8. Give an example of a positive effect of selective breeding. (It can be ascertained from the article, our lesson, or the supplemental videos) ReadWorksSelective BreedingCharles Darwin may have been the first to describe the process of selective breeding, butthe practice may be more than 2,000 years old. The Romans are said to have practiced selectivebreeding among their livestock, favoring cows that produced a lot of milk. But it wasn't until the18th century that farmers began practicing it on a large, industrial scale.Today, farmers breed chickens to have extra-large breasts and to lay a lot of eggs. A wildfowl-a chicken that lives in the woods-lays between 20 and 30 eggs per year. In contrast, achicken born out of selective breeding can lay as many as 300 eggs per year.In the same way that chickens are selectively bred for having more meat and laying agreater amount of eggs compared to wild chickens, cattle are often selectively bred either formore meat or for more abundant milk production compared to cattle in the wild. Over thecourse of the 1700s, the size of bulls sold for slaughter increased dramatically-from around300 pounds (about 140 kilograms) to nearly 800 pounds (about 360 kilograms)–as a result ofselective breeding. Also as a result of selective breeding, the dairy cow, which does not displaya lot of girth or muscle, can produce enough milk for 10 calves. One can identify a dairy cow byits udders, which can hold over 5 gallons (over 19 liters) of milk.Even though people selectively breed to yield animals with desired traits, there aredangers to selective breeding. Temple Grandin, an animal welfare advocate, notes thatbreeding animals for size and strength interferes with natural animal processes. Breedingroosters for muscle, for example, can make them top-heavy and unsteady on their feet,interfering with their courtship dances. This, in turn, can alienate them from hens.Speaking of hens, what about those that were bred to lay 300 eggs per year? Laying oneegg a day makes a hen's bones brittle, since the eggs soak up the bird's calcium supply. Andwhat about so-called broiler chickens-the ones that are bred for their large breasts? Often,their bodies grow so fast that their skinny legs can't support them.Cows required to produce enough milk for 10 calves tend to burn out quickly. Cows notsubject to selective breeding can live up to 30 years without burning out. But prolific dairy cowstend to make it just four or five years before they are considered worthless, and then they aresent to be slaughtered.Selective breeding comes with both benefits and drawbacks. Think of all the joy thatdogs have offered humans in the form of companionship over the last 100 years. Selectivebreeding is to thank for man's best friends. And yet, the pain and suffering that livestockendure makes us think twice. It is important to keep in mind that, in some cases, the negativeconsequences of selective breeding may outweigh the positive. Selective BreedingCharles Darwin, a British naturalist who lived in the 19th century, is best known for hisbook On the Origin of Species. In it, Darwin established the idea of evolution that is widelyaccepted today. He proposed that all species alive have evolved through adaptation to theirsurroundings. Natural selection, the process by which varied traits that increase survival andenable reproduction are passed down from generation to generation, is probably the mostfamous principle from the book. Darwin's book also addresses the perhaps less well-knownconcept of artificial selection. Today artificial selection is more often called "selectivebreeding." Selective breeding involves breeding animals or plants for a specific, typicallydesirable trait. By doing so, the desired genes from the plant or animal will be passed on to itsoffspring.Dog breeding is one of the most common examples of artificial selection. You need onlyto tune into a dog show on TV to see the power of selective breeding at work. Crossbreeds, forexample, are dogs born from parents of two different breeds. Mixed breeds are born fromparents of more than two breeds, and pure breeds are born from a single breed. All threevarieties are featured in most dog shows. Many of these dogs were bred to achieve certaindesirable physical or behavioral traits.Beyond the context of dog shows, dogs are a particularly interesting example ofselective breeding. After all, we call dogs "man's best friend" for a reason. Dogs originallyevolved from wolves. Eventually, humans were breeding different types of dogs to accomplishcertain jobs. For example, some dogs were bred to hunt well. Others were bred with desiredtraits to herd cattle. But it was a trait known as "tamability," or a dog's ability to be tamed andlive among people, that resulted in humans keeping dogs as pets. Now that many people liverelatively quiet, domestic lives, how well a dog can herd sheep is not of huge importance.What matters most is whether a dog makes a good companion.

Name: 8. Give an example of a positive effect of selective breeding. (It can
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Description: 8. Give an example of a positive effect of selective breeding. (It can be ascertained from the article, our lesson, or the supplemental videos) ReadWorksSelective BreedingCharles Darwin may have been the first to describe the process of selective bre