Always lively and perspicacious, this clever book seeks to solve a seemingly trivial puzzle: while historians have mustered a host of plausible explanations (weapons, diseases, horses, etc.) for why Europeans spread so thickly into North America, Australia, New Zealand and Argentina (the lands Crosby labels "Neo-Europes"), what could possibly explain why the dandelion did so as well? The question doesn't appear so innocuous when it is pointed out that not just the dandelion, but the European housefly, and feral pigs, and a horde of other weeds, pests, crops, diseases and livestock from Europe followed suit. Quite often these organisms, even the domesticated ones, raced ahead of European explorers themselves, rapidly proliferating into vast herds and stands that the settlers themselves could not fathom. Why was this so? Why didn't, say, Australian weeds, their seeds inadvertently shipped back to England, eventually carpet the meadows and fields of Europe? To answer this odd question, Professor Crosby begins his story with Pangaea--the great supercontinent that began to split apart about 200 million years ago into the continents we now have scattered about the globe. These "seams of Pangaea" then forced a radical divergence in the terrestrial flora and fauna of the planet, and set the stage for the equally radical convergence initiated when European mariners crossed these now mid-oceanic seams. Crosby details case after case in each category: weeds, pests, livestock, diseases and crops. He forcefully illustrates how sudden and overwhelming the ecosystem takeover was until the suspense is too much to bear. What is the answer? He drops clues every now and then, and the most explicit one is in the form of a quote that begins one of the final chapters: if weeds are to be defined as those organisms that thrive on the disturbances caused by humans, then humans themselves must be considered the primary weed of all. Here, then is the answer: all the opportunistic fellow-travelers of the European diaspora are exquisitely coadapted to the scale and pace of the continuous ecological disequilibrium characteristic of the Old World civilizations--and they, in turn, furthered and helped generate that very disequilibrium. Together--humans, horses, cattle, pigs, rats, clover, peaches, measles and, yes, dandelions--comprised a potent self-replicating system, dimly discerned by its contemporaries, that could not be stopped once it spilled across the seams of Pangaea.