Epidemiology: Very early on, when Europeans contacted the New World prior to 1500 or so, huge populations of Native Americans were found. Populations were so dense that some early explorers found it impossible to settle. A few decades later the population of Native Americans had decreased so significantly it became much easier to settle, for example the Pilgrims. During the time period between first contact and settlement by Europeans up to 95 percent of Native Americans were wiped out by diseases Europeans introduced to the New World. Diseases such as influenza, measles, and small pox, which Europeans were well adapted to, decimated the Native Americans. There are several reasons for this including no prior exposure to the diseases, genetics, and ecological history of the North American continent. The book goes in-depth into each of these areas to examine why Native Americans were affected so drastically.
Genetics: Several sections of the book are devoted to genetics of natives to the Americas. As mentioned before, the genetics of Native American immune systems is discussed and why this is partially responsible for susceptibility to disease. Genetics are also examined to determine lineages of how North America was originally settled by Asians. There is also a small section devoted to how a scientist is searching for descendants of an extinct people group by searching for there mitochondrial DNA in people alive today.
Botany and agriculture: The history of corn is examined, which is quite an enigma. Corn is one of the major contributions of the Americas to the rest of the world. Other foods such as tomatoes, beans, potatoes, peanuts, peppers and squash were also completely unheard of in the Old World prior to contact with the new world. It is odd to think of Africa without peanuts, Italy without corn or tomatoes, and norther Europe without potatoes. This was the case though prior to the 1500's.
Overall, the book also gives you a decent idea of how science works. While science obviously informs us about unknowns in the world, it also finds a lot more unknowns, questions and can often be inconclusive. So, while this book gives an excellent history of North America is also is a pretty good science book. Also on my reading list is Charles Mann's next book, "1493: Uncovering the New World Columbus Created."