A surprisingly common paraphilia among otherwise heterosexual males approaching middle age is a desire for sex with transsexuals: males who appear to be women with developed breasts but still have a penis. In many countries, entire neighborhoods are sometimes dedicated exclusively to prostitutes of this category. Why? Most likely the normal sexual urge of some male children toward the opposite sex is short-circuited by their ignorance of female anatomy—especially if they have no female siblings in the family or have not been exposed to full female frontal nudity in life or in pictorial form (to which many males growing up prior to the 1970s would not have been readily exposed).

Instead, the male child fills in his imagination with what he knows best—his own body. He imagines the female form with the penis and fuses this imagery with his earliest and arguably most intense sexual sensations. What happens next, of course, remains a mystery. Upon discovering the true form of female genitals, some males react with aversion while others decide that what women really have is even better than what they imagined and go from there. Others, however, continue to associate an intense desire with their childhood memory of women with male genitals.

an excerpt from Serial Killers: The Method and Madness of Monsters