當年今日﹕The cloned monkey
【明報專訊】On 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 (合乎道德的).
1. Tetra the monkey
Tetra was the first primate (靈長目動物) created by cloning. In a process called "embryo splitting" (胚分裂), scientists at the Oregon National Primate Research Center split the cells in the embryo at the 8-cell stage, when the fertilised egg (受精卵) 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 (哺乳類動物). 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:(見表)
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 (治療性複製) and reproductive cloning (生殖性複製). The former refers to the cloning of cells from a human for use in medicine and transplants (器官移植), 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 (免疫抑制劑, 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 (摘取)).
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 (時間旅行), human cloning features frequently in films and science fiction. In Aldous Huxley's Brave New World (《美麗新世界》), human cloning is used by the government to control the size of the population. The 2005 film The Island (《謊島叛變》), 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.
