From an evolutionary standpoint, it makes sense that males of a given species tend to be attracted to females and vice versa because this will encourage frequent reproduction and survival of the species. But if that’s the case, then why do same-sex attractions exist? This is a question that has long been of interest to scientists. In the video below, Dr. Alice Dreger breaks down some of the key things we’ve learned from the research so far.

As Dreger explains toward the beginning, it’s complex to study this topic because “sexuality and gender have interplayed components in them.” In other words, while there’s a popular idea out there that gender and sexual orientation are totally separate, research tells us that you can’t study these things in isolation.

Dreger goes on to explain some of the popular theories on the origins of homosexuality, some which suggest that being gay could actually be an advantage and something that makes our species more resilient. As some evidence of this, she talks about the fa’afafine of Samoa (which you can learn more about here). Fa’afafine are biologically male in terms of their chromosomes and gonads and are almost exclusively attracted to men. They’re considered a third gender, although they don’t identify as transgender or as gay (those identities don’t really exist in Samoa. This is mind-blowing to a lot of people because this means that gay and trans are social constructs that don’t have universal meaning cross-culturally—but that’s a discussion for a whole other article!). At any rate, fa’afafine don’t typically reproduce, but they do tend to invest a lot of resources in the children of their siblings.

Toward the end of the video, Dreger addresses a question that invariably comes up in response to videos and articles about why some people are gay, which is this: why are some people straight? Dreger tackles this question in a thoughtful way and makes an important point: “Straight people have been less interesting to scientists than gay people in terms of where they come from…Straight people remain largely a mystery as to how they operate. What makes them straight, we don’t really know.”

To learn more, check out the full video below.