Lecture 6: Puberty & Puberty Rituals
Menarche
• Menarche
• What causes menarche?
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1. Frisch “ Fatness”
Fatness”
hypothesis
2. Tanner/Ellison “Pelvic
Size”
Size”
• Hormonal Changes with
menarche
• Sex differences in timing
of puberty
• Puberty Rituals
Behavioral Biology of Women — 2007
What Triggers Menarche?
Frisch “Body Fat”
Fat” Hypothesis
• Accumulation of
• Frisch “Body Fat”
Fat”
weight or fat is critical
for menarche
Hypothesis
• Tanner/Ellison:
“Pelvic
Size”
Size” Hypothesis
Frisch Hypothesis - Version 1
Frisch Hypothesis - Version 2
• Looked at weight for
• Average weight at
height instead
menarche is 47 kg
• Found critical body
• Thus, 47 kg is a critical
composition that
triggers menarche
weight that triggers
menarche
• PROBLEM:
• PROBLEM:
Graph
shows there is NO
relationship!
assumes
Difference in body
composition is due to
FAT
(Frisch & Revelle, 1970)
(Frisch, Revelle & Cook 1970)
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Frisch Hypothesis - Version 3
• Few girls reached
menarche below 17%
body weight as fat
Pelvic Size Hypothesis
• A girl must reach an appropriate age of
skeletal development in order to reproduce
• Said this was a
minimum threshold for
menarche
• PROBLEM:
No
evidence of increase in
probability of reaching
menarche after attain
17% body fat
(Frisch & McArthur 1974)
Pelvic Size Hypothesis
• A girl must reach an appropriate
age of skeletal development in
order to reproduce
• Pelvic dimensions are
significantly correlated with
menstrual age
Pelvic Size Hypothesis
• A girl must reach an
appropriate age of skeletal
development in order to
reproduce
• Pelvic dimensions are
significantly correlated with
menstrual age
• A bibi-iliac diameter (pelvic
breadth) of 24 centimeters
seems to be a minimum
threshold
Comparison of Hypotheses
Graph of Menarcheal age and Wt.
• Ellison studied data from 67 girls weighed
and measured twice a year from 8 to 18 yrs.
• Weight accounts for 18% of the variance in
menarcheal age
Ellison
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Skeletal Growth and Age at Menarche
Comparison of Hypotheses
• CONCLUSION:
• Height accounts for 50% of the variance
Menarche occurs after
peak growth spurt
Ellison
Ellison
Comparison of Hypotheses
• Weight accounts for 18% of the variance in
menarcheal age
Why the Confusion?
• Fat IS important for female reproduction
• Height accounts for 50% of the variance
• Menarche occurs after peak growth spurt
• Natural selection has delayed menarche
until pelvis can handle reproduction without
complications
Why the Confusion?
Why the Confusion?
• Fat IS important for female reproduction
• But, attaining an adequate SIZE comes first
• Fat IS important for female reproduction
• But, attaining an adequate SIZE comes first
• Attaining adequate ENERGY for
reproduction comes next
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Androgens
Hormonal and
Developmental Changes
Androgens
• About age 8 adolescent growth spurt begins
through action of androgens and growth
hormones. Originates in adrenal gland.
Estradiol - I
• Increase in estradiol ~8~8-9 yrs starts development of
breasts, uterus, vagina, parts of pelvis
• About age 8 adolescent growth spurt begins
through action of androgens and growth
hormones. Originates in adrenal gland.
• Pelvic remodeling finishes at the end of skeletal
maturation
• Androgens from adrenal gland and ovary
stimulate pubic and axillary hair
development
Breast Development
Breast Development
• Breast
development
occurs first
• Influence of
estradiol and
prolactin (from
anterior pituitary)
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Estradiol - II
• Eventually stimulates mineral deposition
resulting in ossification and fusion of
epiphyses
Delayed or Loss of Puberty
• Treatable
with GnRH
Precocious Puberty
• Treatable
with estrogen
antagonist
Skeletal Development - Overall
• Androgens
(testosterone)
• Estradiol
Pubertal Development
Negative Feedback
• Growth Hormone from anterior pituitary
HYPOTHALAMUS
GnRH
ANTERIOR PITUITARY
FSH
OVARY
LH
Follicle
Estrogens
• During 3rd month in utero negative feedback starts
• As system matures more estrogen needed to turn system off
• Finally enough FSH released to stimulate follicle to develop
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Negative Feedback
Positive Feedback
HYPOTHALAMUS
GnRH
Gonadal Maturation: 3 Hypotheses
• Gonadostat
Hypothesis
ANTERIOR PITUITARY
FSH
OVARY
• Falling sensitivity
of hypothalamus to
negative feedback
of steroids
LH
Follicle
Estrogens
• Positive feedback starts in response to high estrogen
• Capacity to evoke LH Surge occurs late in pubertal process
Gonadal Maturation: 3 Hypotheses
Gonadal Maturation: 3 Hypotheses
• Pituitary Drive
• Gonadal Drive
Hypothesis
Hypothesis
• Pituitary produces
increasing FSH and
LH (gonadotropins
(gonadotropins))
in response to the
same GnRH
stimulus from
hypothalamus
Development of LH pulses
• PrePre-puberty:
• Changes in gonad
come first
• Increasing amounts
of steroid cause
hypothalamus to
lose sensitivity to
negative feedback
Adolescent Subfecundity
No
LH Pulses
• Early Puberty:
Production
of LH pulses begins,
especially at night
• Between 55%55%-85% menstrual cycles during
first 2 years are anovulatory
• Late Puberty:
Increasing
magnitude and frequency
of pulses, also during day
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Secular Trend
• HOWEVER, Any individual cycle may be ovulatory!
ovulatory!
Differences between males and females
Puberty
Stages of Puberty
Females
Males
• Breast Development
• Pubic Hair
• Growth Spurt
• Hip broadening
• Menstruation
• Fat Deposition
• Fully “fecund”
fecund” cycles
•
•
•
•
•
•
•
•
Testes enlargement &
sperm production
Pubic hair
Penis enlargement
Growth spurt
Axillary hair
Facial hair
Voice changes
Broadening of shoulders
“ filling out”
out”
Puberty Rituals
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Mondari of Sudan
Krobo and Shai of Ghana
Krobo and Shai of Ghana
Pokot Girls
Surma
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Surma
Mbuti
Western Puberty Rituals?
Puberty Rituals
• Signs of menarche
• Scarification
• Adornment
• Hair style changes
• Restricted access to men
• Seclusion
• Symbolic clothing
Next Time...
• Menstruation — why did it
evolve?
• Menstrual seclusion huts and
menstrual taboos
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