Malaspina’s discovery shed light on a mystery that has long surrounded schizophrenia: How can so disabling a disease, which appears to be at least partly genetic, persist at such high rates when its victims so rarely reproduce? Schizophrenia is common – one in every 100 people suffers from it – and it tends to run in families. Siblings of schizophrenics are 10 times as likely to get the disease, and for identical twins the risk rises to 40 to 60 percent. Yet signs of schizophrenia do not appear until late adolescence and sometimes not until the fourth decade of life (women tend to develop symptoms later than men).