- Black hole formation
- Science in Context
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- UXL Encyclopedia of Science | Angus & Robertson
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Total Users Language eng. Publication Detroit, Mich. Edition Second edition. Isbn A-As -- v. At-Car -- v. Cat-Cy -- v. D-Em -- v. En-G -- v. H-Mar -- v. Mas-O -- v. P-Ra -- v. Natural selection: A natural process that results in the survival of individuals or groups best adapted to the conditions in which they must exist.
Historical background Up until the eighteenth century, scientists generally believed that every species was created separately and remained unchanged for centuries. A philosophy known as natural theology, which arose in the seventeenth century, argued that the elegant and often complex features of organisms were the products of a direct design by God. But during the eighteenth century, the scientific community began to take a closer look at the immense diversity the vast differences and interrelatedness of connections between living things.
The excavation of plant and animal fossils prompted a new view that life on Earth developed gradually and unevenly from simple to advanced organisms. Different species that live in different environments often exhibit similar characteristics.
Black hole formation
Before the Industrial Revolution in England in the late s, this moth was predominantly light in color. Light coloring afforded perfect camouflage for the moth from predatory birds, since it blended so well with the similarly colored lichen-covered tree trunks on which it rested.
Kettlewell observed that, as this environmental transformation occurred, a dark form of the moth became increasingly common, eventually making up more than 90 percent of the population of moths in the affected areas. In the unpolluted areas, however, the original light form of the moth remained common. The common plan of such features demanded an explanation, so researchers set out to explain this similarity of traits in unrelated organisms. One effort to explain adapted traits was proposed by French botanist Jean-Baptiste Lamarck — Members of each succeeding generation stretched their necks to attain leaves at a higher level, which led to the modern giraffe.
Science in Context
In it, Darwin discusses the adaptations of organisms as the product of natural selection. Natural selection implies that—when forced to compete for limited resources such as food—those organisms best adapted to their specific environment are most likely to survive, reproduce, and transmit their traits to offspring.
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A boojum tree in Mexico during the dry season. The plant has adapted to seasonal changes in precipitation by restricting leaf growth in the dry season. Exactly how specific adaptations arise, however, is far from solved. It is easy to imagine how natural selection might produce relatively simple adaptations such as camouflage: a rabbit that lives in regions covered by snow in winter is better protected from prey if it produces a white coat during the winter months. The difficulty arises in explaining the evolution of extremely complex adaptations, such as the vertebrate eye.
Invertebrates, animals lacking a backbone, have simple eyes that detect only changes in light and form only a poor image at A boojum tree in Mexico during the moist season. The plant has adapted to seasonal changes in precipitation by maintaining leaves only in the moist season. Vertebrates, animals with a backbone, detect changes in light and motion and can form detailed images. How did such a superb adaptation come about? Darwin suggested the answer lies in very gradual changes over many generations, in which each intermediate stage leading to a fully formed eye had some adaptive value.
All the parts making up a fully functioning eye could evolve independently in small steps, each one building on and interacting with earlier changes. Thus, even a partially developed eye could be quite advantageous—indeed, could mean the difference between life and death—for an ancient vertebrate. Examples of adaptation Physiological adaptation. People who visit or live at high altitudes undergo physiological changes adaptations to adjust to the low-oxygen environment. Travelers to these areas commonly experience hypoxia, a condition of low oxygen in the blood.
Over a longer period, as the body adjusts to the change in altitude, the heart output and ventilation rate return to normal levels, but the red blood cell count continues to climb.
The most famous of all high-altitude peoples are the Sherpas of Nepal, whose climbing feats offer a stunning example of evolved adaptation. Evolutionary adaptation. Some of the most interesting cases of adaptation occur when two species evolve together so that each benefits from the other. This mutual dependence can be seen between the ant Formica fusca and the larval not yet fully developed stage of the lycaenid butterfly Glaucopsyche lygdamus.
