This book is in two parts: (1) A Polysexual, Polygendered World, and (2) A Wonderous Bestiary.
The first part of the book is an independent 262 page exposition of homosexual, bisexual and transgendered animal sexuality. If you want to know what the birds and the bees are doing when Jerry Falwell isn't looking, this is the place to find out. Don't expect to find traditional family values in these pages. What you will discover instead is that animals aren't doing it for Darwin, they are doing it for fun. There are amazingly detailed descriptions, pictures and illustrations here of animals having all kinds of sex (that will amaze you), and most of it isn't for procreation.
More interesting to me, though, is the speculation on the sexual origins of language and culture in chapter 2 and the devastating examination in chapter 3 of bigotry in the biological sciences in over two hundred years of observations of animal homosexuality. Begemihl shows, for example, that in science as in society, there's a presumption of heterosexuality. Field researchers have commonly assumed, with no independent verification, that whenever they see a pair of animals engaging in what appears to be sexual behavior they are observing a male-female pair. Conversely, whenever they observe a known same-sex pair engaging in behavior that would be classified as sexual between a male and female, they classify it in some other way. This protocol largely precludes the gathering of data about animal homosexuality even when it's being observed. In some cases, though, it resulted in published studies being repudiated as much as 20 years later when it was discovered that what was presumed to be heterosexual behavior in a population was really entirely homosexual. (It's an interesting fact that in some species heterosexuality has never been observed by scientists even when they go to great lengths to observe it over periods of many years.) Also, a lot of animal homosexuality that has been recognized as such has simply been excluded from the published reports. As a result, there is still widespread belief among scientists and the public that animal homosexuality is rare or nonexistent. People will believe otherwise after reading this book.
Chapter 4 looks at the attempts to explain away animal homosexuality and chapter 5 considers arguments on the other side that try to attach evolutionary value to homosexuality. Bagemihl rejects all the proposals on both sides, demonstrating the weakness of all the explanations and typically showing that they are plainly inconsistent with the evidence of animal behavior. Finally, he arrives at the question that the reader has been waiting for for almost 200 pages: "Why does same-sex activity persist--reappearing in species after species, generation after generation, individual after individual--when it is not 'useful'?" His answer is not to show that it is useful, but rather to treat the plain existence of homosexuality as a reductio ad absurdum argument against the biologists' assumption that only traits that contribute to reproduction will survive (i.e. are useful). In pursuing this line of thought Begemihl offers interesting descriptions of animals that are nonbreeders, animals that suppress reproduction, animals that segregate the sexes so that reproduction can't happen, animals that engage in birth control, and animals that engage in other nonreproductive behaviors. He also shows that a lot of the sex that actually occurs is not for reproduction, but apparently for pleasure. All of this he believes calls for a new conception of the natural biological world.
The last chapter describes some ideas for a new paradigm, which he calls Biological Exuberance and I must say that it is much less convincing than the rest of the book. It is interesting nonetheless. Much of the last chapter is a description of the myths about animals of native North Americans, the tribes of New Guinea, and indigenous Siberian people. When I started reading this chapter I began to wonder if I had accidentally picked up a different book, but in the end he makes a connection between the myths and biological reality. In fact, he shows that some of these myths contain more facts about animals than you can find in any scientific text. Some of the most bizarre of the myths turn out to be true. Bagemihl writes: "The animal world--right now, here on earth--is brimming with countless gender variations and shimmering sexual possibilities: entire lizard species that consist only of females who reproduce by virgin birth and also have sex with each other; or the multigendered society of the Ruff, with four distinct categories of male birds, some of whom court and mate with one another; or female Spotted Hyenas and Bears who copulate and give birth through their 'penile' clitorides, and male Greater Rheas who possess 'vaginal' phalluses (like females of their species) and raise young in two-father families; or the vibrant transsexualities of coral reef fish, and the dazzling intersexualities of gynandromorphs and chimeras. In their quest for 'post-modern' patterns of gender and sexuality, human beings are simply catching up with the species that have preceded us in evolving sexual and gender diversity--and the aboriginal cultures that have recognized this."
So where does it end? In mystery. "Our final resting spot--the concept of Biological Exuberance--lies somewhere along the trajectory defined by these three points (chaos, biodiversity, evolution), although its exact location remains strangely imprecise." "Nothing, in the end, has really been 'explained'--and rightly so, for it was 'sensible explanations' that ran aground in the first place."
That's not a very satisfactory answer to my mind, but the book is nonetheless a source of many interesting phenomena and ideas. I enjoyed it greatly. I expect most people who read this long book will do as I have done--read part one completely and then selectively read about some particular animals in part two. The second part is subtitled "Portraits of Homosexual, Bisexual, and Transgendered Wildlife". It is an encyclopedia of the queer sexuality of approximately 300 species of mammals and birds. An appendix contains a long list of reptiles, amphibians, fishes, insects, spiders and domesticated animals in which homosexuality has been observed.