*Sexual dimorphism
is the difference in body size between males and females of the same species
There appears to be marked dimorphism in all
australopithecine species.
In primates, dimorphism is associated
with male dominance; there are no dimorphic primate species with pair bonding, which is the basis for the human family organization.
types of primate groups
-Multimale / Multifemale
-Uni-male / Multifemale
-Uni-female / Multimale
-Fission-Fusion
-Monogamous
Sexual Selection:
differential reproduction due to competition and choice of mates
Selection is a two-way street
Sexual selection usually works in two ways, although in some cases we do see sex role reversals:
sexual selection slide
Described by Darwin in Descent of Man and Selection in Relation to Sex (1871)
Competition: INTRAsexual
Choice: INTERsexual
Most prominent in polygynous species where competition for females is highest
Sexual Dimorphism
polygynous
1 man married to several women
polygamous
having more than one spouse at a time
polyandrous
women married to more than one man
monogamous
marriage to 1 person
Male competition (intrasexual)
Males compete for access to females, the amount of time spent mating with females, and even whose sperm gets to fertilize her eggs.
Female choice (intersexual)
Females choose which males to mate with, how long to mate, and even whose sperm will fertilize her eggs. Some females can eject sperm from an undesirable mate.
primary sexual characteristics
refer to the reproductive systems themselves
males: testes and penis
females: uterus and ovaries
secondary sexual characteristics
refer to those features that indicate sexual maturity (ability to reproduce)
males: facial hair, increased muscle mass and ability to obtain erections
females: widening of hips, development of breasts and onset of menstruation
titi monkeys mate for life and sit with their tails entwined
thats cute af