If the back seat is loaded with sacks of wood, the range is extended to 400 kilometres (250 miles). Again, this is comparable to the range of an electric car if the passenger space is sacrificed for a larger battery, as is the case with the Tesla Roadster or the electric Mini Cooper. The difference is, of course, that John has to stop regularly to grab a sack of wood from the back seat and refill the tank.
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Human's technological ascent began in earnest in what is known as the Neolithic Period ("New Stone Age"). The invention of polished stone axes was a major advance that allowed forest clearance on a large scale to create farms. This use of polished stone axes increased greatly in the Neolithic, but were originally used in the preceding Mesolithic in some areas such as Ireland .  Agriculture fed larger populations, and the transition to sedentism allowed simultaneously raising more children, as infants no longer needed to be carried, as nomadic ones must. Additionally, children could contribute labor to the raising of crops more readily than they could to the hunter-gatherer economy.  
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