They found that more recent residential development is not any more scattered than development was in 1976. Forty two per cent of land in the square kilometre surrounding the average residential development in 1976 was open space, compared with 43 per cent in 1992. "While a substantial amount of scattered residential development was built between 1976 and 1992, overall residential development did not become any more biased toward such sprawling areas."
The authors are quick to point out that any one household would have seen much change in the study period, but that "if we zoom out and look at the city from a distance, we see little change, at least in terms of the proportions of sprawling and compact development: the new city is just like an enlarged version of the old city."
Overall, Boston is less scattered than Atlanta, however recent development in Boston has been less compact than recent development in Atlanta. Miami, San Francisco and Los Angeles were the most compact major cities, while Pittsburgh and Atlanta were the most scattered.
The authors also investigated why some cities are more sprawling than others. They found that a city's climate, topography and access to groundwater account for 25 per cent of the nationwide variation. When the climate is temperate, people spread out to have more space to enjoy the weather.
Hilly places see more scattered development as people avoid the costs of building on hillsides — but mountains act as a barrier and lead to more compact development. Places with easy access to groundwater see more scattered development, since people can supply remote houses with water by drilling inexpensive wells rather than paying for water lines.
"The presence of aquifers is particularly important," says Turner, "and that seems to me to have policy implications. It looks as if controlling access to groundwater is an important way to control whether development spreads or not."
Roads, on the other hand, have no impact on the extent to which development is scattered, despite commonly held beliefs to the contrary. "We looked at a lot of measures of road density — miles of road per area, average distance to a road, distance to an interstate exit — and we could find no relation between those measures and the scatteredness of development," Turner says.
The number of municipalities in a metropolitan area also does not affect development patterns. "You hear about fragmentation of jurisdictions being an important determinant of development patterns and we could find no evidence for that," says Turner. However, the team also found that development near cities is less scattered if it occurs in a municipality than if it occurs in an unincorporated area of a county. This suggests that people may be moving out to just beyond municipal boundaries in order to avoid more stringent municipal regulations.
One of the common complaints about urban sprawl is that as development spreads, municipal services such as roads, sewers, police and fire protection are more expensive. The authors suggest that this concern is well founded. Development in municipalities that receive larger subsidies from higher levels of government is, on average, more scattered. Says Puga, "This suggests that as local taxpayers are held accountable for infrastructure costs, they respond by insisting on patterns of development that require less infrastructure spending."
"People have been eager to rush to policy prescriptions without a very good understanding of the underlying phenomena," says Turner. "We wanted to try to put the policy discussion on sounder footing."
Anthropologists once thought that the ancestors of modern humans began to walk upright because it freed their hands to use stone tools, which they had begun to make as the species evolved a brain of increased size and mental capacity. But discoveries of the three-million-year-old fossilized remains of our hominid ancestor Australopithecus have yielded substantial anatomical evidence that upright walking appeared prior to the dramatic enlargement of the brain and the development of stone tools.
Walking on two legs in an upright posture (bipedal locomotion) is a less efficient proposition than walking on all fours (quadrupedal locomotion) because several muscle groups that the quadruped uses for propulsion must instead to provide the biped with stability and control. The shape and configuration of various bones must likewise be modified to allow the muscles to perform these functions in upright walking. Reconstruction of the pelvis (hipbones) and femur (thighbone) of “Lucy”, a three-million-year-old skeleton that is the most complete fossilized skeleton from the australopithecine era, has shown that they are much more like the corresponding bones of the modern human than like those of the most closely related living primate, the quadrupedal chimpanzee. Lucy’s wide, shallow pelvis is actually better suited to bipedal walking than is the rounder, bowl-like pelvis of the modern human, which evolved to form the larger birth canal needed to accommodate the head of a large-brained human infant. By contrast, the head of Lucy’s baby could have been no larger than that of a baby chimpanzee.
If the small-brained australopithecines were not toolmakers, what evolutionary advantage did they gain by walking upright? One theory is that bipedality evolved in conjunction with the nuclear family: monogamous parents cooperating to care for their offspring. Walking upright permitted the father to use his hands to gather food and carry it to his mate from a distance, allowing the mother to devote more time and energy to nurturing and protecting their children. According to this view, the transition to bipedal walking may have occurred as long as ten million years ago, at the time of the earliest hominids, making it a crucial initiating event in human evolution.
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发表于 2009-1-17 03:50:00
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