Photograph by Tony Wu / Nature Picture Library

Creatures of Possibility

Words by Riley Black

My transition was a crash course in biology, writes Riley Black. It shifted how I see life on Earth and made me think harder about the boundaries we create and uphold.

What’s so wrong with a male fish looking like a female? On that summer afternoon nearly two decades ago, a lifetime ago, I read the passage in biologist Adrian Forsyth’s A Natural History of Sex over again. Among bluegills, he explained, there are three forms of male fish. There are big, flashy, territorial males that try to court and mate with female fish according to standard “Look how big and strong I am” parameters, but then there are also two other types of male bluegill fish: “sneakers” and “satellites” and they both look like females. These fish, Forsyth gossips, are deceivers and experts at cuckoldry, waiting for the bigger males to do all the work of courtship before darting in at the last second to commit “genetic robbery.”


I felt bad for the fish. Bluegills, after all, are not known for their literary prowess and so a rejoinder from the freshwater fish was less than unlikely. Even as Forsyth tried to say that such fish had clearly found alternate paths required to win the reproductive lottery that provides grist for natural selection’s mill, the characterization of these fish seemed distinctly lurid and almost aghast, as if they were intentionally doing something illicit. It felt wrong. I couldn’t quite articulate why. My college biology professors talked like this all the time, about sexual dimorphism, sperm competition, selfish genes, and what comes of life’s struggle to create more life. Still, the focus on winners and losers, the masculine and the effeminate, among fish that care nothing for what PhDs have to say left me feeling unsettled. It would take me about 15 years to understand why.


I wasn’t the male I was designated to be at birth. I was a girl, no matter what I looked like, and by the time I read that passage I was still struggling through the murky depths of my dysphoria. Looking back, I felt for the fish because they were considered deceitful and conniving. They were cast as strange aberrations of nature just as transgender people were in the 90s pop culture landscape I grew up in. Modern America’s conflicted feelings about sex and gender had somehow become projected onto these little fish, and it wasn’t until I embraced my own womanhood that I started to see the connection. And it’s changed the way I see nature.


From the day I first tucked an estradiol pill under my tongue, my transition has been a biological crash course. I had only the barest outline of what to expect when I started. I’d grow breasts, my body hair would thin, and fat would start to accumulate in different parts of my body, my doctor told me. Other effects, I’d only discover in time. Two and a half years in, I started to get tired and wince at abdominal cramps—the emerging signs of my own menstrual cycle despite lacking some of the anatomy associated with periods. Any soft muscle is just as good as any other according to my hormones, it seems. Through it all, I was fascinated that I could change a few of my body’s hormone levels and that my biology knew just what to do with that new arrangement regardless of what was originally stamped on my birth certificate. I’d changed sex, and that forever changed the way I look at nature.

Our most powerful lessons about the nature of biological sex come from what we’ve traditionally deemed strange or confusing.

Riley Black

From a young age, we’re taught to see biology according to a set of defined conceptual boxes—especially sex and gender. The differences between boys and girls are ingrained early, eventually shifting into what’s presented as inviolate differences between men and women. It’s all under the banner of what Julia Serano termed “oppositional sexism,” a binary system in which two sexes are presented as being like two interlocking puzzle pieces that make one whole. Where one sex is strong, the other is weak, and both are supposed to have particular physical or behavioral tells. No surprise then that we readily project this same restrictive system onto other living things, treating almost anything beyond “big, strong males get more females” as suspect. Organisms that fall outside these rigid parameters are treated as outliers, strange cases that serve as examples of how “weird” nature is like female turkeys who behave like toms and baby alligators whose sex is unassigned until a particular temperature range determines whether they’ll be born male or female.


But I think our most powerful lessons about the nature of biological sex, beyond what we’ve made of it, come from what we’ve traditionally deemed strange or confusing.


I want to tread carefully here. It’s not my intent to distill a naturally-based “should” derived from what other species do. That’s partially because we can talk about sex, gender, and the relationship between them whereas your average bluegill or green frog cannot.


We Homo sapiens also have to grapple with the complicated connections between sex and gender. Sex is often spoken of in biological terms, but gender is a concept that is related to our beliefs about sex that varies across times, places, and cultures. We can ask each other what gender we are, but we can’t do the same for animals—even when some are tempted to talk about animals being transgender, for example, when they act differently from sex-based expectations. Instead, I believe that other species offer us a starting point to consider ourselves. When it comes to how I understand myself and my body as someone who’s altered her sex, the ways other species determine and express their sexual identities offer a starting point to question what we are so often told about ourselves.

I am not fighting against nature to be who I am. I am dancing along with the nature of my own body, bringing what I know and what I feel into closer alignment.

Riley Black

There is more variety and biological flexibility than I could possibly do justice to. The bluegills demonstrate how even fish designated as the same sex can take on varied forms. We know that under particular conditions, bluehead wrasse can quickly transform their ovary that makes eggs into a testis that generates sperm—different arrangements of what are effectively the same anatomical parts. Some reptiles, such as alligators and crocodiles, are not genetically determined to be a particular sex at fertilization. Instead, the sex of the reptilian embryos depends on the temperature the eggs develop within. The idea that in nature there are males and females genetically predestined to live as one form or the other immediately crumbles. What we’re left with is something more precious, that affects us just as much as a fish that looks different from its reproductive sex or a bird that seems to have traits of both males and females.


We all have the capacity to take on the traits of a different sex. We already know this from human development. The timing and proportions of hormones during gestation play a major role in what sex the vital records office is going to record when we greet the world. But it’s not as if biological sex is something that happens once, forever determined and locked in. Traits we think of as associated with sex vary throughout our lives based on the particulars of our biochemistry, especially the amounts of hormones like testosterone and estrogen—which we all have, just in different concentrations. We can even go a step further. Perhaps penis and vagina will always be treated as sex-based opposites in pop culture, but biologically they are really different arrangements of the same parts. That is part of what allows procedures like gender-affirming bottom surgery to work so effectively as it’s a matter of reshaping what’s common to everyone rather than construction from the bottom up.


Sometimes I feel like a much happier version of sci-fi movie experimenters that keep diaries of their bodily changes after, say, stepping into a teleporter with a fly. Especially in the first years of my hormonal changes, I excitedly wrote about changes in how I felt, shifts in my muscles and fat and other tissues, a kind of calling forth of the feminine that rested inside me since before I was born. I am not fighting against nature to be who I am. I am dancing along with the nature of my own body, bringing what I know and what I feel into closer alignment. It’s a biological gift granted to me through hundreds of millions of years of evolution, a celebration of commonality rather than holding perceived differences as more important.


Biological science is often focused on differences. That’s how we distinguish one species from another, determine what behaviors are associated with what sex among animals, and so much more. It’s certainly a utilitarian approach. But we should never mistake the systems and labels we create for reality. Terms change. Theories shift. Perspective—who is looking and from where—matters as much as what’s being observed. When it comes to sex, we have long relied on stark separations because it’s simpler to organize life that way. What’s more challenging is to wonder about what’s held in common and how shared genes, body parts, and behaviors can be modified into an incomprehensibly diverse and wonderful world of living things. We are creatures of possibility, not defined by our chromosomes or external anatomy, but rather by who we may become.

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