Those Freemartin Girls


The first time I met my patronus, I was wearing full-body overalls, my arm still stinging from being wedged up another cow’s sphincter. She was a small yearling calf with a blue tag on her ear, and I asked the veterinarian I was shadowing what the tag signified.

“Now that,” Dr. Akers said, “is a Freemartin. Sad little thing. She had a male twin, who poisoned her in the womb. She’ll be infertile for life. Next month she’ll be sold with the steers.” Steers were meat cattle; future burgers.

I stared at the yearling calf, her long lashes around her deep brown eyes. If I’d spent more than two weeks around cows, I’d have seen her wide-spaced eyes and oddly slender hips. Suddenly aware of my own manly build, I reached out and rubbed the white star on her forehead. She butted up against my touch, knocking me slightly off-kilter. My boots stuck in the manured walk and I flailed. By the time I caught my balance, Dr. Akers had moved on.

I couldn’t shake the image of her slightly dull, sweet expression, or the knowledge that she was both female and not. That night, when I’d scraped my boots clean and showered twice, I thought about calling my twin brother. We didn’t talk often; there was too much history we wanted to forget. I wanted to joke with him, tell him he’d poisoned me in the womb, that my woes were his fault. He would tell me that it had just been his way of getting back at me for eating up all the nutrients.

Instead, I stared into the mirror, humorless. Dr. Akers had assured me that humans couldn’t experience freemartinism. All the same, I wondered if a Brave New World life1 had been forced upon me. I’d been obsessed with my boyishness long before I took a break from my liberal arts degree to have a summer fling with ranching. Perhaps my wide shoulders and low voice weren’t just quirks, but something gone wrong before I’d even glimpsed the world.

All mammals begin life as mostly female.2 Activation and production of male hormones are necessary to start the differentiation process. These hormones are generally two types: androgens, such as testosterone, that promote male traits and sex organs; and anti-Müllerian hormone, which suppresses female traits. Unfortunately for dairy farmers, cattle twins share a placenta, which means they have no barrier to prevent the male’s hormone bath from changing the female twin into a chimera, neither wholly female or male.3

As a general rule, intersex cattle are not particularly good for the dairy business. Like most male calves, those that make it to adulthood are best sold to ranchers for their meat. There is always a slim chance that a freemartin will develop into a fertile, milk-bearing adult and it is this hope that most conflicts a dairy farmer. They must decide if the chance of a healthy calf will outweigh the damage twinning works on the mother.4 At a small dairy, without the resources to deal with that kind of risk, aborting the twins is often the only reasonable option.

Most other mammals have no risk of freemartinism. Since human twins each ride out the pregnancy in their own placenta, they are spared from the majority of their twin’s chemical bath. Yet, despite early evidence toward healthy male-female twin sets, there is increasing consensus that twins do affect each other in utero. This twin testosterone transfer hypothesis means that human twins might have a little freemartinism in them after all.


By all accounts, both my brother and I suffered from our time in the womb. Crammed against each other, we shifted late in the pregnancy to an abnormal arrangement—my brother sitting upon my back, my face pressed against my mother’s spine, his twisted down against his body. I was born with a crushed, flat nose and lordosis5 that would plague me for life; he was born underweight. Those months we shared should have bonded us permanently together,6 but I’ve never felt privy to my brother’s deepest thoughts or feelings, and we share little in our adulthood.

Then again, perhaps puberty is to blame for that. Mine rolled in late and brought with it all of the usual girl worries: perhaps my body was wrong, perhaps I was wrong, why didn’t boys fawn over me like that other girl? I couldn’t help but look at my tan, lithe brother and wonder why I had gotten the muscles and width and athletic ability. I’d have much preferred his straight hair and slender body instead of mine. While my friends dieted and tried contacts, I bruised my ribs with a waist-training belt and gave up wearing skirts that showed my legs.

