¡i©ú³ø±M°T¡jOn 13 January 2000 a group of US scientists announced the first successful cloning of a monkey, which was named "Tetra".

However, as with other breakthroughs scientists had achieved in this field, the news met with anxious concern from certain groups, who claimed that cloning technologies might have become too advanced to be ethical (¦X¥G¹D¼wªº).

1. Tetra the monkey

Tetra was the first primate (ÆFªø¥Ø°Êª«) created by cloning. In a process called "embryo splitting" (­F¤Àµõ), scientists at the Oregon National Primate Research Center split the cells in the embryo at the 8-cell stage, when the fertilised egg (¨üºë§Z) had undergone three cell divisions. Four identical two-cell embryos were produced, but, in the end, only one of them was successfully delivered. That was Tetra, which was born in October 1999. The scientists announced the news several months later.

Comparisons have often been made between Tetra and Dolly the sheep, the first cloned mammal (­÷¨ÅÃþ°Êª«). Dolly, born on 5 July 1996, was created differently from Tetra (by nuclear transfer). The female sheep died in 2003.

In fact, since the early 1960s, scientists have been effectively cloning animals. Two cows (named Noto and Kaga) were cloned in 1998 in Japan and duplicated several thousand times, enabling the production of better meat and milk. The following is a list of other animals that have been cloned:(¨£ªí)

2. Human cloning - the most controversial issue

Because of scientists' successes in cloning animals, human cloning, the creation of a genetically identical copy of a human, has become an issue that cannot possibly be sidestepped. Two types of theoretical human cloning are being discussed: therapeutic cloning (ªvÀø©Ê½Æ»s) and reproductive cloning (¥Í´Þ©Ê½Æ»s). The former refers to the cloning of cells from a human for use in medicine and transplants (¾¹©x²¾´Ó), while the latter is about the "copying" of the whole person.

Advocates and opponents of human cloning differ profoundly. Those who support human cloning argue that, with therapeutic cloning, scientists will be able to generate tissues and whole organs to treat patients who otherwise cannot obtain transplants, to avoid the need for immunosuppressive drugs (§K¬Ì§í¨î¾¯, which are used to prevent the rejection of transplanted organs and tissues), and to counter the effects of aging.

Those who oppose human cloning are worried that the technology is not sufficiently developed to be safe and that it could be used unethically (e.g. to clone humans from whom organs would be harvested (ºK¨ú)).

Currently many countries (such as Australia, Canada, the UK and the US) have laws that prohibit certain or all kinds of human cloning.

3. Human cloning in popular culture

Like time travel (®É¶¡®È¦æ), human cloning features frequently in films and science fiction. In Aldous Huxley's Brave New World (¡m¬üÄR·s¥@¬É¡n), human cloning is used by the government to control the size of the population. The 2005 film The Island (¡mÁÀ®q«qÅÜ¡n), which stars Ewan McGregor and Scarlett Johansson, tells the story of a group of cloned humans who are locked up on an island and whose organs are to be harvested.