On Oct. 31, 1926, Charles Vance Millar, a well-known and wealthy Canadian lawyer, died at age 73. Halloween was a fitting day for him to go; Millar loved practical jokes and spent far too much time doing silly things like dropping dollar bills on the sidewalk and then hiding to see who would pick them up. But that was just a warm-up. In death, Millar unleashed his biggest prank ever — a last will and testament that was basically a giant social experiment. By promising a vast sum of money to the Toronto family that could have the most babies in a 10-year period, Millar set off a race to give birth the moment he died.

Millar described his will as “necessarily uncommon and capricious” because he had “no dependents or near relations.” What Millar lacked in heirs, though, he made up for in cash and property. In addition to his work as a lawyer, Millar amassed a net worth of more than $10 million (in today’s Canadian dollars) through a series of investments, including the property that would eventually be used for the Detroit-Windsor Tunnel, one of the busiest crossings between the United States and Canada. He wanted to give that wealth away.

But he wanted to do it in as roguish a way as possible. Millar started off by giving shares in a jockey club to gambling opponents and shares in a brewery to teetotalling religious leaders. Then he left his house in Jamaica to three men who hated one another, on the condition that they own it together. But those were just a prelude to the big finish. In clause 10, Millar revealed a biology and math challenge that would change the lives of dozens of Toronto families. The remainder of his fortune — about $9 million — would be bequeathed a decade later to “the mother who has since my death given birth in Toronto to the greatest number of children as shown by the registrations under the Vital Statistics Act.” If there were a tie, he wanted his fortune to be divided equally among the winners.

Millar probably thought he was being clever; after all, childless people aren’t often responsible for baby booms. He may have even been making a wry statement in support of birth control — he was known to think that using contraception shouldn’t be the taboo it was. But he probably wasn’t thinking about what would happen to the losers and all the new mouths they would have to feed, and he certainly wasn’t thinking about the Great Depression, which would soon envelop Canada and the rest of the world. That historical coincidence drove an ever-larger and ever-more-desperate group of women to try to win Millar’s fortune. Soon the local papers, led by the Toronto Daily Star and The Evening Telegram, anointed it the Stork Derby.

As the years passed, the Derby faded into history, leaving behind just enough scraps for Snopes-verified chain emails. In 1994, a graduate student at Dalhousie University in Halifax, Nova Scotia, named Elizabeth Wilton wrote her master’s thesis on the Derby and for the first time dug up and compiled the relevant court records. Wilton’s thesis was eventually used as source material for an overwrought Canadian TV drama, but many of the details she unearthed are a previously untold gold mine for those of us trying to figure out how an extreme fertility contest could have played out.

In its most ruthless interpretation, the Stork Derby was a mathematical and biological challenge for the participating families. How could they maximize the number of babies they had?

For the past 170 years or so, much of the industrialized world has undergone what researchers call the historical fertility transition, as economic incentives and labor practices changed to favor smaller families. The fertility rate has dropped precipitously during that time. Families went from having five or six kids in the 1800s to only about two today. Canada’s current total fertility rate is only 1.59, well below replacement level. (The rate in the U.S. is 1.87.) In 1926, Canadian families averaged 3.36 children each. But when the Depression set in, the fertility rate dropped, to 2.80 by 1934 — much faster than the historical fertility transition would have predicted. According to University of Minnesota economist Larry Jones, fertility rates dropped more during the Depression than during any other era in history, which is why he refers to those years as the “Baby Bust.”

If a woman could have had a baby the day the contest was announced and every nine months for the next decade, she would have ended up with 14 babies. But, of course, human reproduction doesn’t work that way. As Jane Frederick, medical director of HRC Fertility, a clinic in Orange County, California, explained, conception is difficult, especially for new mothers. The likelihood of getting pregnant again depends on “if she breastfeeds and how much time her uterus is given to recover,” Frederick said. Many Derby contestants presumably weren’t breastfeeding regularly, as lactation often prevents ovulation; one study found that it’s as effective as condom usage in preventing pregnancy for the first six months postpartum. And Stork Derby contestants weren’t resting their uteri for several months after each birth — many had two babies within a 12-month span. That meant the likelihood of miscarriage was higher.

Even if the uterus has time to recover, 10 percent to 20 percent of known pregnancies end in miscarriages (and even more conceptions spontaneously abort before the woman knows she’s pregnant). Frederick emphasized that most of these miscarriages, especially among younger women, occur randomly. “The most common reason is genetic problems with the embryo; there’s not enough genetic information for it to go full term,” she said.

When I asked Frederick how many babies a woman who was trying to maximize her fertility could expect to have in a decade without using modern fertility treatments, she said four to five if the woman was breastfeeding and up to seven if not.