I knew enough to hide my desire to feminize my body. Despite the ultra-conservative community that my family belonged to, I’d grown up with powerful, strong female role models. Sunday school taught me that women needed to be passionless paragons of virtue, but I’d learned every curse word I knew from my mother. The women I admired were sarcastic and bold and could do any work a man could. I learned to call myself a feminist and my brothers started calling me “butch.” Pastels and belly shirts were in, but I was busy wearing knee-high combat boots and flak jackets, flaunting the strength I was secretly ashamed of.

I never told anyone how much it rankled when I would be mistaken for a guy in the supermarket, or have the guy I was crushing on confide in me because, “Girls, right?” I got defensive around guys when they focused on my friends, boiling in resentment toward myself. My friends called guys assholes and sympathized when I broke down and admitted to one crush or another, but I knew the truth: what straight guy would be interested in a girl that could arm-wrestle them to the floor?


Of course, there have always been women who were physically stronger than most men. Human dimorphism is relatively small; men and women are about the same size and behave in similar ways. In order to find differences, a researcher needs to focus on statistical likelihood, patterns, and minute physical alterations. It involves measuring such factors as the length difference between the second and fourth finger, or the size of teeth. Vocabulary words are counted and tallied and block-matching exercises are timed and scored. All those tests build up to reveal significant changes.

Behavior, the most fluid trait, is nearly impossible to link to genetic qualities at all. Classic autism is one exception: boys are much more likely to be on the spectrum, regardless of upbringing. Yet, boys with a female twin are much less likely to develop autism, especially compared to boys with a male twin. Girls, much more likely to develop eating disorders, are less likely to develop one if they have a male twin, regardless of upbringing or social circumstances.7

Mentally, the effects are even clearer. Girls with a male twin score more like boys in a number of cognitive tests, from selective hearing to spatial reasoning.8 Physically, there are a slew of effects that are the clearer evidence of effect. Everything from brain, tooth and finger size to right/left-handedness is masculinized in baby girls with a male twin. Yet, the most telling statistic comes not from measurement of bodies, but rather long-term effects. Freemartin girls are fifteen percent less likely to marry, and twenty-five percent less likely to have children.9 Indeed, research into other mammals that experience Testosterone Transfer have demonstrated that it isn’t just a physical trait. Somehow, males can sense the masculinization of these females and are repulsed by it.10

Humans are less driven by instinct than animals; our impulses are moderated by socialization and education and intelligence. Though my twin brother dated intermittently and all of my friends had found someone to cuddle in the movie theater, I entered adulthood without any experience of puppy love. I reassured myself with each year that I only needed to move away from my hyper-religious community, or find more mature guys, or finish my school first, or dress sluttier, or start drinking more. At twenty-six, still without a relationship lasting longer than a one night stand, my twin announced his engagement. On his off-hours during his military deployment, he’d found love online. I should have been ecstatic, but resentment is a hard crutch to give up.

Visiting home that winter, I sat at the counter watching my mother prepare the next day’s dinner. Flour dusted her cheek as she stared at me.

“What do you mean, you probably aren’t ever going to have kids?” In my parents’ world, the announcement was tantamount to blasphemy.

I shrugged, unwilling to admit to the lifetime of romantic disappointment that she suspected, unable to express the hopelessness that left me sobbing when I passed the elementary school by my apartment, or the desperation that peppered my online dating profiles. “I just keep thinking being tied down like that would murder my career.” At that point in time my career was waitressing part time and a few articles written up for bloggers. She didn’t call me out on that.

“What about kids? You would be a great mother. Don’t you want that life? You don’t have to find a guy for that. You could adopt or foster.”

I stared down at the granite countertop. Technically her words were true; I just couldn’t imagine having kids without a partner by my side, and I had stopped imagining there was a partner out there for me. “It just doesn’t seem to fit with what I want right now.”

She stared at me and I could have sworn that she knew my secret desperation. “That’s fair, hon, but what if things change? What if you wish you’d had kids later?”

New information constantly changes the scientific landscape and scientific studies are rarely as simple as the news would like us to imagine them. Though some testosterone slides its way toward female twins in utero, the long-term effects are hard to track or understand. No one has managed to find out whether the physical and mental effects of testosterone continue to affect female twins past puberty, though several studies are in the works.11 For now, we simply do not know. It is easy to see masculine patterns in my life and forget that I come from a long line of big-boned, powerful women; that hormones might not be the only factor that led me to this life.

