Архитектура Аудит Военная наука Иностранные языки Медицина Металлургия Метрология
Образование Политология Производство Психология Стандартизация Технологии
Text B. Gene Study Suggests Goats Got Around Through Early Human Commerce
At the dawn of human history, long migrations were not for weaklings. Early travelers, however, could count on 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, in collaboration with scientists from the University of Geneva in Switzerland, discovered that our ancestors likely used goats as "walking larders" some 10,000 years ago. Their findings, which are published on today's issue of the Proceedings of the National Academy of Sciences (PNAS), come from an analysis of DNA extracted from goat mitochondria -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 of the total cellular DNA - accumulates mutations at a relatively regular rate and so researchers can use variations in its genes to measure evolutionary changes. The more differences two individuals or species show in the nucleotide composition of their mDNA, the more distantly related they are. Moreover, because mitochondria are only inherited from 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 different populations originated.
For their studies, Gordon Luikart from Grenoble University and his colleagues collected mDNA from more than 400 wild and domesticated goats in Europe, Asia, Africa and the Middle East, representing 88 breeds distributed across the Old World. Their results suggest that all of the world's 700 million domestic goats originated from only three ancestors, which were domesticated at different times in different places during prehistory. The first goats were probably domesticated about 10,000 year ago at the dawn of the Neolithic in a region of the Middle East 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 mobile species, probably as small and portable units of human trade throughout history," researchers David MacHugh and Daniel 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 for millions of people in the developing world. Strange as it might seem, we should rightfully include those skinny animals 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 of wild horses. In pairs, share your information with your partner and discuss both texts to combine all the details, so you could answer the questions in Exercise 5.
Text A. DNA Hints at Origins of Domestic Horses
By Sarah Graham
The last sighting of a wild horse population occurred in 1969 in Mongolia. A far more common sight is a domestic horse, whether on a farm or a racetrack. Now scientists have shed new light on how these magnificent beasts came to be controlled by humans. According to a report published online this week by the Proceedings of the 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, the findings could further the study of language evolution.
To track the trail of domestic horses, Thomas Jansen of Biopsytec Analytik in Rheinbach, Germany, and his colleagues sequenced DNA from 318 horses representing 25 different breeds. Specifically, the team analyzed mitochondrial DNA (mtDNA), which is inherited from the mother, and compared the recent samples to previously published DNA data from 334 other animals. The researchers identified 17 distinct types of mtDNA and calculated that 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 the mares, 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 procedure may have slowly spread from a single starting point. In that case, the authors write, "the knowledge and the initially domesticated horses themselves would have spread, with local mares incorporated en route, forming our regional mtDNA clusters." (From Scientific American Online, July 16, 2002)
Text B. Modern Horses Have Many Origins
By Julia Karow
About 6000 years ago, somewhere in the Eurasian grassland steppe, man started to capture and tame wild horses--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 had already lived with humans for several thousand years. Now genetic evidence from modern and ancient horses, published in today's Science, completes the picture: the taming of horses did not occur in only one place, but in several, geographically distant locations.
Researchers from Sweden and the U.S. analyzed parts of the mitochondrial DNA of 191 domestic horses from ten different breeds, including the Icelandic Pony, the Arabian horse and the (American) Standardbred. They also included DNA sequences from 12,000 to 28,000-year-old horse bones found in Alaska and from 1,000 to 2,000-year-old horse remains from Northern Europe in the comparison. Mothers alone pass on mitochondria to their offspring, which is why the data represents only the maternal line. But the DNA samples from the modern horses differed so much from each other that they probably originated from several different groups of domesticated horses. And the genetic variation within each breed indicates that probably more female horses and only a few studs were used for breeding--a practice that continues today.
Rather than giving away domesticated horses, people in Eurasia probably taught each other techniques for capturing and keeping wild horses from their own area. That's why today's breeds still carry the genetic hallmarks of many different wild populations. (From Scientific American Online, January 19, 2001)
Exercise 5. Answer the following questions:
1. When was a wild horse population seen for the last time?
2. What methods were used to determine the time of horse domestication?
3. What genetic material was used in each study described in the texts?
4. When and where did domestication of horses start?
5. How was domestication of horses performed?
Exercise 6. Make up a list of the 10 key facts about studies of domestication. Agree on the final list of facts with the whole group.
Then summarize everything you now know about domestication of wild animals into one report.
Последнее изменение этой страницы: 2016-03-25; Просмотров: 628; Нарушение авторского права страницы