A thorough, often riveting review of research on homosexuality and male-female differences. ``Amid the chaos of debate is the virtual certainty that the biological origins of sexual orientation will become known to us,'' writes journalist Burr, who penned a controversial 1993 article on the subject for the Atlantic Monthly. He has to be congratulated for providing a fine summary and preview of what is politically one of the hottest topics today. He does it by stressing the science, by using lengthy quotes from the investigators, and by asking questions that go beyond the disputes and data to tap the attitudes and philosophies of the scientists themselves. The recent furor dates to 1993, when National Cancer Institute investigator Dean Hamer reported that sexual orientation was at least in part due to maternal inheritance of a gene located on the X chromosome. But Burr and his corps of experts underscore that genes are not destiny and exhort all to bury forever the nature/nurture dichotomy. The X locus Hamer has found is a part of the biological picture, and to explore it, Burr treats the reader to a primer on fetal development, the role of androgens and estrogens in creating males from the ``default'' female pattern, and the influence of hormones on the brain. His concluding chapters touch on the heart of the political/social/ethical dilemmas--the guarantee that there will be not only tests for the sex-orientation gene (or genes) but micro- gene-chips that will tell you what could be in store for your potential offspring--with all the Brave New World scenarios that engenders. Burr ends with a brief commentary on the conflict between science and religion and the peculiar irony of the current debate, which finds conservatives plumping for homosexuality as an immoral ``lifestyle choice'' while liberals may say it's all in the genes. By this time the savvy reader--thanks to Burr's excellent exposition--can say, A pox on both their houses.