The question of exactly what sex differences exist and whether they have a biological foundation has been one of our culture's favorite enduring discussions. It should. After a baby is born, a parent's first concern is for its physical health. The next concern is its sex. Only in the most modern societies does sex not virtually guarantee the type of future life a new human being will have. Even in modern societies, one's sex usually plays a large role in the path a life follows. Scientists have published thousands of papers on the subject, with the general conclusion being that men and women are mostly the same, whatever differences exist have been socialized, and what differences exist have to do with women bearing children and men being physically stronger. In Warriors and Worriers, psychologist Joyce Benenson presents a new theory of sex differences, based on thirty years of research with young children and primates around the world. Her innovative theory focuses on how men and women stay alive. Benenson draws on a fascinating array of studies and stories that explore the ways boys and men deter their enemies, while girls and women find assistants to aid them in coping with vulnerable children and elders. This produces two social worlds for each sex which sets humans apart from most other primate species. Human males form cooperative groups that compete against out-groups, while human females exclude other females in their quest to find mates, female family members to invest in their children, and keep their own hearts ticking. In the process, Benenson turns upside down the familiar wisdom that women are more sociable than men and that men are more competitive than women.