If natural selection favours individuals who leave behind lots of descendants, why do homosexuals exist?

Filmmaker Bryce Sage, who describes himself as "openly gay and proudly flamboyant," set out to answer that question in his new documentary, Survival of the Fabulous, which aired Thursday at 8 p.m. on CBC-TV's The Nature of Things.

The film follows Sage on a humorous, personal journey that takes him around the world to talk with scientists who are researching topics ranging from the neuroscience of gay sheep to the effect of birth order on your odds of being gay.

Sage also examines the nature and nurture components of his own life by visiting his family in Port Hope, Ont.

Sage spoke to CBCNews.ca about the experience of making the film and what he learned about the science of homosexuality.

What made you interested in making this film?

Well, I guess, ever since I came out of a closet in a small town where it's not the idealized environment to be different and all that, I've always wondered, "Why is anyone gay?" Because if we're born this way, which I feel like I was, then why would something that makes you so unlikely to reproduce exist to begin with? It doesn't seem to make any natural sense.

That's a very scientific question.

Yes. I've always been obsessed with genetics, even though I ended up choosing a path in film. Ever since I saw Jurassic Park, I wanted to be a genetic engineer so I could make dinosaur; or I particularly wanted to make half-human, half-animals. But a wise guidance counsellor told me that's not very likely, the mad scientist route is not really a career option. So they encouraged me to go into storytelling instead.

But that lingering question of what makes us who we are, that question of nature versus nurture has always been something that fascinated me.

It sounds like you were asking a number of questions in your film. What was the first one you set out to tackle?

I've always felt in my gut, in my heart that I'm born gay. But as science says, you can't just take something for granted. So the first big question is: Are we actually born gay? If, in fact, you are born gay, what is making you gay? Do genes play a role? Is it hormones? Is it a natural part of development in that genes don't even have an influence? Overarching all of this I had very simple questions that I didn't realize were a lot more loaded and a lot more complicated.

What do you mean they were a lot more loaded and complicated?

Well, I still can't say definitively that yes, we are born gay. Most of the evidence seems to indicate that there is a very high degree of likelihood that we are born gay. For example, one of things in the doc is we have our brain bombarded by male and female erotica to see what's going on while we're in an MRI. And the parts of the brain that are activating are parts that — the limbic system, the hypothalamus, things like that that — tend to be pretty developed by the time you're born. They're not as malleable as other parts of the brain. But even if that is true, it doesn't necessarily say for certain that one is born gay.

Long story short, I think as a non-scientist, when you have these sets of questions, you very quickly realize that science is just so much more complicated than you thought — that there's very rarely a case of black and white answer, it's usually a lot more grey.

You had a lot of weird studies in the film. Which one did you think was the strangest?

I guess the one that felt the weirdest was probably the brain MRI. It's beyond my understanding to know that you can tell from looking at four-second images exactly what's going on in the brain. I couldn't feel a remote bit of erotic pleasure whatsoever during the entire experience. But somehow they're able to register that in the brain.

What was it like?

It's like you're in this tube that couldn't be more claustrophobic. You're trapped inside this magnetic thing. You're fearing for your life. The sound is this blaring buzz and kind of ringing sound that you hear the entire time. It's about the most undesirable context you could possibly be in.

And then you see just little flashes of pornographic material. And I can tell just by looking at it OK, yeah, it's a hot guy or it's a woman. But either way, it's not like I'm even remotely capable of being turned on physically by this. But I guess somehow, just in registering the image, that's enough.

What made it so important for you to make the documentary so personal?

The reason I felt the need to be personal is this subject is so important. If you can prove that sexuality is not a choice, it's as much a part of us as our gender or race is, it's completely unchangeable, there's no doubt in my mind that discrimination would go away. That's almost essential to that happening.

But if you do just the talking head doc, the only people that watch it are the people that already believe. But I feel like you've got to be almost subversive with your politics.

So by putting myself in the story, it makes it a lot more fun, it makes it a journey, it makes it more entertaining. It's almost like, what's that song from Mary Poppins? "A spoonful of sugar helps the medicine goes down."

You feature quite a few Canadian researchers in your film. Were you surprised that so many Canadians were studying gay-ness?

Yeah, that was certainly interesting. Where it may not be so much of a surprise is that Canada is one of the most progressive places when it comes to sexuality and the freedom that gay and lesbian people have in comparison to other countries like the States. And from what I've since learned talking to the scientists, it's a lot easier in Canada to get funding for scientific research into this kind of thing than it is in the United States, where it is still quite a controversial subject matter.

What was the most surprising thing you learned over the course of your research?

Probably one of the most surprising things was that a lot of people assume that … genes would code for homosexuality, that they make you gay. But they're actually more a code for attraction for men. And it just so happens when men get these genes, they are gay, but if women have these genes, they actually become more attracted to men, as opposed to making them lesbians.

I guess that's something that's not obvious. You'd assume that gayness in men and women might be kind of the same process.

Yeah, we don't feature lesbians in the documentary at all because, according to the science, what causes and influences sexuality in men is very different from what causes and influences sexuality of women.

We felt like we'd better not to muddy the waters by trying to address both when it's such a complicated subject matter to begin with. That would be the sequel, right?

You mention that everything ended up being a lot more complicated than you thought. In the end, did you feel like you got enough answers?

Can I move on? [laughs]

Definitely, I know from all the evidence I gathered, and all the scientists I talked to that all of these things help to explain why homosexuality survived. I'll never know within my lifetime exactly what made me gay. But I certainly feel like I have enough. Even in this greyness, I have enough of an understanding that there is biology to explain who we are and we did not make a choice.

Click here to view the trailer on a mobile device