Pope puts stress on 'gay threat' from BBC News Europe
"If tropical forests deserve our protection, humankind... deserves it no less."
Pope Benedict has called for "an ecology of the human being."
Pope Benedict XVI has said that saving humanity from homosexual or transsexual behaviour is just as important as saving the rainforest from destruction.
He explained that defending God's creation is not limited to saving the environment, but also protecting man from self-destruction.
The pope was delivering his end-of-year address to senior Vatican staff.
His words, later released to the media, emphasised his total rejection of gender theory.
Pope Benedict XVI warned that gender theory blurs the distinction between male and female and could thus lead to the "self-destruction" of the human race.
Gender theory explores sexual orientation, the roles assigned by society to individuals according to their gender, and how people perceive their biological identity.
Gay and transsexual groups, particularly in the United States, promote it as a key to understanding and tolerance, but the pope disagreed.
When the Roman Catholic Church defends God's Creation, "it does not only defend the earth, water and the air... but (it) also protects man from his own destruction," the pope said.
"If tropical forests deserve our protection, humankind... deserves it no less," the 81-year-old pontiff said, calling for "an ecology of the human being."
It is not "outmoded metaphysics" to urge respect for the "nature of the human being as man and woman," he told scores of prelates gathered in the Vatican's sumptuous Clementine Hall.
The Catholic Church opposes gay marriage. It teaches that while homosexuality is not sinful, homosexual acts are.
The pope uses his traditional end-of-year speech to offer his Christmas greetings and say a few words about what he considers the important issues of the day.
This year, Pope Benedict also deplored the tendency to depict the Catholic church's World Youth Day, which he attended in Sydney earlier this year, as mere spectacle.
He stressed that the event should not be considered a "variant of modern youth culture, as a kind of ecclesiastical rock festival with the Pope as the star," but as the fruition of a "long exterior and interior path".