Onset of the adult reproductive capacity ANTH 230: From menarche to menopause PUBERTY Onset of the adult reproductive capacity

PEAK VELOCITY Changes in height AGE AT TAKEOFF

Changes in weight 10 11 12 13 14 15 16 Max weight velocity for boys ~ 45 lbs ~ 40 lbs Max weight velocity for boys Max weight velocity for girls 10 11 12 13 14 15 16 Age (yrs)

Growth in adolescence Tempo of growth during adolescence ANTH 230: From menarche to menopause Growth in adolescence Tempo of growth during adolescence Great variation between and within pops No correlation between timing of growth spurt and final stature Strong genetic control for tempo of growth

ANTH 230: From menarche to menopause This is a graphic illustration of what we just said.

Pubertal changes Females Breast Development Pubic Hair Growth Spurt ANTH 230: From menarche to menopause Pubertal changes Females Breast Development Pubic Hair Growth Spurt Hip broadening Menstruation Fat Deposition Development of “fecund” cycles

Tanner stages of development ANTH 230: From menarche to menopause Tanner stages of development

Socioecological context ANTH 230: From menarche to menopause Socioecological context Puberty Growth Maintenance Reproduction Maintenance ADULTHOOD CHILDHOOD

How can we explain the variation in age at puberty in girls?

Timing of puberty (or what determines the age at menarche) ANTH 230: From menarche to menopause Timing of puberty (or what determines the age at menarche) https://www.youtube.com/watch?v=RkjgQ91EV4w

Timing of puberty (or what determines the age at menarche) ANTH 230: From menarche to menopause Timing of puberty (or what determines the age at menarche) Genetic polymorphisms Environmental determinants Sociological Developmental Attachment Energy availability Evolutionary/life history EARLY DEVELOPMENT https://www.youtube.com/watch?v=RkjgQ91EV4w

What Regulates Age at Menarche? ANTH 230: From menarche to menopause What Regulates Age at Menarche? Heritability of age at menarche ~50% Frisch “Body Fat” Hypothesis Tanner/Ellison: “Pelvic Size” Hypothesis Energetics Stress-suppression Psychosocial acceleration Paternal investment Child development

What Regulates Age at Menarche? ANTH 230: From menarche to menopause What Regulates Age at Menarche? Heritability of age at menarche ~50% Frisch “Body Fat” Hypothesis Tanner/Ellison: “Pelvic Size” Hypothesis Energetics Stress-suppression Psychosocial acceleration Paternal investment Child development

Frisch “Body Fat” Hypothesis ANTH 230: From menarche to menopause Frisch “Body Fat” Hypothesis Accumulation of fat is critical for menarche A particular, minimum ratio of fat to lean mass is normally necessary for menarche (˜17% fat/body wt) and the maintenance of female reproductive ability (˜22% fat/body wt). 

Skeletal Maturation Hypothesis ANTH 230: From menarche to menopause Skeletal Maturation Hypothesis A girl must reach an appropriate age of skeletal development in order to reproduce

Skeletal Maturation Hypothesis ANTH 230: From menarche to menopause Skeletal Maturation Hypothesis A girl must reach an appropriate age of skeletal development in order to reproduce Pelvic dimensions are significantly correlated with menstrual age

Comparison of Hypotheses ANTH 230: From menarche to menopause Comparison of Hypotheses 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 Height accounts for 50% of the variance

Skeletal Growth and Age at Menarche Ellison

What’s the adaptive value? ANTH 230: From menarche to menopause What’s the adaptive value? Natural selection favored delaying menarche until pelvis can handle reproduction without complications

Secular Trend

What Regulates Age at Menarche? ANTH 230: From menarche to menopause What Regulates Age at Menarche? Heritability of age at menarche ~50% Frisch “Body Fat” Hypothesis Tanner/Ellison: “Pelvic Size” Hypothesis Energetics Stress-suppression Psychosocial acceleration Paternal investment Child development

Energetics hypotheses ANTH 230: From menarche to menopause Energetics hypotheses Energy availability during childhood Age at menarche

Stress-suppression hypothesis ANTH 230: From menarche to menopause Stress-suppression hypothesis Increase Age at menarche Social stressors during childhood

Psychosocial acceleration hypothesis ANTH 230: From menarche to menopause Psychosocial acceleration hypothesis Decrease Age at menarche Social stressors during childhood

Paternal investment hypothesis ANTH 230: From menarche to menopause Paternal investment hypothesis Father’s role during childhood Age at menarche

Child development hypothesis ANTH 230: From menarche to menopause Child development hypothesis Social development environment during childhood Age at menarche

Correlation does not mean causation

Hormonal, Anatomical and Developmental Correlates of Puberty ANTH 230: From menarche to menopause Hormonal, Anatomical and Developmental Correlates of Puberty

The physiology of puberty (and correlates of age at menarche) ANTH 230: From menarche to menopause The physiology of puberty (and correlates of age at menarche) Adrenarche Body composition Insulin sensitivity The somatotropic (growth hormone) axis Skeletal development The hypothalamic-pituitary- (HPO) ovarian axis

Insulin dynamics and puberty ANTH 230: From menarche to menopause Insulin dynamics and puberty Transient decrease in insulin sensitivity  higher insulin levels. Related to increases in Growth Hormone

The physiology of puberty (and correlates of age at menarche) ANTH 230: From menarche to menopause The physiology of puberty (and correlates of age at menarche) Adrenarche Body composition Insulin sensitivity The somatotropic (growth hormone) axis Skeletal development The hypothalamic-pituitary- (HPO) ovarian axis

ANTH 230: From menarche to menopause The somatotropic axis

The hypothalamic-pituitary-ovarian axis ANTH 230: From menarche to menopause The hypothalamic-pituitary-ovarian axis

ANTH 230: From menarche to menopause

Adolescent Subfecundity ANTH 230: From menarche to menopause Adolescent Subfecundity Between 55%-85% menstrual cycles during first 2 years are anovulatory

Adolescent Subfecundity ANTH 230: From menarche to menopause Adolescent Subfecundity Between 55%-85% menstrual cycles during first 2 years are anovulatory HOWEVER, Any individual cycle may be ovulatory!

Child, Bride, Mother By STEPHANIE SINCLAIR http://www.nytimes.com/interactive/2015/02/08/opinion/sunday/exposures-child-bride-mother-stephanie-sinclair.html?_r=3

ANTH 230: From menarche to menopause “The global north has established a relatively arbitrary year in which adulthood starts—usually 18 years old. We have demarcated vulnerability as it fits with our cultural norms and practices, and then apply that to the rest of the world as though this conceptualization is a given.” Nichols & Farias (2015) "Notes from the field: Humanitarian discourses, systemic erasures, and the production of victimhood in 'Child, Bride, Mother’” link here