Previously on this blog, I have looked at the various Biblical references to homosexuality. The most compelling argument in the Bible against homosexual behaviour is found in Romans 1. Those who condemn homosexuality find their strongest argument in the fact that it is "para phusin" - "against nature".
This phrase is contested, of course (a lot more contested than most preachers ever acknowledge when they preach against homosexuality). According to Paul, for example, it is also against nature for men to have long hair! In the context of Romans 1, there is also contention in how to translate the context. Paul is referring to people inflamed by lust, who give up their natural instincts and pursue same sex encounters without love and "against nature".
One of the foundations of this argument has always been that we don't see homosexual activity in animals. But this is not true. Recent research indicates that thousands of animal species exhibit homosexual behaviour. Read one hews release here and an older medical report here. This includes animals as "advanced" as dolphins, deer, lions, swans, and primates. And it is not "aberrant" behaviour, but natural in response to a variety of circumstances, including overpopulation (as humans are experiencing in most countries around the world), gender imbalances (as China is now experiencing with 40 million more young men than women), and threats to societal harmony.
One of the most interesting animals is black swans, where male homosexual swans will often "kidnap" a cygnet and raise it. Swans, of course, are monogomous throughout their lives. Even more interesting is that the research shows that animals raised by homosexual or lesbian parents fair better on average than those raised by a male-female couple.
This is not proof that God designed homosexuality, of course. Nor is it proof that humans are allowed to be homosexual. But, it does destroy a major argument that people who want to stand against homosexuality have used in the past. That argument is no longer available to them.