in 1997 photographs of a sheep called dolly appeared on the front page of newspapers around the world. she looked quite ordinary, but dolly was different from other sheep. she was an identical copy of another adult sheep. in other words, she was a clone. before dolly, scientists had only been able to clone large animals using cells taken from embryos. they had tried to do it using cells from adult animals, but it hadn't worked until now. that's why dolly was so special.
Lots of animals have been cloned since than,including cows , monkeys and cats. cloning technology is also being used to try to keep some animals from becoming extinct. but we still don't understand the technology very well. the scientists who created dolly tried 276 times before they were successful. many cloned animals die soon after they are born, and those that survive often become ill later.
since dolly's arrival, some people have suggested that humans might also be cloned one day. the idea is very controversial. a lot of people think it would be wrong, including some of the scientists who created dolly. but others think it would be okey in some situations, such as helping scientists to find a cure for a disease. whether it's right or wrong, cloning humans will be possible one day. it's up to us to decide what happens next.