons, trails

•• Cannot perform tasks that Cannot perform tasks that involves thoseinvolves those

What do Menstrual What do Menstrual

Taboos/Practices commonly Taboos/Practices commonly

involve?involve?


•• Sexual intercourse prohibitedSexual intercourse prohibited

(Strassman, 1992 from Murdock & White, 1969)

1111

Menstrual TaboosMenstrual Taboos•• Sexual intercourse prohibitedSexual intercourse prohibited

•• Husband and wife sleep apartHusband and wife sleep apart




•• Cannot cook for menCannot cook for men



•• Exclusion of women from sacred places/ritesExclusion of women from sacred places/rites

(Strassman, 1992 from Murdock & White, 1969)Balinese Temple


•• Change in activity patterns Change in activity patterns —— cancan’’t perform t perform

certain laborscertain labors


Menstrual TaboosMenstrual Taboos•• Prohibited from touching male items (hunting)Prohibited from touching male items (hunting)


Menstrual TaboosMenstrual Taboos•• Seclusion Seclusion —— menstrual hutsmenstrual huts


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Menstrual TaboosMenstrual Taboos•• Food & hygiene restrictions/ritualsFood & hygiene restrictions/rituals

•• CanCan’’t touch oneself t touch oneself —— use use scratcherscratcher




•• Cannot cook for menCannot cook for men

•• Exclusion of women from sacred places/ritesExclusion of women from sacred places/rites

•• Change in activity patterns Change in activity patterns —— cancan’’t perform t perform

certain labors certain labors

•• Prohibited from touching male items (hunting)Prohibited from touching male items (hunting)

•• Seclusion Seclusion —— menstrual hutsmenstrual huts

•• Food & hygiene restrictions/ritualsFood & hygiene restrictions/rituals

•• Special dress or adornmentSpecial dress or adornment(Strassman, 1992 from Murdock & White, 1969)


•• Special dress or adornmentSpecial dress or adornment


••E.g. painting face redE.g. painting face red

••Red hip cord (Red hip cord (Timbira Timbira of South America)of South America)Why are menstrual taboos so Why are menstrual taboos so

common?common?

Explanations of Menstrual TaboosExplanations of Menstrual Taboos

•• Menotoxins Menotoxins -- bacterial contaminantsbacterial contaminants

>> Idea that menstrual blood exposes a man to Idea that menstrual blood exposes a man to

““urethritisurethritis--causingcausing”” bacteria which is harmful bacteria which is harmful

to living tissues.to living tissues.

Functional Hypotheses



>> Idea that menstrual blood exposes a man to Idea that menstrual blood exposes a man to

““urethritisurethritis--causingcausing”” bacteria which is harmful bacteria which is harmful

to living tissues.to living tissues.

>>No evidence of such No evidence of such ‘‘menotoxinsmenotoxins’’

>>Little cyclical variation in vaginal bacterial Little cyclical variation in vaginal bacterial

floraflora

>>DoesnDoesn’’t explain why women isolated from t explain why women isolated from

fields, sacred area, weapons, etc.fields, sacred area, weapons, etc.


1313



•• HuntingHunting--preventing menstrual odor interferencepreventing menstrual odor interference




•• HuntingHunting--preventing menstrual odor interferencepreventing menstrual odor interference

>> Found in nonFound in non--hunting societieshunting societies

>> Women not involved in hunting in most Women not involved in hunting in most

societies anywaysocieties anyway

>> Lack of evidence of menstrual Lack of evidence of menstrual ““odorodor””

contamination with casual contactcontamination with casual contact



•• Castration Anxiety: Menstrual taboos reflect male Castration Anxiety: Menstrual taboos reflect male

‘‘castration anxietycastration anxiety’’ which is provoked by genital which is provoked by genital

bleedingbleeding

Cultural/Psychological Hypotheses


•• Castration Anxiety: Menstrual taboos reflect male Castration Anxiety: Menstrual taboos reflect male