Ebook Uxl Encyclopedia Of Science (Vol. 2 At
In return, the ants defend the caterpillar against parasitic wasps and flies. The mutual adaptation of two species in this manner is known as coadaptation. Interactions between species are not always beneficial for both members, however. Heliconius butterflies scatter the pollen from the flowers of Passiflora vines, benefitting the plant. But female butterflies also lay single eggs on young Passiflora shoots, and the developing larva may eat the entire shoot, a definite cost to the plant.
As an apparent adaptive response, several Passiflora species produce new shoots featuring a small structure that closely resembles a Heliconius egg. This distinction has led researchers Stephen Jay Gould and Elisabeth Vrba to suggest the term exaptation to describe traits that were originally intended to perform different functions in an organism. It may have evolved for its improved heating properties and only by chance proved to be advantageous as camouflage. In some cases, therefore, the features we recognize as adaptive are really only secondary uses of traits that originally arose for other reasons.
It is estimated that up to 25 percent of the American population displays some form of addictive behavior. Chemical addictions Alcohol. Alcohol is a central nervous system depressant that reduces inhibitions and anxiety. A damaged liver loses its ability to detoxify the blood, which can result in permanent mental changes, organ failure, and death.
UXL Encyclopedia of Science | Angus & Robertson
The opiates: opium, morphine, and heroin. Opiates also called narcotics are addictive drugs derived from opium, a drug made from poppy juice. Opiate: Any derivative of opium, for example, morphine or heroin. Withdrawal: The act of giving up the use of a drug by an addict, usually accompanied by unpleasant symptoms. In moderate doses, they relieve pain, promote a sense of wellbeing, and induce sleep; excessive doses, however, can cause coma or convulsions.
Opiates include opium and its derivatives—morphine and heroin.
Opium, a drug derived from the poppy, has been known since ancient times for its pain-relieving qualities and its ability to induce sleep. From the s through the s, it was widely used in Western medicine to treat a variety of ailments and was highly effective in deadening the sensation of pain during surgery.
In China, addictive opium smoking was rampant by the late s, where opium dens flourished. Some artists and writers of the nineteenth century claimed that opium use intensified their creativity by reducing their inhibitions. Opium is grown around the world, and in some countries smoking the drug continues to be common, though it is outlawed except for medicinal purposes in most Western nations.
Preparations of opium, such as paregoric, are sometimes prescribed for diarrhea. Codeine, an opium derivative, is an ingredient in many pain-relieving medications and cough syrups. Morphine is the active ingredient in opium.
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Some doctors even taught their patients how inject themselves. Tragically, thousands of people worldwide became addicted to the drug. In , the Bayer corporation the maker of aspirin synthesized produced by chemical means heroin from morphine and marketed it as a remedy for morphine addiction. Heroin, however, proved to be even more addictive than morphine. Physical or mental pain is relieved, and the user enters a deeply relaxed state for a few hours.
The powder also can be inhaled for a milder effect. Cocaine is a white, crystalline powder produced from the leaves of the coca plant, a South American shrub. It is extremely and powerfully addictive—some people need only a single exposure for addiction to occur.
For centuries, South American Indians have chewed the coca leaves for their stimulating and exhilarating effect. Cocaine came into use as a local anesthetic in the late s because of its numbing properties. As a pain reliever and stimulant, it was a common ingredient in popular nonprescription medicines of the late s and early s.
By the end of the twentieth century, cocaine was used only occasionally in the medical field, sometimes as a local anesthetic for some kinds of surgery. Most cocaine now is purchased and used illegally. A solid crystalline form known as crack, the most potent form of cocaine, is also smoked. Unlike the opiates, which cause drowsiness, cocaine gives its users energy.
Caffeine is a stimulant found in coffee, tea, chocolate, and cola drinks. It has been part of the human diet for many centuries and is one of the most widely used central nervous system stimulants in the world. In recent years, researchers have raised questions about possible risks associated with high caffeine intake, but no definite conclusions have been reached about the harmfulness of moderate amounts.