Science in Review — June 2013

Adult penguin with two chicks

Pairs of male penguins have been seen raising chicks. Is this homosexual behavior? Does it tell us anything about human behavior?

This is the second post in an ongoing series on the topic of biology and sexual orientation.

Last month, I talked about how the longstanding philosophical questions of the mind-body problem might inform or bias our understanding of how biology mediates sexuality. There was some question as to whether having a monist or dualist perspective is as significant to the topic as I theorized, but I still think it is relevant. In fact, I wonder whether the assumptions that stem from those perspectives are so fundamental to our thinking that they seem obvious and hard to imagine being any other way.

Nevertheless, setting aside the mind-body problem, the next assumption I found myself thinking about was the connection between animal behavior and human behavior. A lot of research on the biology of sexuality focuses on animal studies, either as a way to develop hypotheses to test in humans, or as an indirect way of understanding human biology and human behavior. This is for all of the usual reasons why animals are studied — lack of privacy concerns, (relative) ease of creating controlled conditions, shorter generation times (especially helpful for genetic studies), etc. Specific to this domain, there is also the ability to directly observe the behaviors of interest, rather than relying on surveys or other self-reported measures of behavior. But depending on one’s understanding of the relationships between humans and animals, this evidence will be more or less convincing.

And what sort of evidence are we talking about? As I have discovered, there are a lot of reports of homosexual behavior across the whole range of the animal kingdom. A comprehensive summary of the findings would be well beyond the scope of this blog; the material on the Wikipedia alone is more than I have time to adequately sort through, let alone encapsulate. But I think it is possible to make a few general statements.

First, sexuality in animals is complex; it goes well beyond labeling an individual animal as heterosexual or homosexual. There are actually very few species in which individuals engage exclusively in same-sex relationships. But there are plenty of species whose individuals exhibit what are considered homosexual behaviors. Beyond the obvious, these include parenting of young by same-sex pairs, and various displays of affection or bonding normally associated with mating pairs in that particular species.

Second, sexuality in animals is subjective. When you get beyond explicit sexual acts, assigning labels to animal behaviors involves a certain amount of judgment. Animals don’t identify as homosexual or heterosexual. They also don’t explain the motivations for their behaviors. If a behavior is first seen between mating pairs of opposite genders, and then later observed among same-sex pairs, does that constitute a homosexual behavior? Or is it actually a broader social behavior? Does it have to be one or the other? Think about how hard it would be to infer the significance of all the various kinds of kissing in humans just from observing, and you get a sense of the challenges and ambiguities.

Third, sexuality in animals is controversial. Most of the reports of homosexual behavior in animals are from recent studies, which has raised questions about the timing. Is it being observed now because the observers have an agenda and so want to see it? Was it under-reported in the past because it was perceived as depraved or deviant? I don’t think anyone would be surprised if a little of both were contributing factors, but there is too much evidence to dismiss it all as agenda-driven.

Hopefully, that provides a sense of the scope and complexity of studying sexual orientation in animals. But as I said, I think the real issue for Christians is how applicable all of these findings are to our understanding of human biology and human behavior. For example, from a behavioral perspective domesticated sheep may be the closest analogue of homosexual behavior in humans; approximately 10% of males are observed to mate exclusively with other males. Does anything we learn about the genetics, developmental biology, or neurobiology of sexuality in sheep have any implications for humans?

Flock of sheep

Sheep are one of the few animals where individuals have been observed to engage in exclusive same-sex mating relationships.

If one subscribes to a theory of common descent, I imagine it is fairly easy to answer ‘yes.’ After all, in that framework any genes in humans with homologues in sheep are inherited from some common ancestor, and are thus likely to have the same or similar functions. Developmental pathways will similarly share common antecedents. Of course, each species will have their own unique divergences from those common antecedents, and humans clearly have a much more complex neurobiology, but the justification for assuming a connection between animal and human results is fairly clear.

If one rejects common descent, however, the situation is probably muddier. One still can’t ignore observations about homologous genes having homologous functions across species, regardless of how one understands those homologies to have arisen. But at the same time, one can make stronger appeals to the concept of creation in the image of God as a justification for treating humans separately. Inference about similarities can in this way be restricted to only direct observation; otherwise, humans can be assumed to be unique.

Now, once again, I don’t see this forum as a place to convince anyone of a particular perspective. Rather, I’m trying to establish the terms for subsequent conversation. In addition, after thinking through this particular topic, I’ve decided that the remaining posts should focus primarily on what has been learned from human studies. I’m personally not prepared to dismiss all animal studies categorically, but I think that de-emphasizing them here will remove one potential point of contention and allow us to focus more clearly on the science.

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Andy Walsh

Andy has worn many hats in his life. He knows this is a dreadfully clichéd notion, but since it is also literally true he uses it anyway. Among his current metaphorical hats: husband of one wife, father of two elementary school students, reader of science fiction and science fact, enthusiast of contemporary symphonic music, and chief science officer. Previous metaphorical hats include: comp bio postdoc, molecular biology grad student, InterVarsity chapter president (that one came with a literal hat), music store clerk, house painter, and mosquito trapper. Among his more unique literal hats: British bobby, captain's hats (of varying levels of authenticity) of several specific vessels, a deerstalker from 221B Baker St, and a railroad engineer's cap. His monthly Science in Review is drawn from his weekly Science Corner posts -- Wednesdays, 8am (Eastern) on the Emerging Scholars Network Blog.

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    James commented on June 26, 2013 Reply

    Andy, any idea what’s the up-to-date thinking on heritability for human homosexuality? I know people have really backed off of the “gay-gene” talk of the 90s even in pro-homosexuality circles. I remember reading the heredity correlation might be 1/4 to 1/3 based on twin studies but I can’t cite that chapter and verse. In other words the heritability might be quite a bit less than say, height.

      Andy Walsh commented on June 26, 2013 Reply

      James, I started this series because I realized I didn’t have up-to-date answers to questions like that, and thought that I should. As I was organizing what I was finding, it seemed to me that we needed to get some basic assumptions on the table before we could discuss the findings and evidence. Starting with the next post, we’ll get into some of the actual findings in humans, including on questions of heritability.

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