It appears that a growing number of heterosexual-identifying men are seeking out pornography featuring performers who were born male, retain their penises, but otherwise are female. These trans women performers and sex workers are often called shemales or tgirls, although many consider both terms pejorative. Typically, their transitions include the use of feminizing (i.e., female) sex hormones and breast enhancement surgery.
Many heterosexual men with this sexual preference are understandably confused and question their sexual identities. I've worked with several of them in my clinical practice. The objective of our work together is to increase understanding, acceptance, and integration of their sexual interest within the context of their heterosexual identities (much like any other unusual sexual interest).
As for the exact nature and origins of this sexual interest, nobody is entirely sure. Some, such as Dan Savage of Savage Love, have suggested that what drives these men is a sexual interest in penises, but not men. Framed this way, trans women with penises are a man-free and safe way to satisfy a sexual interest in penises.
Another theory suggests that a sexual interest in trans women with penises is related to, or a manifestation of, autogynephilia. Autogynephilia is a paraphilia (an unusual sexual interest) seen in heterosexual men, and characterized by sexual fantasies of having a woman's body.
A study recently published in the journal Psychological Medicine is the first to shed some light on this topic.
The main findings were that men with gynandromorphophilia really are heterosexual (and not homosexual or bisexual), but exhibit a unique pattern of sexual responding to stimuli featuring trans women with penises.
You can read the full academic journal article here: link.
Gynandromorphophilia (GAMP) is sexual interest in gynandromorphs (GAMs; colloquially, shemales). GAMs possess a combination of male and female physical characteristics. Thus, GAMP presents a challenge to conventional understandings of sexual orientation as sexual attraction to the male v. female form. Speculation about GAMP men has included the ideas that they are homosexual, heterosexual, or especially, bisexual.
We compared genital and subjective sexual arousal patterns of GAMP men with those of heterosexual and homosexual men. We also compared these groups on their self-ratings of sexual orientation and sexual interests.
GAMP men had arousal patterns similar to those of heterosexual men and different from those of homosexual men. However, compared to heterosexual men, GAMP men were relatively more aroused by GAM erotic stimuli than by female erotic stimuli. GAMP men also scored higher than both heterosexual and homosexual men on a measure of autogynephilia.
Results provide clear evidence that GAMP men are not homosexual. They also indicate that GAMP men are especially likely to eroticize the idea of being a woman.