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 díHistoire 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.