The book describes itself in the opening paragraphs of its preface. For example, "Beginning with a world population of two billion in 1930, we will reach seven billion late in 2011 (amounting to FIVE billion additional people in a single human lifetime), followed by still more billions (numbers eight and nine) on-track to arrive by 2041. As this book will show, the impending arrival of our 8th, 9th, and 10th billions by century's end (or even 15.8 billlion, if worldwide fertility averages just 1/2 child per woman higher than the U.N.'s most recent medium-fertility estimates), together with the levels of overpopulation and environmental impacts that we already exhibit, arguably comprise the most important data set in human history and *a continuation of our current demographic tidal wave may constitute the greatest single risk that our species has ever undertaken*."