Book 1 Reading and Speaking (1108795), страница 7
Текст из файла (страница 7)
A team led by AdamBoyko, a researcher at Cornell's Carlos D. Bustamante Lab, sampled 318 village dogs in Africa (as well ashundreds of dogs from North America and Europe for comparison) and discovered that the high genetic diversity ofcanines there resembles that found in east Asia. "We found almost without exception they're descended fromdifferent ancestral populations," Boyko says of the village dogs sampled in Africa. That means they may have beenthere just as long as others had been in east Asia.Researchers have also yet to figure out when people first began raising dogs. The going theory is that dogswere domesticated somewhere between 15,000 and 40,000 years ago. But, Boyko explains, genetic testing hasnot gone deep enough to come up with a more refined date.
To try to track down some more clues, field crewshave fanned out around the globe this summer to test village dogs in Vietnam, New Guinea, Malaysia and otherlocations in Eurasia in order to get more data.Of course, scrappy village dogs aren't often the focus of heartfelt conservation efforts, and some even faceactive elimination programs. But these pups also have challenges from newly arrived European-descent dogs,which threaten to make a splash in the regional gene pool. "It is unclear the degree to which older populations willbe able to maintain their genetic identity and persist in the face of modernity," Boyko and his co-authors wrote inthe PNAS paper.
So time is of the essence in digging up a solid answer about doggie descent.Looking back into the pooch family tree will help researchers learn more not only about dogs, but aboutancient people, as well. A genetic map of dog domestication could reveal important information about humanmigration and trade routes. "We may be able to turn dogs into a genetic marker for what human populations weredoing," Boyko says. He adds that he and his colleagues also plan to "look for which regions of the genome wentunder selection earliest," and from that "we'll also learn what traits were selected for at that time." That knowledge,18along with a little help from archaeologists, may be able to uncover sniff out just why the dog was so special andbecame most likely the first domesticated species.
(From Scientific American Online, August 20, 2009)Text B. Gene Study Suggests Goats Got Around Through Early Human CommerceAt the dawn of human history, long migrations were not for weaklings. Early travelers, however, could counton a sturdy, reliable and self-propelling source of food during their trips, a French study has just revealed.Researchers from Joseph Fourier University in Grenoble and the Muse National d’Histoire Naturelle in Paris, incollaboration with scientists from the University of Geneva in Switzerland, discovered that our ancestors likely usedgoats as "walking larders" some 10,000 years ago. Their findings, which are published on today's issue of theProceedings of the National Academy of Sciences (PNAS), come from an analysis of DNA extracted from goatmitochondria -small organelles that work as cellular power plants.The short string of DNA contained in the mitochondria (mDNA) - which accounts for only a small fraction ofthe total cellular DNA - accumulates mutations at a relatively regular rate and so researchers can use variations inits genes to measure evolutionary changes.
The more differences two individuals or species show in the nucleotidecomposition of their mDNA, the more distantly related they are. Moreover, because mitochondria are only inheritedfrom mothers, the DNA is not subject to the gene shuffling that affects the rest of the genome after fertilization.Therefore mDNA points researchers to only one or a few common female ancestors from which differentpopulations originated.For their studies, Gordon Luikart from Grenoble University and his colleagues collected mDNA from morethan 400 wild and domesticated goats in Europe, Asia, Africa and the Middle East, representing 88 breedsdistributed across the Old World. Their results suggest that all of the world's 700 million domestic goats originatedfrom only three ancestors, which were domesticated at different times in different places during prehistory.
The firstgoats were probably domesticated about 10,000 year ago at the dawn of the Neolithic in a region of the MiddleEast known as the Fertile Crescent.Intriguingly, the genetic analysis showed that, unlike other domestic animals such as cattle, sheep and pigs,today's descendants of the first domesticated goats are rather evenly distributed in all continents of the Old World.This pattern suggests that goats followed humans in their early migrations. "Goats have been a highly mobilespecies, probably as small and portable units of human trade throughout history," researchers David MacHugh andDaniel G.
Bradley note in a commentary to the PNAS paper.Goats can live on little food in harsh climates and still provide a major source of meat, skin and fibers formillions of people in the developing world. Strange as it might seem, we should rightfully include those skinnyanimals in the short list of man's best friends. (From Scientific American Online, May 8, 2001)Exercise 3. Do you agree with the following statements? Why? Why not? Explain your answer.1. Studies of animal domestication may shed light on human origin, development and migrations.2. Scientists know exactly when and where different wild animals were domesticated.3.
Dogs were first domesticated in Africa.4. Genetic material from numerous breeds and populations of animals is used for investigation.5. Mitochondrial DNA is used to determine the origin of species.6. Goats were extremely useful for ancient people.7. Dogs and goats were domesticated in the same region.8. All modern goats originate from the same common ancestor.Exercise 4. Divide into two groups. Each group should read either Text A or Text B on domestication ofwild horses.
In pairs, share your information with your partner and discuss both texts to combine all thedetails, so you could answer the questions in Exercise 5.Text A. DNA Hints at Origins of Domestic HorsesBy Sarah GrahamThe last sighting of a wild horse population occurred in 1969 in Mongolia. A far more common sight is adomestic horse, whether on a farm or a racetrack. Now scientists have shed new light on how these magnificentbeasts came to be controlled by humans. According to a report published online this week by the Proceedings ofthe National Academy of Sciences, modern horses were domesticated from several distinct ancestral populations.And because horse domestication may have played a key role in the spread of some European languages, thefindings could further the study of language evolution.To track the trail of domestic horses, Thomas Jansen of Biopsytec Analytik in Rheinbach, Germany, and hiscolleagues sequenced DNA from 318 horses representing 25 different breeds.
Specifically, the team analyzedmitochondrial DNA (mtDNA), which is inherited from the mother, and compared the recent samples to previouslypublished DNA data from 334 other animals. The researchers identified 17 distinct types of mtDNA and calculatedthat at least 77 different wild mares must have been domesticated in order to account for today's domestic horses.Just how these animals were domesticated remains unclear, however. Because of the necessary diversity of themares, the team posits that several separate and geographically diverse populations participated in the process.One theory holds that domestication occurred independently at a number of locales. Alternatively, the procedure19may have slowly spread from a single starting point.
In that case, the authors write, "the knowledge and the initiallydomesticated horses themselves would have spread, with local mares incorporated en route, forming our regionalmtDNA clusters." (From Scientific American Online, July 16, 2002)Text B. Modern Horses Have Many OriginsBy Julia KarowAbout 6000 years ago, somewhere in the Eurasian grassland steppe, man started to capture and tame wildhorses--at least that's what remains from archaeological sites in Ukraine and Kazakhstan, tell scientists. Initially,people did not only use horses for transport, but also for food; at the time, dogs, cows, sheep and goats hadalready lived with humans for several thousand years.
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