The causes of Schizophrenia are not clear, but Schizophrenia has long been attributed to faulty parenting. In cases, where Schizophrenia developed, the parents were often considered responsible. They were faulted for having been uncaring, or manipulative, or emotionally abusive. However, recent studies are now pointing to heredity and prenatal environmental factors as the chief culprits in this disease.

    Recent studies of identical twins have been used to demonstrate that heredity place a role in the development of Schizophrenia. These studies have shown that in cases where one identical twin is afflicted with Schizophrenia, the other twin has a 50% probability and also suffering from it.

     However, heredity is not believed to be the only culprit. Studies of fingerprints of identical twins have lent credence to the theory that prenatal environmental factors are likely contributors to the development of Schizophrenia. In studies of pairs of identical twins in which one is afflicted with Schizophrenia and one is not, abnormalities were found in the fingerprints of one-strip-third of the twins, always in the afflicted twin. Since fingers developed in the second trimester of pregnancy, the hypothesis has been proposed that the abnormalities in the fingerprints were due to a second-trimester trauma that affected only one of the twins and then this same trauma was a factor in the onset of Schizophrenia. Further research into this hypothesis is ongoing.

The author's purpose in this passage is to ....