Very few articles focused on the toll that the contest had on the desperately poor families trying to win. One referred to Lillian Kenny as a contender before noting that one of her babies had recently died from rat bites.

Of course, there’s a shortcut to having lots of babies — have more of them at once. Nadya Suleman, for example, had 14 kids (including one set of octuplets) in just nine years, from 2001 to 2009, using in vitro fertilization. Back in the 1930s, though, there was no IVF and no Clomid or other fertility-increasing drugs. That meant that not only were there no chemical ways to increase the odds of getting pregnant, but women also were less likely to have twins (or triplets) than women are today. Based on pictures and newspaper articles from the time, very few of the Derby contenders appeared to have had multiple births.

So what techniques could the Derby participants have used to increase their fertility? Besides mothers skipping breastfeeding, there were a few other ways to optimize the chances of getting pregnant, Frederick said. “Back in the 1920s, they didn’t know what the hormones were, but they did know that women cycled,” Frederick said. Shahin Ghadir, a fertility specialist at the Southern California Reproductive Center, said this information would have given the families a crude sense of when they were most fertile. As for the men in the Derby families, Frederick said they could have increased their fertility by abstaining from sex and masturbation for the five days before intercourse. But even if a family had done everything it could to conceive as fast as possible, it comes down to whether the people trying to have a baby are a particularly fertile combination, Frederick said.

It’s unknown how many families decided to try to win Millar’s fortune. While there were a few mentions in the press early on, news coverage of the Derby didn’t really pick up until 1932, when the Ontario government tried to have the will nullified and the money given to the University of Toronto. After a huge public outcry — the Toronto Daily Star accused the government of resorting to “communism in the raw” — the government’s claim was withdrawn. At that point, several other women seem to have realized that their family size put them in contention and started to compete as well. By the deadline in 1936, more than two dozen Toronto families had welcomed at least eight babies during the previous decade.

The Stork Derby eventually became a huge news story, perhaps since it provided an outlet from the miseries of the Depression. Those miseries were manifold. The Depression hit Canada almost as hard as it hit the United States. Unemployment hit 19 percent. Total earnings in Toronto’s province dropped 38.5 percent from 1929 to 1933. By 1935, more than 25 percent of Toronto families relied on government relief.

Many of the major Canadian papers covered the intricacies of the Derby, from new births among the leading families to the courtroom machinations of the Millar relatives as they aimed to stop the circus and keep the cash for themselves. Very few articles, though, focused on the toll that the contest would have on the desperately poor families trying to win. Newsweek, for example, first referred to participant Lillian Kenny as a contender for the Derby before noting that one of her babies had recently died from rat bites while living in ghastly poverty.

Ten years after Millar’s death, 32 lawyers showed up to an initial hearing to claim a share of the fortune for the families they represented. After some quick record scanning, though, the presiding judge, William Middleton, cleared out everyone who didn’t have at least nine kids younger than 10. That left six families.

But some mothers who had more than nine kids still weren’t allowed a shot at the prize. Pauline Clarke was one of them; she had 10 children within the timeline — the first five with her former husband and the second five with a different man, one she lived with after her separation from her husband. Middleton was not impressed. “‘Children,’ when used in any testamentary document, always means legitimate children,” he wrote in his judgment. Instead of $9 million, Clarke was eventually given a settlement of just over $200,000, and that came only after a lengthy lawsuit.

As for the Kenny family, it eventually settled for the same amount that Clarke did. Although Lillian Kenny gave birth to 11 children, her claim was dismissed on the grounds that three of the babies were stillborn. “A child born dead is not in truth a child,” Middleton wrote. “It was that which might have been a child.” With that, three of Kenny’s babies were scratched from the ledger. The youngest was named Charles Vance Millar Kenny, after his would-be benefactor.

Four other families with nine young children — the Timlecks, the Nagles, the Smiths and the MacLeans — were each awarded the equivalent of about $2 million. While she was in the midst of the Derby, Lucy Timleck took a moment to tell a reporter that raising a big family isn’t easy. “I think birth control is a wonderful thing,” she said in an article called “‘Dark Horse’ in ‘Stork Derby’ Now Believes in Birth Control.” “I am sorry, in one way, that birth control information wasn’t available years ago. I know mothers who would have welcomed such knowledge.”

Kevin Timleck, 52, is the son of Edward Timleck, who was Lucy’s youngest child. Kevin lives in Vancouver and told me that he has more than 100 first cousins spread out across the country. While many of his relatives have kept up the Timleck Irish Catholic tradition of having large families, Kevin has only two children. Why? “There’s no money involved in it,” he said.