This terrible and catastrophic condition persists as the great unresolved mystery of psychiatry. Why does it continue to aﬄict 1 in every 100 human beings in the course of their lifetime in every corner of the world, when schizophrenics themselves have a much lower fertility rate than average? Indeed, why does schizophrenia exist at all? What is it? And why did it come into existence in the ﬁrst place? We shall return to these issues later in this chapter, but ﬁrst we will examine the clinical nature of the condition.