Hines finds it impossible to make distinctions between the terms “sex” and “gender,” hence their refreshing, non-political interchangeability in her new book. After examining hormonal and brain-based data, Hines concludes that science cannot yet inform us which differences are determined biologically, socially, and/or both.

Chapter 1 launches into a summary of sex differences in human behavior, cognition, and laterality. She defines the term “difference” as one that is found on the average for males and females. Where available, she refers to the magnitude of difference based on meta-analyses “d.” This statistic allows the reader to contextualize the fact that cognitive differences between males and females are relatively small (i.e., less than 1 SD), amounting to about 1/11th the size of height differences, for example. Secondly, Hines proceeds to clarify that broad labels such as visuospatial or verbal abilities obscure sex differences that manifest reliably only on very specific tasks such as 3-D mental rotation or verbal fluency, respectively. Chapter 2 outlines the biological determinants of internal and external genitalia. The role of chromosomes and gonadal hormones in normal and abnormal development of physical appearance relevant to sexual reproduction in humans is reviewed. Chapter 3 addresses sexual differentiation in reproductive behaviors derived from experimental manipulation of gonadal steroids in rats, with the caution that primates and humans show similar, but not identical biological influences. The author presents data demonstrating that masculinity and femininity are two separate dimensions of reproductive behaviors. The conclusion that “no hormone can be thought of as exclusively female or male” will surprise some. Chapter 4 enumerates sex differences in size and shape of rat brains, as well as provides interesting chronological developments in animal research over the past 50 years.

We must wait until chapter 10 for a less cohesive presentation of sex differences in the human brain. There we learn that some of the subcortical structures found to be sexually dimorphic in animal models have human analogues, but that the functional nature of those structures are either unclear or show no sexual variability! Hines concluded that “few data are available linking structural sex differences to functional sex differences” (p. 211). She opines that methodological variation may be the culprit for a lack of consistency across human studies. There is a brief section on imaging (i.e., PET, MRI and fMRI technology) to add excitement and complexity to the issues. A recurring theme of the book seems to be the unmasking of popularized schemas, outdated theories, and myths fossilized in textbooks without sufficient empirical support (i.e., testosterone causes aggression in adults, sex differences in cognition are dependent upon sexual variation in the lateralization of brain functions).

A major strength of the book is its virtual compendium of hormonal influences (i.e., androgens and estrogens) on animal and human behaviors displayed by males and females in prenatal, neonatal, and pubertal surges, during periodic hormonal fluctuations in adulthood, as a result of experimental manipulation, and disorders of nature. Large numbers of publications have been synthesized to answer certain questions. An extensive glossary helps those less technically fluent. The influence of gonadal hormones on human sexuality (e.g., sexual identity, orientation, and libido), play, aggression, parenting, and finally on cognition appears in chapters 5, 6, 7, 8, and 9, respectively. While gonadal hormones clearly influence sexual differentiation of the first four behaviors (at least in one sex), Hines thinks that cognition may be the exception to the rule. Many neuropsychologists will appreciate that double-blind, placebo controlled and randomized designs are rare in this field. All agree that rigorous methodology is essential to test cognitive theories postulating hormonally causative factors on cognition. For example, the enhanced functioning postulated for estrogen and progestin replacement in postmenopausal women based on the early literature, was not supported by a recent controlled study in women over the age of 65 who may be, in turn, at a higher risk of dementia (Shumaker et al., 2003)!

Hines remains open minded to all methods of study, appropriately critical of poorly designed publications or unreplicated findings, and includes a few key studies highlighting environmental/cultural influences on gender differences. She sees reason to continue research, while generously offering insightful hypotheses to test the biological influences on brain organization of sexually diverse development in humans. However, it is clear that Hines is not convinced that the extant body of hormonal and brain research has proven to have major causative effects on human cognition or brain organization. Any single-\.authored text contains the writer's perspective, and this seasoned expert is no exception.

The book is not intended to be exhaustive, but rather it provides a scholarly synthesis of Hines' interests over the past 25 years. It serves as an excellent text for senior undergrad or graduate level courses on this topic. The final chapter, “Engendering the Brain,” cautiously offers empirically supported advice for clinicians who counsel families on sex assignment of babies born with ambiguous internal or external genitalia. Hines also musters several thoughtful arguments and data sets challenging the notions that brain engendered differences in cognitive abilities explain the male predominance in occupations like science and engineering, that sex differences in promiscuity (i.e., number of partners) are hormonally determined, and that testosterone makes men aggressive or limits their ability to nurture. She does a good job convincing us that the answers will be more complex than our original theories.