Sarah Hrdy belongs to a new generation of primate-watchers who are filling in the blanks concerning the everyday behaviors of our nearest relatives. Hrdy, and many of her coworkers (as well as the better-known Jane Goodall and Alison Jolly), are female; and they bring to their scholarship a special interest in the role of females in primate groups. Here then is Hrdy's survey of the data, based on her own observations of langurs in India and the many reports that have accrued since the mid-sixties. Her essential point is that females, no less than males, are competitive, sexually active, and socially involved members of groups. In the course of 70 million years of evolution, the primates show wide diversity in structure and behavior, exhibiting ""every known social system, except polyandry (one female, several males)."" Monogamy is the rule among some prosimians, among marmosets and gibbons--in which case females enjoy high status and are physically similar to males. Females dominate among squirrel monkeys and ring-tailed lemurs. On the other hand, the female hamadryas baboon ""is probably the most wretched and least independent of any nonhuman primate."" The hamadryas female is not related to other females in the harem, which is dominated by a single male. In contrast, there is a strong sisterhood among gelada females in similarly structured baboon groups. The gelada females can and do unite to rally against the male. What does Hrdy make of all this variety? For one, she debunks both macho and feminist myths: female primates are not meek, weak sisters who owe their existence to the benevolent protection of males, nor are they sweet uncompetitive ladies who know no lust for power, or Amazons who can look back to some primordial matriarchal past. Such creatures never evolved, says Hrdy. instead, she believes that human female sexuality is rooted in nonhuman primate evolution where one can find present evidence for orgasm, for concealed ovulation, and for year-round sexual receptivity. She further believes that these aspects of sexuality have been adaptive--allowing females to compete for promising males, to manipulate male behavior, and to increase male investment in offspring; as well as increasing the primate's potential for passing on her genes. Thus Hrdy casts her theories along well-known sociobiological lines. She also favors the admittedly reductionist hypothesis of British primatologist Richard Wrangham that primate groups are structured in response to the quality and quantity of food available. ""Females arrange themselves in space and time,"" she says, ""to maximize food intake while minimizing competition for food from either individual females or from other groups of females."" (Males, in turn, arrange themselves so as to control these dispersed females.) Such a conclusion belies the complexity of behavior Hrdy has observed, and even her suggestion of consciousness and strategic thinking (as well as the recognition of individual personalities that might lead to nonsexist bonding friendships). So, while Hrdy displays a fine eye and a fine hand at gathering and reporting the data, one may hope that further studies will engender less stark and materialistic underpinnings for human behavior.