U.K. Study: Sexuality is Set Before Birth

A new U.K.-based study claims to prove that sexual orientation is decided before birth, being "hard-wired" into the human brain along with other key traits.

The report, a combination of work between the University of East London (UEL) and the Institute of Psychiatry, investigates sex differences in the startle response -- the eye-blink reaction to sudden loud noises.

The researchers announced on Friday in a press release that there may be a notable difference between homosexual and heterosexual subjects in terms of their brain circuitry. Since being startled is an involuntary reaction, rather than a product of environmental conditioning, researchers claim it is a strong indication that sexual orientation is determined before birth.

The research involved a technique known as prepulse inhibition (PPI), which measures the strength of response to loud noises.

Results showed clear differences between the groups, with lesbians showing a markedly stronger inhibition (a PPI of 33 percent) compared to straight women (just 13 percent).

Although the difference between heterosexual men and gay men is less extreme, 40 percent vs. 32 percent. respectively, researchers claim the difference is still significant.

"The startle response is pre-conscious and cannot be learned, " UEL's Dr. Qazi Rahman explained. "It is mediated by an ancient region of the brain called the limbic system which also controls sexual behavior."

Dr. Rahman added that the findings could have a large impact on the way sexuality is treated, both culturally and during health programs.