Cloning a human is more challenging than cloning a sheep for several reasons:
Ethical considerations: There are significant ethical concerns surrounding human cloning. The prospect of creating genetically identical human beings raises complex moral and social issues, including questions of individuality, identity, autonomy, and the potential for exploitation. These ethical considerations have led to legal and societal restrictions on human cloning, which further complicate the process.
Technical difficulties: Cloning is a complex and technically demanding process. It involves replacing the nucleus of an egg cell with the genetic material from a donor cell and then stimulating that egg to develop into an embryo. While this procedure has been successfully performed in other animals, such as sheep (as seen in the famous case of Dolly the sheep), the success rate in cloning mammals remains relatively low. Furthermore, human embryos are more delicate and sensitive compared to those of animals, which adds to the technical challenges.
Limited availability of human eggs: The process of cloning requires a supply of human eggs, which are not readily available in large quantities. Obtaining human eggs for research purposes raises ethical and legal concerns, and it is difficult to procure a sufficient number of eggs for successful cloning experiments.
Genetic complexity: Humans have a much more complex genetic makeup compared to sheep or other animals. The human genome contains approximately 3 billion base pairs, and the intricacies of human genetic regulation are not fully understood. Cloning a human would require precise manipulation and reprogramming of all the genes and genetic processes, which poses significant technical challenges.
Developmental challenges: Cloned animals often face various developmental abnormalities and health issues. While Dolly the sheep was successfully cloned, she suffered from premature aging and other health complications. The potential risks and ethical concerns associated with cloning a human and the potential long-term effects on the cloned individual are significant barriers to attempting such a procedure.
Given these ethical, technical, and scientific complexities, the scientific community and society as a whole have largely refrained from pursuing human cloning, instead focusing on other areas of scientific research and medical advancements.