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LBB 3 Mens Bodies.ppt
LBB_3_Mens_Bodies.ppt
Showing 125-139 out of 148
LBB 3 Mens Bodies.ppt-Men’s Bodies LeVay, Baldwin ...
LBB_3_Mens_Bodies.ppt-Men’s Bodies LeVay, Baldwin & Baldwin,
LBB 3 Mens Bodies.ppt-Men’s Bodies ...
LBB_3_Mens_Bodies.ppt-Men’s Bodies LeVay, Baldwin & Baldwin,
Page 125
Male Reproductive
Behavior
Individual differences:
Early hypothesis: high sex drive
correlated with high testosterone
levels
However, that correlation is not very
high.
Alternative hypothesis: differences in
the target tissues
(hormone receptors,
transmitters)
Page 126
Figure 5.27
Individual differences in sex drive
Page 127
Male Reproductive
Behavior
In most mammals, copulation consists of
stereotyped behaviors
Humans engage in a variety of sexual
practices & positions during coitus
The mating patterns of nonhuman
primates are less stereotyped than
those of rodents, but more programmed
than those of humans
Exception: Bonobos have been observed
to engage in numerous sexual postures,
including the face-to-face position
Page 128
Bonobos: chimps closest
to humans
Page 129
Make love, not war
Page 130
Make love, not war
Page 131
Male Reproductive
Behavior
Reproductive behavior in most mammals
depends on steroid hormones
The effects of castration on men vary:
Some men: no loss of sexual capacities
Others: a decrease or total loss
Plasma T in human males change with age,
with a peak during the teens and 20s.
Page 132
Effects of castration in
men in one study
More than half stopped sex rapidly
25% decreased more slowly
10% no change
Age is a factor
Page 133
Figure 3.19
Testosterone cycles in a man
Page 134
Ejaculation Requires Coordination of Muscles and Glands
Estrogens are required for male fertility; they
help maintain bone density and terminate
growth of bones after puberty.
Progestins are metabolic precursors for
androgens and estrogens.
Page 135
Ejaculation Requires Coordination of Muscles and Glands
As in women’s bodies, a feedback loop
involving the pituitary, hypothalamus, and
testicles controls male hormone levels.
The same hormonal messengers—GnRH,
FSH, and LH—play similar roles.
The brain regulates testicular hormone
production, thus life experiences affect
hormone levels.
Page 136
Figure 3.20
A feedback loop controls male hormone levels
Page 137
Ejaculation Requires Coordination of Muscles and Glands
Testosterone is an anabolic hormone; it
promotes buildup of muscle and increases
the oxygen-carrying capacity of the blood.
Athletes of both sexes may use them to
enhance performance, but this has
significant health risks.
Page 138
Box 3.6
Steroids and Sports
Tammy
Thomas used a
designer
steroid, which
altered her
head and body.