Spec Tech: Born This Way (Thoughts on Sex, Genetic Determinism, and James Tiptree, Jr.)
I first read James Tiptree, Jr.’s beautiful story, “Love Is the Plan the Plan Is Death” back when I was a teenager and it has remained with me ever since, a mental touchstone, a reminder of the wonders that can be accomplished in just a few thousand words.
It is a story of love, the romance of Moggadeet for his adored Lilliloo. It is a story of discovery, as the life cycle of his alien species is gradually revealed to Moggadeet who, much as he tries to escape from his instinctual drives, is ever in thrall to them. It is also a story of tragedy, because the climate in which Moggadeet lives is changing, yet he and his kind cannot adapt due to their instinctual drives. Moggadeet experiences the ecstasies of love, but is aware that these will also prove to be the death of his species.
Genetic determinism is at the heart of “Love Is the Plan the Plan Is Death,” describing as it does a species so beholden to instinct and its sexual drives that it cannot adapt to a changing world. I want to use this story as a jumping off point to consider the significance of genes in controlling sexual desire. This is a topic that continues to pop up in the media, particularly in reference to ‘gay genes’ and what controls whether humans are attracted to the same or the opposite sex.
Let’s start with mice. Mice are not humans—not by a long shot, or at least by about 75 million years of evolution—but they are mammals and they also have a remarkably similar suite of genes to those found in humans. Moreover, the ability to knock out genes in mice has allowed for the identification of genes that dramatically affect their sexuality. These genes often receive media attention, a common assumption being that they may tell us something about human sexual behavior. It pays to be skeptical of such claims, but these studies do reveal the plasticity of the sexual response and how genes can control this response in some species. So, three genes and what happens when they are knocked out in mice:
- Increased sexual persistence of males that lack the gene nNOS for neuronal nitric oxide synthase. Nitric oxide is a gaseous signaling compound, which besides regulating blood vessel constriction (think Viagra), also serves as a neurotransmitter in emotion-regulating regions of the brain. Mice that are unable to make nitric oxide in their brains are overly aggressive, with male mice often fighting to the death. In addition, the male mice attempt to copulate with female mice even when the females are not in estrus and vocally and physically reject the males.
- Bisexual behavior of male and female mice that lack the gene Trpc2, which encodes a protein needed for perception of pheromones. Male mice lacking this gene cannot differentiate males from females and attempt sexual and courtship behaviors with both male and female mice. Interestingly, female mice lacking Trpc2 act like the bisexual males (rather than bisexual females), displaying male-like courtship behaviors to male or female mice.
- Lesbianism in female mice that lack the gene FucM, which encodes a gene that may affect the availability of estrogen. To be more exact these females behave sexually like male mice, and now display male-like courtship behaviors to female mice.
What about in humans? Would we see the same behaviors if we knocked out the human equivalents of nNOS, Trpc2, and FucM? The simple answer is no. Just because we have genes similar to those found in mice does not mean that we make use of these genes in an identical manner. For example, we don’t rely to such an extreme on smell in determining whether another member of our species is male or female, and so knocking out a gene affecting our pheromone recognition wouldn’t curtail our ability to discriminate male from female. This is not to say that pheromones and other hormones don’t play a role in human sexuality, but these roles are more nuanced than in mice, and so mutations in these genes will have more nuanced effects on our behavior.
The complexity of factors underlying human sexuality becomes apparent in studies aimed at determining the basis for homosexuality. Genetic studies in humans are primarily limited to studies of identical twins. These studies indicate that genetic factors explain about 20-40% of their sexual orientation; note that these genetic factors are likely to involve many genes, not a single ‘gay gene.’ The twins shared environment (e.g. family and societal attitudes) accounts for 0-20% in their sexual orientation, so what your family thinks doesn’t affect your sexual orientation much at all. In contrast, unique aspects of a twin’s environment (e.g. anything from individual aspects of the prenatal environment and childbirth, to accidents and disease, to friendships, to sexual experiences) account for a whopping 60% or more in their sexual orientation.
What often gets left out of discussions on genetic effects, and which may explain some of the variability found in these studies on sexual orientation, is that genes don’t act independently from the environment. In fact, even the scientific concept of genetic determinism takes into account the environmental conditions. The influence of the environment on genetic effects can be readily understood by considering how a pine tree will grow to hundreds of feet in height in Yosemite Valley, but to only a few gnarled feet in height up near the timberline. Translated to humans and their sexuality, this suggests that the same genetic allele can have little to no effect on one individual’s sexual orientation but a significant effect on another’s, all dependent on the environment in which each individual finds itself. Significantly, every human has experienced their own unique environment, and so their sexuality has been built on a unique interplay of genetic and environmental circumstances.
Now to return full circle, back to the beginning of this column and Tiptree’s story, “Love Is the Plan the Plan Is Death.” For me, one reason the story works so well is because Tiptree has a clear idea on the limits of genetic determinism. First, her alien species is primitive, their life cycle driven by instinctual desires over which they have little to no control. It is for this reason that she wrote her story in the purple-prose style of 1920’s pornography (“How our bodies moved in our first weaving song! I feel it now, I melt with excitement! How I wove the silk about you, tying each tiny limb, making you perfectly helpless.”). The genetic element reminds me of, and was perhaps inspired by, the long, dangerous swim of adult salmon back to their original spawning grounds, and how their ability to procreate can be destroyed by something as simple as a dammed up river. Salmon are just as much slaves to their sexual drives as the aliens in Tiptree’s story.
But, significantly, Tiptree also gave her alien narrator Moggadeet the rudimentary ability to learn, to discover the trap into which he is walking, even though he can do nothing to prevent it (“To learn, my Lilliloo! That is important. Only we black ones have a time to learn—the Old One said it.”). The alien’s ability to learn does not exist in a vacuum, and Tiptree also posits interplays between learning and the environment that, in the end, add even more pathos to the situation. Moggadeet’s primitive intelligence, and our identification with him and deeper understanding of his plight, is what elevates the story from the scientific curiosity of an alien life-cycle to a world-encompassing romantic tragedy.
1. HER SMOKE ROSE UP FOREVER. A readily available selection of Tiptree’s short stories that includes “Love Is the Plan the Plan Is Death.”
2. JAMES TIPTREE, JR.: THE DOUBLE LIFE OF ALICE B. SHELDON, by Julie Phillips. A fine biography of this remarkable woman.
This month’s column was inspired by (1) a student, Toan Do, who interviewed me as part of a project on the social implications of finding a gene for homosexuality; (2) discussions with Matthew Cheney, who maintains the award-winning blog The Mumpsimus; and (3) a panel on biological determinism at this year’s Readercon that I unfortunately had to bow out of when I came down with the flu.