(Illustration: Carolyn Figel)

"A chicken," says Jacqueline Jacob, a poultry science expert with the University of Kentucky, "does not have a penis." With this choice anatomical fact clarified, the context was set for me to better understand the egg industry's greatest logistical challenge, one that is faced seconds after a chick hatches: determining its sex. Virtually every link in the supply chain for hens, from genetics to the size and color of their eggs, is measured and automated with obsessive precision. The egg industry in the United States depends on streamlined industrialized efficiency—agricultural economists call it an "egg complex"—to generate over 100 billion eggs from more than 370 million hens a year. It does so through highly consolidated operations that house, in most cases, over a million birds at a time, relying on advanced technological systems for everything from collecting to washing to grading and sorting. It's an ambitious endeavor that ranks the U.S. behind only China as the largest egg supplier in the world. Yet the most essential element in this massive and mechanized operation—figuring out if the hatched bird is biologically suited to lay eggs—relies on the vagaries of human eyesight. A chicken sexer—the industry's secret weapon—eyeballs the nearly identical genitalia of male and female hatchlings and, in an instant, makes the call.

A version of this story originally appeared in the December/January 2018 issue of Pacific Standard. (Photo: Jarren Vink/Pacific Standard)

A novice will fail to get it right half the time. A more successful sexer, a person who has (through a concentrated period of trial and error) learned to distinguish between nearly imperceptible differences in the genitals (called vents), will sex a thousand chicks an hour—one every three seconds—with 98 percent accuracy. Therein lies the difference between a viable egg industry and a backyard scratch farm, where it takes weeks to discern the sex of a chicken (usually through the maturation of obvious features such as a wattle, feather colors, and behavior).

How the accomplished chicken sexer achieves such accuracy is a riddle. According to Richard Horsey, a cognitive scientist who studies the process of chicken sexing, "If you ask the expert chicken sexers themselves, they'll tell you that in many cases they have no idea how they make their decisions." Cognitive scientists are fascinated by chicken sexing because the mechanisms behind it could be essential for better understanding the way we assess other situations and, in turn, make other decisions.

The encouraging feature of chicken sexing is that the process, although mysterious, is quickly learned. As a result, knowing what the brain does when it accurately determines the sex of a bird could soon bear on how soldiers distinguish friend from foe in combat, how doctors make accurate diagnoses, how bird watchers identify species on the wing, how scientists interpret seismic data, and even how kids learn to read. Industrial sexers are worth investigating because, as quickly trained experts who have to make split-second decisions, the way they learn to see chicken genitals might one day help clarify how the rest of us learn to see the world.

The history of vent sexing is essentially a unique history of rapid skill acquisition. After thousands of years of assuming that hatchlings were physiologically indistinguishable, the Japanese determined in the 1920s that chicken sexing could, in fact, be taught. The then-new Zen-Nippon Chick Sexing School did just that. It offered intensive two-year courses on how to discern pullets (female) from cockerels (male). By 1934, it had trained over 1,400 sexers, turning Japan into the guardian of what became the poultry industry's rarest, weirdest, and most important skill.

The central pedagogical aspect of sexing was and remains quick repetition over a focused period of time. The sexer must become proficient at immediately and unthinkingly recognizing the chickens' vent shapes, of which there are hundreds of slight variations. With intense exposure to chick genitalia (and lots of perished chicks, as it's common to squeeze them too tightly when trying to puff out their vents), Japanese students were consistently able to internalize pattern recognition and intuit rather than consciously identify the markers determining sex. Some achieved accuracy rates that were close to perfect.

By the mid-1930s, the Japanese began exporting this knowledge to the West. In 1935, a young Japanese sexer named Koichi Andoh spent five months in Yorkshire, England, teaching employees at the F&T Lumb's Hatchery his homegrown skill, turning Yorkshire into an unlikely center of chicken-sexing expertise while significantly boosting the country's poultry production.

(Illustration: Carolyn Figel)

That same year, agricultural experts from Tokyo Imperial University visited North America to teach students how to sex chicks. American students were awed and inspired. One visiting sexer wowed a classroom as he sexed 1,400 chicks in an hour with a 98 percent accuracy rate. The best anyone in the U.S. had seen before that was about 400 birds an hour with an accuracy rate of 85 percent.

The Americans quickly caught on. A poultry aficionado by the name of S. John Nitta established chicken-sexing certification programs throughout the 1940s. After learning the craft in a Japanese hatchery, Nitta founded the American Chick Sexing Association in 1938. Following the war, he placed Nisei—second-generation Japanese Americans who trained and excelled in his programs—in charge of his satellite schools. The Nisei, many fresh from the tragedy of internment, hired other Nisei. By 1950, 90 percent of the chicken sexers in the U.S. were Japanese Americans. It is not uncommon for ethnic groups to dominate certain industries, but this level of saturation was perhaps unprecedented.

Legends emerged; two Anglo Americans stood out. One was Ruby Sebree from McLeansboro, Illinois, a savant sexer with a cool head. After only weeks of training at one of Nitta's schools, she was sexing 1,100 birds an hour with a 95 percent accuracy rate. If she slowed down a bit, she could do 900 without a single error. In 1945, while working for a hatchery in Springfield, Ohio, Sebree once sexed 500,000 birds in four months (the work was seasonal then). Such machine-like achievement gradually came to be rewarded with comparatively high salaries, especially as the skill proved pivotal to the sector's industrial growth. Today, chicken sexers can start at $60,000 a year, close to double what other workers make in a hatchery.

The other noted chicken champ was Hugh Grove, an independent sexer from Oregon. He learned to sex chickens in 1937 and squeezed his last bird 63 years later. Grove was able to reach the peak of 1,500 birds an hour. He notes that, today, with the intense consolidation of the poultry industry, sexers are no longer independent agents. They are instead dependent functionaries in an industry that keeps them hidden. When I asked Pam Freeman, editor of a poultry magazine, to introduce me to a chicken sexer, she said, "I honestly don't know anyone who has met a chicken sexer."

But with the average cost of a dozen eggs under $3, be assured that they are out there, even if they are guarded like state secrets and paid like local gentry.

There are important reasons for bringing them out of the shadows. Chicken sexing reminds us that, not only are there different ways to see, but—subtle as the cues are—those ways of seeing can be quickly acquired. Studying a century of chicken sexing led the cognitive scientist Richard Horsey to reject the premise that it is a "truly gestalt phenomenon which cannot be broken down into the recognition of particular features." To the contrary, it can be divided into discrete steps and adapted to other uses.

One example that's actively being explored is seismic data. Currently, seismic data is most often presented as a complex series of vertical and horizontal slices representing the Earth's surface. Because it is notoriously difficult to interpret, even after a great deal of training, scientists are turning to chicken sexing as a model to visually rearrange seismic imagery so that accurate interpretation can be learned as rapidly as possible. The same principle holds for medical professionals interpreting mammograms. One study, stressing "the perceptual aspects of expertise," suggests that the visual perception has an odor-related parallel—one that can help better train wine connoisseurs.

The big fix to come from chicken sexing awaits. But the fact that sexing a chicken is not a totally inscrutable and incomprehensible mystery relegated to the realm of intuition, and the fact that a mode of enlightenment can be empirically understood and rapidly acquired, has the potential to push humans to envision a broad set of solutions to problems ranging from medical mysteries to data interpretation that currently elude our perceptions.

Not a bad thing to get from eggs.

A version of this story originally appeared in the December/January 2018 issue of Pacific Standard.