One reason why a sheep, a less well-understood experimental subject thanthe laboratory mouse, should have proved easier to clone may stem fromdifferences in the initial stages of the two species’ embryonic development.Line After reaching maturity in the ovary of the mother, the unfertilized eggs of all(5) mammals accumulate a supply of proteins, and the means of producing freshprotein. In this way, the mammalian egg brings with it a larder for the embryoto make use of until its own genes activate and supply this requirementthemselves. The sheep embryo disposes of its store properly and need notdepend on its own genes until the sixteen-cell stage, four cell divisions(10) successive to fertilization, while in contrast, the mouse embryo commences thisprocess more precociously, becoming reliant on the activity of its own genesafter just the first division when the fertilized egg becomes two cells.Therefore, a foreign nucleus introduced into a sheep egg exploits a respite in itshost’s biological development, allowing it to adapt to its new role before(15) assuming genetic control.Concomitantly, a nucleus introduced into a mouse egg must acclimatizequickly for its genes to be able to direct embryonic development within a singlecell division, so perhaps there is insufficient time for the extensive re-programming of compulsory gene activity. The human embryo is thought to rely(20) on its own genes after three cellular divisions, which might or might notprovide time enough for a foreign nucleus to acclimate. However, werescientists to comprehend the nature of the indispensable re-programming thenthere is every likelihood that both mice and humans could be cloned.Despite the long-standing availability of this technology, there has until(25) recently been little interest in it. Some people suffering from infertility as aresult of rare hereditary diseases could produce offspring, but cloned individualsmay be at risk given scientists’ limited knowledge of the long term effects ofallowing an "old" adult cell nucleus to commence life again in an egg. Thenucleus of a skin cell could have accumulated a multitude of genetic mistakes of(30) no consequence to its role in the skin, but the same cell could prove deleteriousin other tissues, or immensely increase the probability of the affliction withcancer. The threat to general human health posed by cloning, as opposed to theindividual, is difficult to determine, but the risks are almost certainly lowerthan those encountered in the effective inbreeding of consanguine marriages,(35) and thus there are no scientific grounds per se for banning cloning. Like otherpractices inconsequential to the physical well being of humanity, but generallydeemed undesirable on moral or social grounds, the prohibition of humancloning will ultimately rest with only a simple pragmatic decision. Which of the following hypothetical scientific discoveries, if made, would weaken the author's arguments concerning the ethical risks of human cloning()
A. Through careful and documented study, cloning proves to be less risky than consanguineous breeding.
B. A laboratory process for reducing the number of stages in the cell division process is developed.
C. A non-cloning method for curing human fertility is discovered, thereby reducing the need to rely upon cloning.
D. A procedure for easing the acclimation of a foreign nucleus in the embryonic host is established.
E. A means of assessing genetic mistakes in a foreign nucleus before its implementation into a clone is devised.