The Decine And Fall of the Human Empire: Why Our Species Is on the Edge of Extinction, Gee - B

                   "Humanity will perish. The reason is because of its very success. Humanity has become so preeminent, so dominant, that it threatens the functioning of the ecosystem on which it and all other creatures depend. No other species in the history of  creation has ever posed such a threat." 

                    We are all descended from a population that at one point almost a millennium ago was reduced to no more than 1280 individuals, leaving us with limited genetic diversity, thus weakening us.  We suffer from a litany of illnesses occasioned by our domestication of animals and our reliance on a handful of foods. We are headed to extinction because of climate change that will make vast portions of the planet unlivable.  The 'Karenina Principle' says we will meet our doom in our own way.  

                     "Africa played host to many different species even as our own - Homo Sapiens - was emerging there, more than 300,000 years ago." Our knowledge of our ancestors comes from the physical evidence of their fossils, but the depth of our understanding comes from our modern ability to study their DNA. By analyzing mitochondrial DNA, we know that each and every one of us descended from one African woman who lived 200,000 years ago. As the human population grew, it slowly left Africa, traveled east all the way to Indonesia, and eventually by boat to Australia. Sapiens went north encroaching on the Neanderthals and by 40-50,000 years ago, eliminated them while absorbing some of their genes. We were the only hominin species left standing, and demographers believe that when a species succeeds in eliminating its competition, the only way left is down.

                   Approximately 10,000 years ago, mankind in the Fertile Crescent, and soon around the world, turned to farming, likely because their population growth mitigated against continuing to rely solely on hunting and gathering.  Some of the consequences of humanity turning to farming was a decrease in body size and the rise of malnutrition, tooth decay, bone deformation and infectious diseases. Diseases such as tuberculosis, plague, and influenza spread from animals to people, and then spread between people in close proximity to each other. Of course, the increase in the food supply led to increases in the population.  That said, we remain "remarkably pox ridden, worm-eaten, and lousy." 

                  Now, "for the first time in human history the human  population is on a pronounced downward trend." The species is not replacing itself, and by 2100 there will be 5 times as many octogenarians as today, and only half as many children under 5.  The future will be dominated by climate change featuring rising sea levels, and a hotter and more humid world. Major coastal cities wiil flood and millions will leave Africa for Eurasia. Humanity will likely disappear no longer than 10,000 years from now.

                   The only optimism that the author can offer is that we need to colonize space. As far-fetched as that conclusion is, the first three-fourths of this book are great.