Is a clone an example of the species that was cloned? Or does the clone represent a new species, one very similar to the original but different nonetheless? As we've learned during the last 25 years, subtle distinctions in the genome are responsible for substantial variation. For example, the similarity between the human genome and the mouse genome is approximately 85%. The human genome and the chimpanzee genome share 98% commonality. The genome of Home sapiens sapiens - the current version of human beings - and the genome of Homo neanderthalensis have only a 0.5% difference in structure. But no one would mistake a 2010 resident of New York City, Johannesburg, or Hong Kong for a Neanderthal man.
Complex systems are critically sensitive to small changes in initial conditions. This deep concept, encapsulated by the descriptive "butterfly effect", was made famous by Michael Crichton's character Dr. Ian Malcom in Jurassic Park. As he explains chaos theory to Dr. Ellie Sattler, a paleobotanist, Malcom notes that a butterfly flapping its wings in the Amazon rain forest can cause a tornado in the American Midwest. The butterfly effect is a key component of most, if not all, physiologic processes.
It is notoriously difficult to predict the exact manner in which a complex system will respond to a specific small change in initial conditions. For example, turning on one specific gene - a small change, in the context of the 20,000 or so genes in human DNA - may cause a cell to overdo its job, underperform, die, or become cancerous. Any of these states may result in local pathology, a low level of disease, chronic disease, or death of the individual.
The field of embryology and development involves deeply complex systems. The mechanisms of development are beginning to be understood after 100 years of investigation. In embryology, cells respond to chemical signals generated by processes occurring in other locations. Their responses affect activities elsewhere. Many of these processes are random, based on molecular interactions, and if too much randomness is present normal development will fail. For example, small perturbations can disturb the process and result in the death of the developing embryo, as evidenced by the fact that up to 75% of embryos fail to mature successfully.
Cloning, achieved by somatic cell nuclear transfer, effects substantial alterations in the process of reproduction. The vast majority of these alterations are unknown and their effects can only be guessed at. Any single alteration could cause profound changes in the physiology of any clone that survived the mechanisms of development. But many changes in initial conditions are introduced during cloning, not only one. The clone may walk and talk like a human and we may believe she is human, but the true nature of the cloned organism will only be revealed over time. It is not guaranteed that a human-appearing clone will turn out to be human at all.
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