The dry mountain ranges of the Western united states contain rocks dating back 440 to 510 million years, to the Ordovician period, and teeming with evidence of tropical marine life. This rock record provides clues about one of the most significant radiations (periods when existing life-forms gave rise to variations that would eventually) evolve into entirely new species) in the history of marine invertebrates. During this radiation the number of marine biological families increased greatly, and these families included species that would dominate the marine ecosystems of the area for the next 215 million years. Although the radiation spanned tens of millions of years, major changes in many species occurred during a geologically short time span within the radiation and, furthermore, appear to have occurred worldwide, suggesting that external events were major factors in the radiation. And , in fact, there is evidence of major ecological and geological changes during this period: the sea level dropped drastically and mountain ranges were formed, in this instance, rather than leading to large-scale extinctions, these kinds of environmental changes may have resulted in an enriched pattem of habitats and nutrients, which in turn gave rise to the Ordovician radiation, However, the actual relationship between these environmental factors and the diversification of life forms is not yet fully understood.

Line	In current historiography, the picture of a consistent,
	unequivocal decline in women’s status with the advent
	of capitalism and industrialization is giving way to an
	analysis that not only emphasizes both change (whether
(5)	improvement or decline) and continuity but also
	accounts for geographical and occupational variation.
	The history of women’s work in English farmhouse
	cheese making between 1800 and 1930 is a case in
	point. In her influential Women Workers and the Industrial
(10)	Revolution (1930), Pinchbeck argued that the agricultural
	revolution of the eighteenth and early nineteenth
	centuries, with its attendant specialization and enlarged
	scale of operation, curtailed women’s participation in
	the business of cheese production. Earlier, she
(15)	maintained, women had concerned themselves with
	feeding cows, rearing calves, and even selling the
	cheese in local markets and fairs. Pinchbeck thought
	that the advent of specialization meant that women’s
	work in cheese dairying was reduced simply to
(20)	processing the milk. “Dairymen” (a new social category)
	raised and fed cows and sold the cheese through
	factors, who were also men. With this narrowing of the
	scope of work, Pinchbeck believed, women lost
	business ability, independence, and initiative.
(25)	Though Pinchbeck portrayed precapitalist,
	preindustrial conditions as superior to what followed,
	recent scholarship has seriously questioned the notion
	of a golden age for women in precapitalist society. For
	example, scholars note that women’s control seldom
(30)	extended to the disposal of the proceeds of their
	work. In the case of cheese, the rise of factors may
	have compromised women’s ability to market cheese
	at fairs. But merely selling the cheese did not
	necessarily imply access to the money: Davidoff cites
(35)	the case of an Essex man who appropriated all but a
	fraction of the money from his wife’s cheese sales.
	By focusing on somewhat peripheral operations,
	moreover, Pinchbeck missed a substantial element
	of continuity in women’s participation: throughout the
(40)	period women did the central work of actually
	making cheese. Their persistence in English cheese
	dairying contrasts with women’s early disappearance
	from arable agriculture in southeast England and
	from American cheese dairying. Comparing these
(45)	three divergent developments yields some reasons
	for the differences among them. English cheese-
	making women worked in a setting in which cultural
	values, agricultural conditions, and the nature of
	their work combined to support their continued
(50)	participation. In the other cases, one or more of
	these elements was lacking.

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.

Line	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
(5)	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
(10)	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
(15)	must instead be adapted 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
(20)	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
(25)	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
(30)	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
(35)	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
(40)	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,
(45)	making it a crucial initiating event in human evolution.