Should we always say it twice?: Identical twins are not really identical
|March 30, 2011||Posted by O'Leary under Intelligent Design, Genomics|
From “No Two of Us Are Alike — Even Identical Twins: Pinpointing Genetic Determinants of Schizophrenia”, (ScienceDaily, March 28, 2011) we learn
Singh looked at about one million markers of identical twins (and their two parents) where only one twin had schizophrenia. “The most informative feature of schizophrenia is that it sometimes runs in the family. So, for example, the risk of developing schizophrenia is much higher if your brother, sister, mother or father have the disease,” says Singh, noting in the general population about one percent have schizophrenia. “We started with the belief that monozygotic twins are genetically identical, so if one member of identical twins has schizophrenia, then the risk for the other twin should be 100 percent, if it’s all due to genes. However, studies over the years have shown that the risk of the disease in both twins is only 50 percent.” That means either the twins are genetically not identical or the familial disease involves non-genetic (random) effects.
Singh and his team have now demonstrated that the monozygotic twins are not genetically identical.
The part I find curious is, “We started with the belief that monozygotic twins are genetically identical, so if one member of identical twins has schizophrenia, then the risk for the other twin should be 100 percent, if it’s all due to genes.” Well, a survey of group homes serving people with mental disorders could have established early in the game that 100% of monozygotic twins did not share the disease, and thus ended the discussion over identican-ness. So we could simply have started with the assumption on which Dr. Singh has now ably provided us with information.
One thing that Mario Beauregard and I pointed out in The Spiritual Brain is that, in a given dyad, there is generally a dominant and a less dominant twin. This fact alone will likely lead to non-shared developments.
See also: Identical twins: The differences explored
Identical twins does not mean identical minds