They also recorded that in some aboriginal cultures, such as the Keraki and Sambia peoples of Papua New Guinea, all young men entered into a relationship with an unmarried male warrior, sometimes lasting several years, as part of their rites of passage to manhood. Once completed, they ceased all homosexual contact and assumed sexual desires for women. If sexual orientation was totally biologically pre-programmed at birth, these men would have never been able to switch from homosexuality to heterosexuality with such apparent ease.

Lg people who are in forced marriages apparently convert to heterosexuality and if they leave that marriage, they revert to gay, easy-peasy.

Plus his example is bogus anyway, the author is actually using "young men" as a euphemism for little boys who were forced to become catamite sex toys for adult men.

The "young men" started engaging in heterosexual behaviour after the civil unions, due to the fact that the same sex behaviour sexual molestation was contrary to their sexual orientation.

The Keraki and Sambia tribes practiced pederasty as part of their 'Coming of Age' ceremonies, which has nothing to do with homosexuality. You can actually find videos taken by anthropologists showing the "young men" getting other rituals performed on them on YouTube.