Puberty

Puberty
Presentation lecture by:Dr. Penny Frohlich
Hormones & Puberty

* Hypothalamus stimulates pituitary gland
o growth hormone which causes growth spurt
o ovaries and testes release gonadotrophins (sex hormones)
+ males: testosterone
+ females: estrogen and progesterone

Hormones & Puberty
* hormones stimulate
o growth of primary sexual characteristics (genital)
o growth of secondary sexual characteristics (non-genital)
o precursors to adult sexuality

Sex Differences in Puberty

* Growth spurt begins
o 10.5 years in girls
o 12.5 years in boys
o girls taller than boys between ages 11-13 years
* full adult height
o 17 years old in girls
o 21 years old in boys

Sex Differences in Puberty
* Menarche: first menstrual cycle
o typically occurs by age 12-13
o initially may involve anovulatory, irregular cycles
* Spermarche: first ejaculation
o typically occurs by age 15
o initial period of sterility

Sex Differences in Puberty
* Puberty marks an increased incidence of internalizing disorders in girls compared to boys (Haward & Sanborn, 2002; Kessler, 2003)
* Due to hormones? Environmental variables? Pregnancy?
* Is depression adaptive? (Nesse, 2000)

Precocious and Delayed Puberty
* Girls who enter puberty early more likely to have teen pregnancy
* girls who have teen pregnancy, more likely to have daughters with teen pregnancy

Precocious and Delayed Puberty
* Vandenbergh Effect
o male present --> earlier onset of puberty
o females only --> later onset of puberty
o may be a way of regulating population density

Precocious and Delayed Puberty
* Stable species – unchanging predictable environments, live long lives in large populations, large bodied, lavish lots of parental attention on few offspring – reach puberty later
* Opportunistic species – unstable unpredictable ecosystems – conditions good, everyone begins mating or pollinating --> conditions favorable, reach puberty rapidly

Precocious and Delayed Puberty
* Absent Father Theory:
o girls abandoned by their father behave like females from opportunistic species and reach puberty earlier (Draper, Belsky, & Harpending).
o process may be caused by pheromones
* Strategies for reproductive success
1) early pubertal development, low investment in offspring
2) later pubertal development, high investment in offspring
* Evidence in support:
o females with absent father reached puberty earlier (Surbey, 1988, 1990)
o females with greater emotional distance from parents reached puberty earlier (Sternberg, 1988)
o females with greater stress in parental relationship reached puberty earlier
Correlation does not equal causation!!!
* Absent father predicts early puberty:
o stress tends to delay menarche
o postpuberty stress inhibits ovulation
* Absent father predicts early puberty
o absent father may lead to lower SES
o lower SES may lead to problems associated with early menarche
* Absent father predicts early puberty
o Wamala et al. (1997)
+ 300 Swedish women ages 30-65
+ examined reproductive history, weight, SES
+ Findings: SES and obesity associated with higher number of children and earlier menarche
* Absent father predicts early puberty
o when the father is absent, mother may have poorer prenatal care (diet, rest, etc)
o Koziel & Jankowska (2002)
+ 1060 Polish girls aged 13.5 to 14.5 years
+ collected BMI and weight data
+ Findings: BMI and birthweight affected onset of menarche

* Early puberty predicts absent father:
o Mother’s genetics predicts earlier puberty
o Girls with early puberty get attention from males earlier - more likely to get pregnant?
o Girls likely to inherit onset of puberty from mother
* Third variable predicts absent father and early puberty:
o variant of x-linked androgen receptor that:
+ predisposes father to unstable relationships
+ causes early puberty in female offspring who inherit
o Comings et al. (2002): significant association between this gene and the following characteristics:
+ aggression and impulsivity
+ increased number of sexual partners
+ sexual compulsivity
+ paternal divorce
+ father absence
+ early menarche in females

* Early puberty, early spermarche

Hormones & Puberty.ppt