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Evolution of Sexuality 26 June 2006

Posted by Todd in Biology, Evolution, Homosexuality, Queer Theory, Science, Sexuality.

bonobo.jpegIn a recent review, seedmagazine.com lays out the arguments of Stanford biologist Joan Roughgarden in her recent article in Science and her book of last year, Evolution’s Rainbow. “The Gay Animal Kingdom” stirs up controversy in the field of evolution by laying out Roughgarden’s basic argument that Darwin’s notion of “sexual selection” was simply wrong, as evidenced by the over 400 species of vertibrates who exhibit wide range of sexual behaviors. [As a side note, some of Roughgarden’s detractors point to the fact that she is an MTF transsexual to discredit her; but I find those arguments to be disingenuous at best and really beside the point. Roughgarden makes thorough, substantiated arguments that should be addressed on their merits.] As I read the review (full disclosure: I’ve not read Roughgarden’s original article or book, so I may misrepresent her arguments based on the review), I couldn’t help but have some pretty serious doubts as to the reliability of Roughgarden’s conclusions (I also found it problematic journalistically that the serious doubts of Roughgarden’s peers were relegated to a pargraph at the end of the article).

As a background to my objections, let me bring up some social scientific data. In a post a couple weeks ago, I laid out the basic outlines of the study of the biological origins or basis of homosexuality among humans (see Biology and Homosexuality). It is pretty clear that there is a strong biological component of same-sex attraction and behavior, but that’s only part of the story. I had mentioned on that post a work by Stephen O. Murray called Homosexualities, which is a kind of clearinghouse of anthropological and historical data about how numerous cultures around the world have organized same-sex sexuality, how the understood it, controled it and channeled in through their society. Murray argues that there have been in human history for basic patterns that overlay the specifics on the ground: age-differentiated homosexuality (that is, between younger and older individuals (e.g., ancient Greece)); gender-differentiated homosexuality (where same-sex sex is understood in terms of gender presentation of the individuals (e.g., certain Latin American cultures where a “straight” man (masculine) has penetrative sex with a “gay” man (feminine) without loss of status or aquiring a salient sexual difference)); ritual homosexuality (associated with a religious rite or practice, usually a subset of age- and gender-differentiated homosexualities (e.g., hajira in older hindu practices, which is a gender-differentiated ritual homosexuality)); and finally egalitarian homosexuality (e.g., gay and lesbian identities in contemporary U.S., and a mode of homosexuality spreading around the world right now). [I would be interested to read a similar breakdown of the ways that human beings practice opposite-sex sexuality.]

The point is that although there is ample evidence for the biology of homosexuality, the complexity and diversity of human sexual expression can only be explained by bringing the biological and the cultural together (where they belong). It is hopefully intuitively obvious to most that human beings have sex for many different reasons, as I’ve explained elsewhere before: horniness/arousal, boredom, to give pleasure, to receive pleasure, to dominate, to inflict pain, to establish social status, to reproduce, to fulfill an expected role, religious or legal duty, gender identity, power, bonding or intimacy, etc. In fact, when you think about why human beings have sex, it is rare indeed that an individual has sex because of his or her orientation; that is, being homosexually oriented or heterosexually oriented doesn’t seem to be a reason to have sex in and of itself. Further, given the many social and personal reasons that human beings actually have sex, it should be hopefully clear that, although perhaps related and overlapping, sexual orientation and sexual behavior are not the same thing. This point is vitally important when trying to see both the biological and social scientific data at the same time.

Problem 1: The review represents the evolutionary theory of sexuality as positing that homosexuality is maladaptive (it is unclear if this is just the journalist’s take or if it comes from Roughgarden). Most theorists have actually quite a bit more comlicated notions of the mechanisms of adaptability. Evolution doesn’t select against something unless it causes harm in the current environment. All organisms have “extra” features or qualities which are actually adaptively neutral. Homosexuality (or gender variance) may or may not be one of these “peacock tails”, depending on the species in question. In otherwords, homosexuality may simply be adaptively neutral in the species current environment(s).

Agreement 1: Roughgarden argues that when you study animal sexual behavior, it becomes clear that among vertebrates, and especially mammals, sexual behavior is much more than mere reproduction. Most notably, sex serves vital social roles, especially of bonding and conflict resolution, of utmost importance among social animals. This seems pretty obvious to me, given the many reasons why humans have sex. The trick, though, is to adequately connect the social and biological for any given species.

