Recent studies of identical twins have yielded impressive results. As mentioned before, more schizophrenic children are born in late winter and early spring. We don't know why. It has also been reported that male abusers in a family in England have an abnormal gene on the X chromosome. And, some men in the family had the defective gene but were not abusive.
Hyperactive parents are several times more likely to have a hyperactive child.
Disorders, such as migraine headaches and asthma, also seem to be inherited. Perhaps physiological and chemical processes, like hypoglycemia and proneness to alcoholism or epilepsy, are partly genetic. The power of the genes seems to be amazing, but we have to guard against exaggerating the role of genes. Having an unusual or surprising experience also causes stress. Donald Hebb found that chimpanzees had no fears until 4 months of age.