The Animal with the Weirdest Sex Life

Sept 26th, 2012

What is normal?

• Among Humans:– Men and women join in long-term pair relationships that

are recognized by others– Marriage is a sexual union an a partnership for raising

children– Couples live embedded in a society of other couples with

whom they cooperate economically and share access to communal territory

– Sex occurs in private– Ovulation is concealed– Menopause

Sexual Cannibalism

• Fish, spiders, mantises

Men

Sept 26th, 2012

Role of Natural Selection in Male/Female Differences

• Anatomical structures and instincts that promote survival and reproductive success tend to become genetically programmed by natural selection

• Natural selection favors both males and females that leave many offspring

Why Don’t Males Breastfeed?

• Both sexes of placental mammals have mammary glands – nonfunctional in most males

• In male dogs and primates, the gland forms ducts and nipples

• In male mice and rates, the mammary tissue is present but not visible

• 90% of mammal species – mothers raise offspring alone

• The other 10% include lions, wolves, humans, marmosets, gibbons

Why Don’t Males Breastfeed?

Why Don’t Males Breastfeed?

• 3 mammals- placentals, monotremes, and marsupials diverged 135 mya – all breastfeed – so common ancestor must have too

Why are pubescent girls larger than boys?

• Sexual dimorphism