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.

    Even more than mountainside slides of mud or snow, naturally occurring forest fires promote the survival of aspen trees. Aspens' need for fire may seem illogical since aspens are particularly vulnerable to fires; whereas the bark of most trees consists of dead cells, the aspen's bark is a living, functioning tissue that—along with the rest of the tree—succumbs quickly to fire.

    The explanation is that each aspen, while appearing to exist separately as a single tree, is in fact only the stem or shoot of a far larger organism. A group of thousands of aspens can actually constitute a single organism, called a clone, that shares an interconnected root system and a unique set of genes. Thus, when one aspen—a single stem—dies, the entire clone is affected. While alive, a stem sends hormones into the root system to suppress formation of further stems. But when the stem dies, its hormone signal also ceases. If a clone loses many stems simultaneously, the resulting hormonal imbalance triggers a huge increase in new, rapidly growing shoots that can outnumber the ones destroyed. An aspen grove needs to experience fire or some other disturbance regularly, or it will fail to regenerate and spread. Instead, coniferous trees will invade the aspen grove's borders and increasingly block out sunlight needed by the aspens.

    The fields of antebellum (pre-Civil War) political history and women's history use separate sources and focus on separate issues. Political historians, examining sources such as voting records, newspapers, and politicians' writings, focus on the emergence in the1840's of a new "American political nation," and since women were neither voters nor politicians, they receive little discussion. Women's historians, meanwhile, have shown little interest in the subject of party politics, instead drawing on personal papers, legal records such as wills, and records of female associations to illuminate women's domestic lives, their moral reform activities, and the emergence of the woman's rights movement.

    However, most historians have underestimated the extent and significance of women's political allegiance in the antebellum period. For example, in the presidential election campaigns of the 1840's, the Virginia Whig party strove to win the allegiance of Virginia's women by inviting them to rallies and speeches. According to Whig propaganda, women who turned out at the party's rallies gathered information that enabled them to mold party-loyal families, reminded men of moral values that transcended party loyalty, and conferred moral standing on the party. Virginia Democrats, in response, began to make similar appeals to women as well. By the mid-1850's the inclusion of women in the rituals of party politics had become common-place, and the ideology that justified such inclusion had been assimilated by the Democrats.

    Companies that must determine well in advance of the selling season how many unites of a new product to manufacture often underproduce products that sell well and have overstocks of others. The increased incidence in recent years of mismatches between production and demand seems ironic, since point-of-sale scanners have improved data on consumers' buying patterns and since flexible manufacturing has enabled companies to produce, cost-effectively, small quantities of goods. This type of manufacturing has greatly increased the number of new products introduced annually in the United States. However, frequent introductions of new products have two problematic side effects. For one, they reduce the average lifetime of products; more of them are neither at the beginning of their life (when prediction is difficult) or at the end of their life (when keeping inventory is expensive because the products will soon become obsolete). For another, as new products proliferate, demand is divided among a growing number of stock-keeping units (SKU's). Even though manufacturers and retailers can forecast aggregate demand with some certainty, forecasting accurately how that demand will be distributed among the many SKU's they sell is difficult. For example, a company may be able to estimate accurately the aggregate number of shoes it will sell, but it may be uncertain about which specific types of shoes will sell more than other types.