1 Lecture 6: Puberty & Puberty Rituals Lecture 6: Puberty & Puberty Rituals • Menarche Menarche • What causes menarche? What causes menarche? > 1. Frisch 1. Frisch “ Fatness Fatness” hypothesis hypothesis > 2. Tanner/Ellison 2. Tanner/Ellison “Pelvic Pelvic Size Size” • Hormonal Changes with Hormonal Changes with menarche menarche • Sex differences in timing Sex differences in timing of puberty of puberty • Puberty Rituals Puberty Rituals Behavioral Biology of Women — 2007 Menarche Menarche What Triggers Menarche? What Triggers Menarche? • Frisch Frisch “Body Fat Body Fat” Hypothesis Hypothesis • Tanner/Ellison: Tanner/Ellison: “Pelvic Pelvic Size Size” Hypothesis Hypothesis Frisch Frisch “ Body Fat Body Fat” Hypothesis Hypothesis • Accumulation of Accumulation of weight or fat is critical weight or fat is critical for menarche for menarche Frisch Hypothesis Frisch Hypothesis - Version 1 Version 1 • Average weight at Average weight at menarche is 47 kg menarche is 47 kg • Thus, 47 kg is Thus, 47 kg is a critical a critical weight that triggers weight that triggers menarche menarche (Frisch & Revelle, 1970) • PROBLEM: Graph PROBLEM: Graph shows there is shows there is NO NO relationship! relationship! Frisch Hypothesis Frisch Hypothesis - Version Version 2 • Looked at weight for Looked at weight for height instead height instead (Frisch, Revelle & Cook 1970) • Found critical body Found critical body composition that composition that triggers menarche triggers menarche • PROBLEM: assumes PROBLEM: assumes Difference in body Difference in body composition is due to composition is due to FAT FAT
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•• Few girls reached Few girls reached menarche below 17% menarche below 17% body weight as fatbody weight as fat
(Frisch & McArthur 1974)
•• Said this was a Said this was a minimum threshold for minimum threshold for menarchemenarche
•• PROBLEM: No PROBLEM: No evidence of increase in evidence of increase in probability of reaching probability of reaching menarche after attain menarche after attain 17% body fat17% body fat
Pelvic Size HypothesisPelvic Size Hypothesis
•• A girl must reach an appropriate age of A girl must reach an appropriate age of
skeletal development in order to reproduceskeletal development in order to reproduce
Pelvic Size HypothesisPelvic Size Hypothesis
•• A girl must reach an appropriate A girl must reach an appropriate age of skeletal development in age of skeletal development in order to reproduceorder to reproduce
•• Pelvic dimensions are Pelvic dimensions are significantly correlated with significantly correlated with menstrual agemenstrual age
Pelvic Size HypothesisPelvic Size Hypothesis
•• A girl must reach an A girl must reach an appropriate age of skeletal appropriate age of skeletal development in order to development in order to reproducereproduce
•• Pelvic dimensions are Pelvic dimensions are significantly correlated with significantly correlated with menstrual agemenstrual age
•• A biA bi--iliac diameter (pelvic iliac diameter (pelvic breadth) of 24 centimeters breadth) of 24 centimeters seems to be a minimum seems to be a minimum thresholdthreshold
Comparison of HypothesesComparison of Hypotheses
•• Ellison studied data from 67 girls weighed Ellison studied data from 67 girls weighed
and measured twice a year from 8 to 18 yrs.and measured twice a year from 8 to 18 yrs.
Graph of Menarcheal age and Wt.Graph of Menarcheal age and Wt.
Ellison
•• Weight accounts for 18% of the variance inWeight accounts for 18% of the variance in
menarcheal menarcheal ageage
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Skeletal Growth and Age at MenarcheSkeletal Growth and Age at Menarche
Ellison•• Height accounts for 50% of the varianceHeight accounts for 50% of the variance Ellison
Comparison of HypothesesComparison of Hypotheses
•• CONCLUSION: Menarche occurs after CONCLUSION: Menarche occurs after
peak growth spurtpeak growth spurt
Comparison of HypothesesComparison of Hypotheses
•• Weight accounts for 18% of the variance inWeight accounts for 18% of the variance in
menarcheal menarcheal ageage
•• Height accounts for 50% of the varianceHeight accounts for 50% of the variance
•• Natural selection has delayed menarche Natural selection has delayed menarche
until pelvis can handle reproduction without until pelvis can handle reproduction without
complicationscomplications
•• Menarche occurs after peak growth spurtMenarche occurs after peak growth spurt
Why theWhy the Confusion?Confusion?
•• Fat IS important for female reproductionFat IS important for female reproduction
Why theWhy the Confusion?Confusion?
•• Fat IS important for female reproductionFat IS important for female reproduction
•• But, attaining an adequate SIZE comes firstBut, attaining an adequate SIZE comes first
Why theWhy the Confusion?Confusion?
•• Fat IS important for female reproductionFat IS important for female reproduction
•• But, attaining an adequate SIZE comes firstBut, attaining an adequate SIZE comes first
•• Attaining adequate ENERGY for Attaining adequate ENERGY for
reproduction comes nextreproduction comes next
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Hormonal and Hormonal and
Developmental ChangesDevelopmental Changes
AndrogensAndrogens
•• About age 8 adolescent growth spurt begins About age 8 adolescent growth spurt begins
through action of androgens and growth through action of androgens and growth
hormones. Originates in adrenal gland.hormones. Originates in adrenal gland.
AndrogensAndrogens
•• About age 8 adolescent growth spurt begins About age 8 adolescent growth spurt begins
through action of androgens and growth through action of androgens and growth
hormones. Originates in adrenal gland.hormones. Originates in adrenal gland.
•• Androgens from adrenal gland and ovary Androgens from adrenal gland and ovary
stimulate pubic andstimulate pubic and axillary axillary hair hair
developmentdevelopment
Estradiol Estradiol -- II
•• Increase in Increase in estradiol estradiol ~8~8--9 yrs starts development of 9 yrs starts development of
breasts, uterus, vagina, parts of pelvisbreasts, uterus, vagina, parts of pelvis
•• Pelvic remodelingPelvic remodeling finishesfinishes at the end of skeletal at the end of skeletal
maturationmaturation
Breast DevelopmentBreast Development Breast DevelopmentBreast Development
•• BreastBreast
developmentdevelopment
occurs firstoccurs first
•• Influence of Influence of
estradiol estradiol and and
prolactinprolactin (from (from
anterior pituitary)anterior pituitary)
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Estradiol Estradiol -- IIII
•• Eventually stimulates mineral deposition Eventually stimulates mineral deposition
resulting in ossification and fusion of resulting in ossification and fusion of
epiphysesepiphyses
Precocious PubertyPrecocious Puberty
•• Treatable Treatable
with estrogen with estrogen
antagonistantagonist
Delayed or Loss of PubertyDelayed or Loss of Puberty
•• Treatable Treatable
with with GnRHGnRH
Skeletal Development Skeletal Development -- OverallOverall