WHY WERE TH E trajectories of all key developments shifted uggs clearance to later dates
     in the Americas than in Eurasia? Four groups of reasons suggest themselves: the later start, more limited suite of wild animals and plants available for domestication, greater barriers to diffusion, and possibly smaller or more isolated areas of dense human populations in the Americas than in Eurasia.
     As for Eurasia's head start, humans have ugg boots clearance occupied Eurasia for about a
     million years, far longer than they have lived in the Americas. According to
     the archaeological evidence discussed in Chapter 1, humans entered the
     Americas at Alaska only around 12,000 B.C., spread south of the Canadian ice
     sheets as Clovis hunters a few centuries before 11,000 B.C., and reached the
     southern tip of South America by nike jordan heels 10,000 B.C. Even if the dis-
     3 6 4 ' GUNS, GERMS , AND STEEL
     puted claims of older human occupation sites in the Americas prove valid, those postulated pre-Clovis inhabitants remained for unknown reasons very sparsely distributed and did not launch a Pleistocene proliferation of hunter-gatherer societies with expanding populations, technology, and art as in the nike jordan heels Old World. Food production was already arising in the Fertile Crescent only 1,500 years after the time when Clovisderived hunter-gatherers were just reaching southern South America. Several possible consequences of that Eurasian head start deserve consideration. First, could it have taken a long time after 11,000 B.C. for the Americas to fill up with jordan heels people? When one works out the likely numbers involved, one finds that this effect would make only a trivial contribution to the Americas' 5,000-year lag in food-producing villages. The calculations given in Chapter 1 tell us that even if a mere 100 pioneering Native' Americans had crossed the Canadian border into the lower United States jordan heels and increased at a rate of only 1 percent per year, they would have saturated the Americas with hunter-gatherers within 1,000 years. Spreading south at a mere one mile per month, those pioneers would have reached the southern tip of South America only 700 years after crossing the Canadian border. Those postulated rates of spread UGG Boots Clearance and of population increase are very low compared with actual known rates for peoples occupying previously uninhabited or sparsely inhabited lands. Hence the Americas were probably fully occupied by hunter-gatherers within a few centuries of the arrival of the first colonists.