I suppose everybody wonders, eventually, how it was that some human tribes came to gain ascendancy over the others.

For instance, white Europeans enslaved black Africans, and all but exterminated American Indians and Australian aborigines. Just one area of the entire globe, and the Semitic people that lived there, gave birth to Zoroastrianism, Judaism, Christianity, and Islam.

One of the oldest unified nations is that of China. Yet Europe still isn't unified, despite the fact that it occupies something like a similar landmass.

Throughout the course of human history, historians have posed all sorts of explanations for these differences. The oldest explanation is racism. And some people still hold to that mean-spirited sloppiness of thought.

For the past several weeks I've been listening to a book on tape that offers another explanation. It's called "Guns, Germs and Steel." The author is Jared Diamond, an evolutionary biologist. Diamond's theory is that from just two factors, the creation and spread of civilizations can be explained.

Those factors are a little surprising. First, he asks, how many species of plants were able to be easily domesticated? He lists a hosts of characteristics that matter. The seeds have to be large. The plants have to grow relatively quickly. They have to offer enough food value to make the planting and tending of the plants competitive with hunting and gathering.

But Diamond does more than just ask the question. He then surveys all the available plants around the planet, and comes up with a surprisingly short list. Those plants - barley, wheat, and a handful of other key grains - were not evenly distributed. Where they were found, they were domesticated, sometimes more than once. Where they were not found, human society remained more "primitive."

The second factor is the availability of fairly large animal species that are also capable of being domesticated. Domesticated, by the way, is not the same as tamed. Elephants, for example, can be tamed. But they have not been domesticated - bred in captivity for various traits.

Like plants, not all animals are good candidates for the process. Animals need to have a host of distinct characteristics: herd animals work best, organized along one or two leaders. They need to grow fairly rapidly (again, to pay off the time it takes to feed them). We all know about the breeds that made it: sheep, cattle, horses, pigs, reindeer, dogs.

But what most of us don't know is all the animals that man has TRIED to domesticate, but couldn't: zebras, rhinoceroses, and many others. Again, where domestication was possible, it happened. Where it wasn't, it didn't.

Diamond makes plain that some human peoples had the good fortune to find themselves in areas where plants and animals had better genetic likelihood to be adapted to human needs. Where that happened - the Fertile Crescent, China, much of central Europe - human populations quickly grew, supported by the ability to feed them. Where that didn't happen - North America, Australia, many islands - populations tended to remain small.

From the concentration of people, grew other things: guns and steel, certainly, which offered competitive advantages against other population centers. But also, the "germs" (smallpox, for instance) that enabled the Spanish, Portuguese and English to wipe out so many American Indians without ever firing a shot.

I was fascinated to learn about the Americas, where Indian success with beans and corn was stymied by the sheer north-to-south length of the Americas. It was hard for the crops to jump over the ecological differences between regions. By contrast, Eur-Asia is wide, enabling food to spread across the same general growing season without further modification.

Not everyone will find the answers to their questions in this book. But I'll tell you this: there aren't that many books around that seek to tell the entire history of the human race in approximately 400 pages, and do it so clearly and succinctly.

At this point, we have something like 400,000 titles in our collection. In my judgment, "Guns, Germs, and Steel" is one of the top 10: an impeccably researched and reasoned exploration of some of the deepest questions our own species faces.