‘‘castration anxietycastration anxiety’’ which is provoked by genital which is provoked by genital

bleedingbleeding

>> Contend that there is a correlation between Contend that there is a correlation between

castrationcastration--anxiety and menstrual taboosanxiety and menstrual taboos

>> Paige & Paige (1981) found no correlationPaige & Paige (1981) found no correlation



•• Castration AnxietyCastration Anxiety

•• Male DominanceMale Dominance

>> Menstrual taboos associated with male Menstrual taboos associated with male

dominance,dominance, patrilineal patrilineal descent,descent, patrilocal patrilocal

residenceresidence





>> Menstrual taboos associated with male Menstrual taboos associated with male

dominance,dominance, patrilineal patrilineal descent,descent, patrilocal patrilocal

residenceresidence

>>Strassman Strassman (1992) found no association.(1992) found no association.

>>More common in matrilineal or bilateral More common in matrilineal or bilateral

descent societies (that are normally less male descent societies (that are normally less male

dominated)dominated)


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•• Dilemma of WifeDilemma of Wife’’s Fecunditys Fecundity

>> Husband sends wife to menstrual hut as a signal Husband sends wife to menstrual hut as a signal

that hethat he’’s not interested in her fecunditys not interested in her fecundity

>> Gesture to make her available to adulterersGesture to make her available to adulterers

>> Increased solidarity of husbandIncreased solidarity of husband’’s political s political

powerpower





•• Dilemma of WifeDilemma of Wife’’s Fecundity (Paige & Paige)s Fecundity (Paige & Paige)

>> Sends wife to menstrual hut as a signal that heSends wife to menstrual hut as a signal that he’’s not s not

interested in her fecundityinterested in her fecundity

>> Gesture to make her available to adulterersGesture to make her available to adulterers

>> Increased solidarity of husbandIncreased solidarity of husband’’s political powers political power


•• However:However:

>> Women canWomen can’’t get pregnant during menstruationt get pregnant during menstruation

>> Disinterest in fecundity isnDisinterest in fecundity isn’’t supported t supported

ethnographicallyethnographically





•• Social Control Social Control -- Coercing people to respect social Coercing people to respect social

controlscontrols

>> Assert male superiorityAssert male superiority

>> Separation of male and female spheresSeparation of male and female spheres

>> Attack a rivalAttack a rival

>> Lay claim to a special relationLay claim to a special relation


>>DisprovenDisproven

>>No evidence developed for this purposeNo evidence developed for this purpose





•• Social ControlSocial Control

•• Inducement to HuntInducement to Hunt

>> Women go on Women go on ‘‘sex strikesex strike’’ during menstruationduring menstruation

>> Induces men to hunt meat for themInduces men to hunt meat for them


>>No No evidenceevidence

The The DogonDogonDogon - Menstrual Huts

1515


•• AntiAnti--cuckoldrycuckoldry

Adaptive/Evolutionary Hypotheses

0

2

4

6

8

10

12

14

16

18

Number of Women

0-1 2-3 4-5 6-7 8-9 10-11 12-13

Number of Menses in 2 Yrs

Number of Menses among Number of Menses among DogonDogon

AntiAnti--Cuckoldry HypothesisCuckoldry Hypothesis

•• Reveals womanReveals woman’’s menstrual status to her mates menstrual status to her mate

•• Used by men to protect against cuckoldryUsed by men to protect against cuckoldry

•• Makes paternity deception difficultMakes paternity deception difficult


•• Menstrual taboos were a reliable sign of Menstrual taboos were a reliable sign of

menstruationmenstruation

•• Publicized female reproductive statusPublicized female reproductive status

Tests among the Dogon

AntiAnti--Cuckoldry HypothesisCuckoldry Hypothesis

•• Reveals womanReveals woman’’s menstrual status to her mates menstrual status to her mate

•• Used by men to protect against cuckoldryUsed by men to protect against cuckoldry

•• Makes paternity deception difficultMakes paternity deception difficult


•• Why would this be in the womanWhy would this be in the woman’’s interest?s interest?