Actually, following John Dewey’s naturalism, I believe that the dichotomy of culture-biology is a false one to begin with, as the two are actually parts of the same thing and completely interconnected; culture is produced and transformed through biological pathways (e.g., sensory data, brain work, etc.) and our bodies and environments are shaped by cultural perceptions. The connection between these two is inextricable.

peacock-spread-01.jpgProblem 2: The article (Roughgarden?) just completely misrepresents the state of the field of “sexual selection” on two levels. First, the current field of evolutionary biology sees to overlapping processes occuring simultaneously, micro- and macroevolution. At the micro level, natural selection works to gradually effect change within species; at the macro level, when for whatever reason a major environmental upheaval occurs that requires adaptation or extinction, a number of processes kick in for speciation. [I’m ignoring the irritating academic pissing matches between Dawkins and Gould’s, going for what seems to be a synthesis of the evidence on mechanisms as we now have it.] The problem is with Darwin himself, who argued that sexual selection was a mechanism of perpetuating fitness as males competed for access to females; given what we now know about evolution and the wide variety of sexual behaviors in the animal kingdom, this position must be taken only provisionally, that is, it may be true in a particular species at a particular time, but isn’t a biological constant. Secondly, the idea of sexual selection in current theory has moved beyond Darwin’s early formulation. We now think of sexual selection as one of the primary methods of micro-evolution, or change within a species.

The article blows off Darwin’s peacock example as dated and no longer viable; yet the data are pretty clear that species evolve appearance and behavioral traits based on sexual preferences. Their are many features of organisms that serve only to attract mates (e.g., bower birds). This critique is given short-shrift at the end of the Seed review, which is too bad. One biologist quotes makes the point that Roughgarden has basically set up a Darwin Straw Man who doesn’t exist. And so, to me, the current understanding of sexual selection seems not at all affected by the data Roughgarden presents; I cannot see how the diversity of sexual behaviors among vertebrates eliminates the power of sexual selection. Roughgarden’s version of sexual selection is that it is a straightforward form of reproduction, which is why she wants to reject it; this however isn’t at all what sexual selection has come to mean, and indeed, sexual selection has never been used to explain the origins of homosexuality.

Agreement 2: To be fair, Roughgarden’s argument is actually that because of the centrality of heterosexual reproduction in the propogation of species, homosexuality has been seen as an anomoly or a genetic mistake by biologists. That is an issue that is important. One of Roughgarden’s projects is to prove that homosexuality is not maladaptive. As I mentioned above, homosexuality among humans is probably evolutionarily neutral. It however might be adaptive in a different species. And this brings me to problem 3.

dolphins.jpgProblem 3: Roughgarden treats “homosexuality” as a pan-species thing. This is a tricky discussion, because we must both be able to compare across species, but we must never collapse like traits in different species as being the same. So on one hand, it is highly instructive to note that across vertebrate species, homosexual behavior is virtually universal, which at the very least, gives incredible weight to the ‘naturalness’ of homosexuality. On the other hand, the relative adaptiveness or homosexuality in any given species would depend on that species’ characteristics and environment. For example, the life-partners (and sometimes threesomes) among male bottle-nose dolphins might be highly adaptive, by giving these pairs protection against predators and companionship; these males often hunt for females and copulate with females together from time to time. Among bonobos, where basically everyone has sex with everyone else, there is perhaps a strong social cohesion created, such that sex in general is highly adaptive. But does that mean that “homosexuality” write large and across cultures is adaptive? I don’t think so. Just as different human societies have organized sexuality differently, I would argue that different species do so for specific evolutionary/adaptive reasons, and that the function or adaptiveness of human homosexuality has to be judged in its own, species-specific context.

For a great run down of the careful thinking that must be done in comparing species’ sexual behaviors, I highly recommend a book I’ve actually read, Marlene Zuk’s Sex and Selection: What We Can and Can’t Learn about Sex from Animals.

Agreement 3: The easy gendering of sexual behaviors as Darwin’s Victorian context understood it have indeed been deeply assimilated into Western consciousness (although I would argue that the origins are actually Western culture itself, and not Darwin, who was simply making the basic mistake of confirmation bias in his research).

Problem 4: Roughgarden ultimately draws the incredibly problematic conclusion that human beings are actually biologically bisexual and that it is only culture that “trains” us in our sexuality. This is an idea with origins in Freud that will not die. Besides my frequent irritation with Freudian theory, my real problem here is that there is no, absolutely no, historical or biological evidence that would support this. Instead, we have evidence that some species may be biologically bisexual, most notably, bonobos. Other species may have a primary homosexuality that is interrupted for occasional breeding, like bottlenose dolphins. Human populations, as far as we can tell, have a couple things in common accross time and place: humans tend, as a species, to pair bond (the exceptions of polygyny and promiscuity speak to the complexity of our sexual behavior) and that homosexuality, although with a function in every society we know about, has always been a minority thing. It could be that our species is evolving toward a more bonobo-like existence, and it is also clear that there are social contexts wherein people can have a relative comfort with all kinds of sexual contact and behavior (cuddle pile, anyone?), but as a whole, we ultimately tend to choose a bond with another individual (a series of bonds, usually), and they tend to be heterosexual. I do believe that there are some humans who are bisexual and homosexual; but most really are biologically heterosexual. Human sexuality seems to run, with what we know now, on orientations, and its adaptability needs to be studied on its own terms.

