MOTHER NATURE A History of Mothers, Infants, and Natural Selection. By Sarah Blaffer Hrdy. Illustrated. 723 pp. New York: Pantheon Books. $35.   ----------------------------------------------------------------------   Sarah Blaffer Hrdy relates how a reporter once asked Robert Trivers, the sociobiologist who coined the term ''parent-offspring conflict,'' to comment on her work. ''My own view,'' he replied, ''is that Sarah ought to devote more time and study and thought to raising a healthy daughter. That way misery won't keep traveling down the generations.'' Although Trivers, as a working parent, failed to heed his own advice, Hrdy was haunted by a ''nagging anxiety lest Trivers was right.''   Her insecurity was reinforced by research done by the psychologist John Bowlby on infant attachment, which implied that maternal deprivation had dire consequences. A noted biologist and anthropologist, as well as a parent, Hrdy was especially aware of the behavioral repercussions of inadequate mothering, but her demanding career required her to share the care of her offspring with others. It was this ambivalence, combined with her background in primatology, that prompted Hrdy (now an emeritus professor of anthropology at the University of California, Davis) to question some cherished assumptions about motherhood. After a gestation of more than 20 years, Hrdy has delivered her evolutionary analysis of maternity: ''Mother Nature: A History of Mothers, Infants, and Natural Selection.''   Full text: http://www.nytimes.com/books/00/01/23/reviews/000123.23magurrt.html First Chapter: http://www.nytimes.com/books/first/h/hrdy-mother.html