Problems:

•• Do you really need a menstrual taboo to signal Do you really need a menstrual taboo to signal

menstruation to your mate?menstruation to your mate?

Energy Balance HypothesisEnergy Balance Hypothesis

•• Menstrual taboos almost always involve a Menstrual taboos almost always involve a

decrease in womendecrease in women’’s workloads workload


Knott

1616

Sample of Behavioral Changes during MenstruationSample of Behavioral Changes during Menstruation

????Less strenuous Less strenuous

laborslabors

NoneNoneRungusRungus

NoNoCannotCannot cook cook

for familyfor familyCanCan’’t draw t draw

water or prepare water or prepare

foodfood

CanCan’’t enter t enter

family family

compoundcompound

DogonDogon

NoNoCannot Cannot

cook, cook,

prepare prepare

food,food,

Cannot gather Cannot gather

water or water or

firewoodfirewood

Cannot touch Cannot touch

weapons or weapons or

huntinghunting geargear

YurokYurok

NoNoCannot bake Cannot bake

breadbread

Cannot fastCannot fastCannot perform Cannot perform

religious ritualsreligious ritualsTurkeyTurkey

??Cannot cook Cannot cook

for menfor men

Cannot work in Cannot work in

field, chopfield, chop woodwood

Cannot touch Cannot touch

another another

womanwoman’’s fires fire

BengBeng

Intercourse?Intercourse?CookingCookingEnergyEnergyTaboosTaboos


Rungus Rungus of Borneoof Borneo

•• No No ‘‘taboostaboos’’

•• But But …… performs less performs less strenuous tasks.strenuous tasks.


Beng Beng of Ivory Coastof Ivory CoastEarly European Menstrual HutEarly European Menstrual Hut

Menstrual Taboos in NepalMenstrual Taboos in Nepal

What happens physiologically What happens physiologically

when you decrease your energy when you decrease your energy

expenditure?expenditure?

1717


•• Menstrual taboos almost always involve a Menstrual taboos almost always involve a

decrease in womendecrease in women’’s workloads workload


Knott

•• Decrease in activity levels and workload have a Decrease in activity levels and workload have a

positive effect on the probability of conception!positive effect on the probability of conception!

Exercise with Weight Loss and Exercise with Weight Loss and

Weight MaintenanceWeight Maintenance

•• Lower hormonal functioning in women in negative Lower hormonal functioning in women in negative energy balance.energy balance.

(Bullen, et al. 1985)

0

10

20

30

40

50

60

70

80

90

Irregular

Cycles

Delayed

Menses

Loss of LH

surge

Weight Maintenance Weight Loss

What happens if cycling women What happens if cycling women

spend one week a month resting spend one week a month resting

versus working?versus working?

Increased Probability of Increased Probability of Conception inConception in Next Cycle!Next Cycle!


•• Menstrual taboos almost always (or always) Menstrual taboos almost always (or always)

involve a decrease in womeninvolve a decrease in women’’s workloads workload


Knott

•• Decrease in activity levels and Decrease in activity levels and

workload have a positive effect on the workload have a positive effect on the

probability of conceptionprobability of conception

•• Thus, these practices may ultimately Thus, these practices may ultimately

increase the probability of conception increase the probability of conception

by decreasing energy expenditure and by decreasing energy expenditure and

thus may serve an thus may serve an adapative adapative functionfunction

Menstrual Menstrual

TaboosTaboos

1818


•• AntiAnti--Cuckoldry HypothesisCuckoldry Hypothesis

•• Energy Balance HypothesisEnergy Balance Hypothesis

•• Menotoxins Menotoxins -- bacterial contaminants bacterial contaminants

•• Hunting Hunting -- menstrual odor interferencemenstrual odor interference





•• Social ControlSocial Control

•• Inducement to huntInducement to hunt



Next Time...Next Time...

•• Reproductive EcologyReproductive Ecology

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