1990’s, however, the only actual means of producing
animal clones was by splitting early embryos—
mimicking the natural process that creates identical
twins—and that was difficult to achieve in mammals.
It was not until 1993 that scientists at George Wash-
ington University succeeded in splitting a human
embryo. In the following year, Neal First of the Uni-
versity of Wisconsin accidentally discovered a new
means of inducing embryos to split, cloning a set of
bovine embryos.
Milestones in Cloning First’s discovery was rapidly
adopted by scientists attempting to clone mammals
by means of nuclear transfer as a way of multiplying
the chances of bringing an embryo to term. It as-
sisted scientists at the Roslin Institute in Scotland to
produce a sheep cloned in this fashion, nicknamed
Dolly, whose birth was announced in February,
- Scientists at the University of Hawaii Medical
School announced the birth of Cumulina, a mouse
cloned by their own variation of the nuclear transfer
method, in July, 1998. Nuclear transfer remained a
somewhat haphazard process, however; Dolly was
the only success in 277 experimental runs.
Dolly was followed a year later by Polly, the first
clone of a genetically modified ewe. The difficulties
of reproduction by nuclear transfer, however, cou-
pled with the difficulties of initial genetic modifica-
tion, meant that progress in developing breeding
populations of genetically modified animals was
slow. The possibility of developing any large-scale in-
dustrial enterprise by this means still seemed remote
at the end of the 1990’s.
The first recognized live birth of a cloned pri-
mate produced by embryo splitting was a rhesus
monkey born at the Oregon Regional Primate Re-
search Center in 1999. It subsequently transpired,
however, that techniques used by U.S. fertility clin-
ics in the late 1990’s had often resulted in acciden-
tal embryo splitting, increasing the probability of
identical twin births by a factor of four. Planned re-
search in human cloning was, however, focused
throughout the 1990’s not on reproductive cloning
but on therapeutic cloning, involving the produc-200 Cloning The Nineties in America
Dolly the sheep, the first animal to be cloned from adult cells. (AP/Wide World Photos)