Line	In 1971 researchers hoping to predict earthquakes in
	the short term by identifying precursory phenomena
	(those that occur a few days before large quakes
	but not otherwise) turned their attention to changes
(5)	in seismic waves that had been detected prior to
	earthquakes. An explanation for such changes was
	offered by “dilatancy theory,” based on a well-known
	phenomenon observed in rocks in the laboratory:
	as stress builds, microfractures in rock close,
(10)	decreasing the rock’s volume. But as stress
	continues to increase, the rock begins to crack and
	expand in volume, allowing groundwater to seep in,
	weakening the rock. According to this theory, such
	effects could lead to several precursory phenomena in
(15)	the field, including a change in the velocity of seismic
	waves, and an increase in small, nearby tremors.
	Researchers initially reported success in identifying
	these possible precursors, but subsequent analyses
	of their data proved disheartening. Seismic waves
(20)	with unusual velocities were recorded before some
	earthquakes, but while the historical record confirms
	that most large earthquakes are preceded by minor
	tremors, these foreshocks indicate nothing about
	the magnitude of an impending quake and are
(25)	indistinguishable from other minor tremors that occur
	without large earthquakes.
	In the 1980s, some researchers turned their
	efforts from short-term to long-term prediction.
	Noting that earthquakes tend to occur repeatedly in
(30)	certain regions, Lindh and Baker attempted to identify
	patterns of recurrence, or earthquake cycles, on which
	to base predictions. In a study of earthquake-prone
	sites along the San Andreas Fault, they determined
	that quakes occurred at intervals of approximately 22
(35)	years near one site and concluded that there was a
	95 percent probability of an earthquake in that area
	by 1992. The earthquake did not occur within the time
	frame predicted, however.
	Evidence against the kind of regular
(40)	earthquake cycles that Lindh and Baker tried
	to establish has come from a relatively new
	field, paleoseismology. Paleoseismologists
	have unearthed and dated geological features
	such as fault scarps that were caused by
(45)	earthquakes thousands of years ago. They have
	determined that the average interval between ten
	earthquakes that took place at one site along the
	San Andreas Fault in the past two millennia was
	132 years, but individual intervals ranged greatly,
(50)	from 44 to 332 years.

The United States hospital industry is an unusual market in that nonprofit and for-profit producers exist simultaneously. Theoretical literature offers conflicting views on whether nonprofit hospitals are less financially efficient. Theory suggests that nonprofit hospitals are so much more interested in offering high-quality service than in making money that they frequently input more resources to provide the same output of service as for-profit hospitals. This priority might also often lead them to be less vigilant in streamlining their services--eliminating duplication between departments, for instance. Conversely, while profit motive is thought to encourage for-profit hospitals to attain efficient production, most theorists admit that obstacles to that efficiency remain. For-profit hospital managers, for example, generally work independently of hospital owners and thus may not always make maximum financial efficiency their highest priority. The literature also suggests that widespread adoption of third-party payment systems may eventually eliminate any such potential differences between the two kinds of hospitals.

The same literature offers similarly conflicting views of the efficiency of nonprofit hospitals from a social welfare perspective. Newhouse (1970) contends that nonprofit hospital managers unnecessarily expand the quality and quantity of hospital care beyond the actual needs of the community, while Weisbrod (1975) argues that nonprofit firms--hospitals included--contribute efficiently to community welfare by providing public services that might be inadequately provided by government alone.

Line	Conodonts, the spiky phosphatic remains (bones
	and teeth composed of calcium phosphate) of
	tiny marine animals that probably appeared about
	520 million years ago, were once among the most
(5)	controversial of fossils. Both the nature of the
	organism to which the remains belonged and the
	function of the remains were unknown. However,
	since the 1981 discovery of fossils preserving not
	just the phosphatic elements but also other remains
(10)	of the tiny soft-bodied animals (also called conodonts)
	that bore them, scientists’ reconstructions of the
	animals’ anatomy have had important implications
	for hypotheses concerning the development of the
	vertebrate skeleton.
(15)	The vertebrate skeleton had traditionally been
	regarded as a defensive development, champions of
	this view postulating that it was only with the much
	later evolution of jaws that vertebrates became
	predators. The first vertebrates, which were soft-
(20)	bodied, would have been easy prey for numerous
	invertebrate carnivores, especially if these early
	vertebrates were sedentary suspension feeders.
	Thus, traditionalists argued, these animals developed
	coverings of bony scales or plates, and teeth were
(25)	secondary features, adapted from the protective
	bony scales. Indeed, external skeletons of this
	type are common among the well-known fossils of
	ostracoderms, jawless vertebrates that existed from
	approximately 500 to 400 million years ago.
(30)	However, other paleontologists argued that many of
	the definitive characteristics of vertebrates, such as
	paired eyes and muscular and skeletal adaptations
	for active life, would not have evolved unless the
	first vertebrates were predatory. Teeth were more
(35)	primitive than external armor according to this view,
	and the earliest vertebrates were predators.
	The stiffening notochord along the back of the
	body, V-shaped muscle blocks along the sides,
	and posterior tail fins help to identify conodonts as
(40)	among the most primitive of vertebrates. The lack of
	any mineralized structures apart from the elements
	in the mouth indicates that conodonts were more
	primitive than the armored jawless fishes such as the
	ostracoderms. It now appears that the hard parts that
(45)	first evolved in the mouth of an animal improved its
	efficiency as a predator, and that aggression rather
	than protection was the driving force behind the origin
	of the vertebrate skeleton.