One reason why a sheep, a less well-understood experimental subject than the laboratory mouse, should have proved easier to clone may stem from differences in the initial stages of the two species’ embryonic development. After reaching maturity in the ovary of the mother, the unfertilized eggs of all mammals accumulate a supply of proteins, and the means of producing fresh protein. In this way, the mammalian egg brings with it a larder for the embryo to make use of until its own genes activate and supply this requirement themselves. The sheep embryo disposes of its store properly and need not depend on its own genes until the sixteen-cell stage, four cell divisions successive to fertilization, while in contrast, the mouse embryo commences this process more precociously, becoming reliant on the activity of its own genes after just the first division when the fertilized egg becomes two cells. Therefore, a foreign nucleus introduced into a sheep egg exploits a respite in its host’s biological development, allowing it to adapt to its new role before assuming genetic control.
　　Concomitantly, a nucleus introduced into a mouse egg must acclimatize quickly for its genes to be able to direct embryonic development within a single cell division, so perhaps there is insufficient time for the extensive re-programming of compulsory gene activity. The human embryo is thought to rely on its own genes after three cellular divisions, which might or might not provide time enough for a foreign nucleus to acclimate. However, were scientists to comprehend the nature of the indispensable re-programming then there is every likelihood that both mice and humans could be cloned.
　　Despite the long-standing availability of this technology, there has until recently been little interest in it. Some people suffering from infertility as a result of rare hereditary diseases could produce offspring, but cloned individuals may be at risk given scientists’ limited knowledge of the long term effects of allowing an "old" adult cell nucleus to commence life again in an egg. The nucleus of a skin cell could have accumulated a multitude of genetic mistakes of no consequence to its role in the skin, but the same cell could prove deleterious in other tissues, or immensely increase the probability of the affliction with cancer. The threat to general human health posed by cloning, as opposed to the individual, is difficult to determine, but the risks are almost certainly lower than those encountered in the effective inbreeding of consanguine marriages, and thus there are no scientific grounds per se for banning cloning. Like other practices inconsequential to the physical well being of humanity, but generally deemed undesirable on moral or social grounds, the prohibition of human cloning will ultimately rest with only a simple pragmatic decision.

The author suggests that all of the following is true concerning the cloning process EXCEPT（）.