www.aldaily.com

As a crusader against reproductive human cloning, Rudolf Jaenisch doesn't exactly fit the profile. He's motivated by neither politics nor religion. To make his case he appeals only to biology: human reproductive cloning will never succeed because fundamental facts of biology stand in the way. "As a scientist I have an obligation to warn against this" [...] "From a scientific point of view, human reproductive cloning is unsafe and unacceptable." Reproductive cloning, he argues, shortcuts basic biological processes, making normal offspring impossible to produce. And unlike the early days of in vitro fertilization, he says, this is not a technical hurdle that can be overcome with more advances—it's a fundamental biological problem. [...] Jaenisch carefully distinguishes between therapeutic cloning to produce stem cells—which he believes feasible, and supports—and human reproductive cloning. In both therapeutic and reproductive cloning, the nucleus from one cell is removed and placed into an unfertilized egg cell whose nucleus has either been deactivated or removed. In reproductive cloning, after a few divisions the egg cell is placed into a uterus where it will then hopefully develop into a fetus genetically identical to the donor of the original nucleus. In therapeutic cloning, however, the egg is placed into a Petri dish where it develops into embryonic stem cells—which have shown enormous potential for treating a host of ailments. [...] The biological problem is a principal one—how do you reprogram the nucleus so that it directs development of a normal animal? [...] With normal fertilization, the egg and sperm go through a long process of maturation, resulting in two genomes poised to activate the early embryonic genes. But cloning shortcuts that by trying to reprogram one nucleus's whole genome in minutes or hours. And according to Jaenisch, this process is not faithful. He believes that there isn't a single reproductive-cloning case in which the entire genome has been thoroughly reactivated. What has been achieved, he says, is everything from gross physical malformations to subtle neurological disturbances. "Most clones die immediately, some die later because of gene malfunction, others die at birth, and very few make it to adulthood. Now we have hard data to argue that these adults are not normal. We've looked carefully at adult cloned mice and found that they have significantly shortened lifespan and have, for example, major pathological alterations in their lives."

Que motivo apresenta o Prof. Jaenisch para sua posição contrária à clonagem reprodutiva?