Pennisi E, Vogel G
Science. 2000 Jun 9;288(5472):1722-7. doi: 10.1126/science.288.5472.1722.
Often left out of news reports of cloned animals is the fact that for every 100 attempts, just two or three live offspring typically result. Now many researchers are going back to the lab to attempt to find out why. They are probing fundamental questions of cell biology, as well as trying to figure out whether there is something inherently flawed in "asexual" reproduction in mammals, or whether some problem lies in the in vitro component of the process. For now, the serious obstacles suggest that human cloning may be a long way off.
每进行100次尝试，通常只有两三个活体后代诞生。现在，许多研究人员回到实验室，试图找出原因。他们在探究细胞生物学的基本问题，同时也在试图弄清楚哺乳动物“无性”繁殖中是否存在内在缺陷，或者该过程的体外部分是否存在某些问题。目前，这些严重的障碍表明，克隆人可能还很遥远。
