As a newspaper science writer, I receive mostly positive feedback from readers, with the exception of the occasional scolding by a creationist. I am not used to being ridiculed or scorned or publicly berated. But one day, an editor from a publishing house asked me to write a science book about the male sex. "We've had books about women by women, and books about men by men," he said, "but no books about men written by women."

Now I know why.

There's just no way to write a book about the opposite sex without getting people mad. Some accused me of being a man-hating shrew -- or, well, something worse than a shrew. Others said I was excusing bad male behavior and therefore hastening the disintegration of society.

I suspect some of the haters didn't actually read the book. They weren't taking issue with the parts that explained how the first males got here, and where the Y chromosome came from and how it's evolving, or even the R-rated parts about the evolution of sperm and male genitalia. But a book on males just wouldn't be complete without addressing male behavior -- and that includes the way males approach sex.

The critics seemed to think that because I was writing a science book about males, I was saying men were "hard-wired" to act the way they do, whether it was sleeping around or cheating or fighting with other males. But nature is not so simple -- robots might be hard-wired, but not complex animals like Eliot Spitzer and John Edwards.

To reach this conclusion, I interviewed biologists, anthropologists, geneticists, psychologists, ornithologists, primatologists, endocrinologists and a few regular guys trying to get dates.

That led me to several common motifs that do run through males all across the natural world -- motifs that came about through evolution and shaped both male physiology and behavior, from the robin's song to the buck's antlers, the elephant seal's tonnage to the politician's philandering.

Stripped down to its essentials, the universal defining quality of males is the creation of sperm. And the universal defining quality of sperm is that they're smaller than eggs. Because their sperm are relatively small, males usually make many more of them than their female counterparts make eggs.

In most sexual species, that sets up a special kind of competition among males for the chance to reproduce. In humans, for example, women can have a handful of children but men can in theory have hundreds. (The Guinness book lists the male record for fecundity as 888 children, but it's not backed up by DNA evidence.) And if some men have hundreds, others won't have any. But there are a whole slew of ways males deal with this.

Male gorillas and dogs fight it out for the chance to be alpha male and monopolize multiple females. Penguins and many other birds stick with their mates and help raise their offspring. Peacocks attract peahens with their looks.

In other species, male animals come in several varieties. Scientists who study orangutans have found that some adult males grow huge and aggressive -- embodying the typical alpha male. The other males never grow any bigger than the females, and instead of fighting over the chance to mate they sneak in and mate when the alpha males aren't paying attention. These so-called "sneakers" may go on this way indefinitely or, if one of the big males somehow dies or disappears, the sneaker male's hormones will trigger a huge growth spurt and he'll metamorphose into an alpha male.

In many species, sneakers look exactly like females -- so they can hang out with them all day long without getting into any trouble with the alpha male. Male sunfish come in large and small types and both get to mate, but take different approaches. An even more complicated species called the side-blotched lizard has three kinds of males.

Each type has a different color. There are orange lizards, which are bigger and act like alpha males. There are yellow ones that look just like females, probably to fool the alpha males. And then there are blue males, also small, whose strategy is to work together in pairs, one getting the female and the other playing the wing man. The blue wing men spend their time chasing away the yellow sneaker males.

It turns out the competition for sex among these three kinds of male lizards is like a game of rock-paper-scissors. The yellow males can triumph over the orange alphas by their sneaking. The blue males can triumph over the yellow sneakers through cooperation, but since they aren't in disguise like the yellows, blues tend to get beaten up by the orange lizards, who are bigger and meaner.

I also learned there's abundant homosexual behavior in male animals. Killer whales and manatees engage in gay trysts, while gay geese and ducks latch onto one another in devoted male-male partnerships. About 8 percent of domestic rams are gay -- a great source of frustration for sheep breeders.

There are many theories about the persistence of homosexuality in nature -- but one of the most interesting connects it to the power of diversity, which gives creatures the flexibility to adapt to different circumstances.

If sheep and orangutans, fish and lizards can show so much male diversity, surely human males must employ an even more complicated variety of approaches to life and sex. And that's exactly what we see. Some men desire nothing more than to raise a family with one lifelong partner.

Other men just want to have fun. One man I interviewed admitted to having sex with more than 200 women by the time he turned 40. But he was ready to change -- and hoped to find someone to inspire him to settle down. Others may start out devoted to one partner but then their circumstances change -- they get elected governor of some state -- and they start mating with other women, too. Others get a taste of power and use it to attract other men.

I liked males as a sex before I even considered writing this book. Now I've learned to appreciate the glorious diversity of the world's males -- human and otherwise. Surely males are every bit as complicated and intriguing as females.

I wish Americans weren't quite so touchy about the sexes. And so my next book will cover something much less likely to invite trouble -- the beginning of the universe or perhaps the search for planets outside the solar system.