Emotional fallout isn’t always clear-cut either. Meeting that freemartin was a revelation for me: justification for my off-gender mannerisms and body, another creature bridging the space between male and female.

Maybe it is better I live in a gray area, that I must treat male and female traits as more of a spectrum than a dichotomy. After all, no matter how simple freemartinism might make my gender identity, claiming it dismisses a lifetime of feminist, gender-queer thought. I can hardly argue gender isn’t tied to physical sex when I am blaming some of my best qualities—exceptional spatial reasoning, selective hearing, strong hands—as inherited traits from my brother. I can hardly claim that women can accomplish anything a man can while crediting my own strength to a freak genetic event.

In the years since my brother’s wedding, a lot has changed. I’ve dated and had the galling realization that perhaps my years of loneliness stemmed from my own unattractive qualities. I’ve dated other, less broken individuals who taught me that my masculine body could be womanly, too. Life has rooted my liberal leanings in compassion and empathy rather than anger and resentment. There are still many years ahead, where the possibilities change with every passing day. Perhaps I might fly in the face of statistical likelihood and have children, raising them to appreciate gender and sex as something more complicated than blue and pink.

Or perhaps I will adopt a little jersey Freemartin cow to keep me company in my old age. We do, after all, have a lot in common.


Image credits: feature image, image 1, image 2, image 3.


1. Brave New World by Aldous Huxley envisioned a world in which in-utero chemical sterilization of female babies was used as social and genetic control.

2. Mauk, Ben. 2013. “Why Do Men Have Nipples?” LiveScience. TechMedia Network. February 1.

3. Lyon, Laurie Ann. 2007. “What Is A Freemartin.” The Cattle Site. 5M. March 10.

4. Fricke, P.m. 2001. “Twinning in Dairy Cattle.” The Professional Animal Scientist 17 (2): 61–67. doi:10.15232/s1080-7446(15)31599-0.

5. Also known as swayback, lordosis is an unnatural spine curvature. Untreated, it can result in pigeon-footedness, difficulty sitting or standing straight, and lower back pain.

6. “The Bond Between Twins.” 2016. Twin Pregnancy And Beyond. Accessed July 8.

7. Cohen-Bendahan, C.C.C., Van de Beek,C., Berenbaum, S.A., (2005). Prenatal sex hormone effects on child and adult sex-typed behavior: methods and findings. Neuroscience & Biobehavioral Reviews, Volume 29, Issue 2. 353-384.

8. Vuoksimaa, E., Kaprio, J., Kremen, W. S., Hokkanen, L., Viken, R. J., Tuulio-Henriksson, A., & Rose, R. J. (2010). “Having a Male Co-Twin Masculinizes Mental Rotation Performance in Females.” Psychological Science, 21(8), 1069–1071.

9. Lummaa, V., Pettay, J. E., & Russell, A. F. (2007). Male twins reduce fitness of female co-twins in humans. Proceedings of the National Academy of Sciences of the United States of America, 104(26), 10915–10920.

10. Vom Saal, F. S. 1978. “In Utero Proximity of Female Mouse Fetuses to Males: Effect on Reproductive Performance during Later Life.” Biology of Reproduction 19 (4): 842–53. http://doi:10.1095/biolreprod19.4.842.

11. Cohen-Bendahan, C.C.C., Buitelaar, J.K., Van Goozen S.H.M., Orlebeke, J.F., Cohen-Kettenis, P.T., (2005) Is there an effect of prenatal testosterone on aggression and other behavioral traits? A study comparing same-sex and opposite-sex twin girls. Hormones and Behavior, Volume 47, Issue 2. 230-237,

Kathryn Collins's essays and poetry have been published in Burner Mag, Rational Faiths, Vocal Media, and Bank Heavy Press. She recently received her MA in Professional Fiction Writing from the University of Denver, and currently works as a librarian. After a long period as an expat in Germany, Israel, and Australia, she has returned home to the Rocky Mountains of Colorado. More from this author →