Cloning is still very much a science in its infancy. There have been relatively few successes, and many disappointments along the way. And many people see serious problems in the difficulties experienced so far, indications perhaps that cloning in mammals should stop before it is fully started. The problems start with the very first example of successful mammalian cloning – Dolly herself!

When Dolly was born she seemed a fit, healthy sheep. She went on to prove her normality by giving birth to Bonnie (fathered by David the ram) followed by several other non-cloned lambs. However, when she was only five years old she developed quite severe arthritis – something sheep are prone to but which normally affects them when they are older.

Scientists looked at the microscopic appearance of Dolly’s cells – and the telomeres at the end of her chromosomes, which shorten with age, seemed about 20% shorter than those of other sheep the same age. By the time she was six, Dolly had an incurable lung disease – again not unusual in a sheep kept permanently indoors – and finally had to be put down on February 14th 2003. She was only six years old.

The average sheep lives from 10 to 12 years. Dolly’s mother was 6 years old when her cell was removed and cloned. Inevitably people wondered if Dolly’s real age was her own age added to that of her mother, which would give 12 years old; quite a respectable age for a sheep.

Scientists are still working to try and discover whether Dolly really did suffer from premature ageing or not. Obviously the answer to that question has far-reaching implications for the long term success of cloning.