The Animal with the Weirdest Sex Life Sept 26 th, 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 26 th, 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?

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