In short, I think Roughgarden has really over-reached.

This should not prevent us from examining human sexual diversity and unweaving the connections between biology and culture; nor should it prevent us from examining the possible evolutionary functions of sexuality in humans. I don’t think this means that our tastes are determined by genes; nor do I believe that our behaviors are determined by culture. But I do believe, given what we know about sexuality (biology, evo-devo, genetics, sociology, anthropology, history) at the moment, that there are basic orientations that our cultures work with for various reasons and with varying results.



1. Lunar Quaker - 27 June 2006

This was a fascinating post, Todd. I read the Seed review, and I agree with your analysis. Roughgarden has overreached. Sometimes it takes people like Roughgarden, though, to get people thinking in new directions.

I wonder if you could comment on something. My understanding is that humans examine sexual behavior in the animal kingdom because human sexual behavior is not a reliable metric for evolutionary adaptations. In essence, isn’t that giving credence to the idea that our highly-evolved brains have given rise to behaviors that are “unnatural,” so we need to look at animals to get the true picture of what nature intended? That seems bogus to me. Human behaviors ought to be thought of as “natural” as well, shouldn’t they?

2. Lunar Quaker - 27 June 2006

Now that I think about it some more, maybe I’m committing the fallacy of attaching too much “intelligence” to evolution. I also wanted to say that I really liked your thoughts about how we shouldn’t apply a certain model for sexual traits across all species, and should keep things species-specific where appropriate.

Excellent post, Todd.

3. J. Todd Ormsbee - 29 June 2006

I do respect the work of Roughgarden and I completely understand why she’s making the analysis she is. There is something profoundly insulting about the tendency of many biologists to frame homosexuality as a “mistake” or a “maladaptation.” I also agree completely with her efforts to demonstrate the potential adaptiveness of homosexuality in various species. If it were actually maladaptive, I think it would’ve been selected against a long time ago, and we wouldn’t see it’s presence in all its forms throughout the animal kingdom.

I don’t really think that that humans look to the animal kingdom because our own sexuality is tainted by our brains. First, comparing species is a perfectly good way to gain understandings about all the species at issue and to highlight their differences.

Second, I think that presuppose that our brains have more power over our bodies and sexualities than they actually do. To be sure, humanity’s cognitive abilities allow us to trump our “impulses” (as John Dewey called all instinctual desires) because we, as a species, automatically can think about them as soon as we feel them. But there are limits to the power of our cognition, namely, that we are embodied creatures.

I don’t think that humans really do anything that is unnatural, from kinky sex to murder. We are social animals with overdeveloped senses of altruism, but we are phenotypically diverse, like all species. Especially when compared to primates, the only things that humans do that is different is that we can kill each other on such a greater scale than a baboon with a stick and sharp teeth.

John Dewey had a version of philosophical “naturalism” to which I adhere. That is basically that we are fundamentally *animals* and that our behavior and bodies are knowable scientifically, and that our social and cultural value discussions should always be in conversation with our scientific endeavors. But more to the point of Dewey’s naturalism is the way that as a species we actually produce knowledge: a physical brain that is an adaptation is in a constant transaction with the environment, and that brain’s function is adaptive, that is, to help us adapt to our environment to survive in it. That environment, among social animals like us, includes our social environment; and a great deal of our brain is occupied with helping us survive socially, not just physically. And so there is no nature “outside” of us; you cannot go to nature, you are nature. Dewey (and I agree with him) argued vehemently that the Western mind/body split, Platonic soul/body, Cartesian dualism, whatever you want to call it, was completely wrong. The mind is a product of the body and emerges in transaction with the environment.

One final comment, I think that species are both alike and different. So I don’t mean to imply that no species can be compared with another, nor that sexuality is radically species-specific. What I do mean to say is that sexuality, as an adaptive trait, evolves with the organism and so may or may not be analogous to a sexuality in another species. So comparisons must always, necessarily be also contrasts.

4. J. Todd Ormsbee - 29 June 2006

Oh, and I meant to say also that human society and culture is as natural as bonobo or lion or honey-bee sociality and culture. Social interaction and culture (the ability to pass on information from generation to generation that helps us make sense of the world and survive in it) are adaptive traits of most mammals, and many other vertebrates and even a few non-vertebrates.

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