Why Some American Parents Don't Want Sons

It's Wednesday, February eighteenth, and welcome to HigherIQ. More boys are born after wars. We've known this for a hundred and forty years. We still don't know why. But now we have something new — real data on what happens when humans can choose for themselves. And it's not what anyone predicted. Here's something that should unsettle you: the sex of a baby born in nineteen nineteen may have been determined by which soldiers were easier to shoot in nineteen seventeen. Let us explain. In eighteen eighty-three, a German scientist named Carl Düsing noticed something strange in European birth records. After wars, more boys were born. The pattern showed up after the Franco-Prussian War. It showed up after World War One. It showed up after World War Two, when American records showed the ratio of male births peak in nineteen forty-six, right as soldiers came home by the millions. The shift is subtle — the percentage of boys rises from about fifty-one point four to fifty-one point five percent. But across millions of births, that's tens of thousands of extra boys. Reproducible across countries, across conflicts, across a century of data. Scientists call it the "returning soldier effect." And after a hundred and forty years of study, we still can't fully explain it. The leading theory is genuinely strange. British Army records from World War One show that surviving soldiers were, on average, over an inch taller than those who died. Taller men were harder to hit in trenches. They were often better nourished, which meant stronger immune systems, better odds of surviving wounds and disease. And here's the connection that makes this deeply weird: taller parents are statistically more likely to have sons. We don't fully understand why — it may involve testosterone levels, it may involve something we haven't discovered yet — but the correlation is robust enough to publish. The math actually works. That one-inch height advantage among survivors could account for the entire excess of boys born in Britain during and after the war. War selected for height. Height correlates with sons. So bullets fired at the Somme rippled forward through time and tilted the sex ratio of the next generation. Your great-grandfather's height might have influenced whether your grandfather had brothers or sisters. There's a competing theory that operates on completely different mechanics. Y-chromosome sperm — the ones that make boys — are faster swimmers but less durable than X-chromosome sperm. When fertilization happens right at ovulation, the speedy Y-sperm win the race to the egg. When fertilization happens earlier in the cycle, the longer-lasting X-sperm can survive the wait while the Y-sperm die off. After wars, couples reunite and have more frequent sex. Baby booms are well documented — not just more pregnancies, but a measurable surge in birth rates. More frequent sex means more fertilizations happening at the exact moment of ovulation, which tilts the odds toward boys. The returning soldier effect might be nothing more mysterious than couples finally having enough sex to hit the fertile window precisely. Neither theory has been proven. Both could be partially true. And there's a counterexample that complicates everything: after the Iran-Iraq War, researchers documented fewer boys being born, not more. The leading explanation is that prolonged psychological stress causes women to disproportionately miscarry male fetuses, which are biologically more demanding to carry. So the "surge" of boys after most wars might not be nature producing more males — it might just be a return to baseline after years of stress-induced suppression. The honest answer is that we don't fully understand how reproduction regulates sex ratios at the population level. Nature has been running this system for millions of years, nudging outcomes through mechanisms we can observe but can't fully explain. And until recently, that's where the story ended. We watched. We measured. We theorized. But we couldn't intervene. Then we got the power to choose — and the results split the world in two. In the nineteen nineties, fertility clinics began offering preimplantation genetic testing, analyzing embryos created through IVF before transferring them to the womb. The original purpose was screening for genetic diseases — conditions like hemophilia that primarily affect boys. But the test also reveals whether an embryo is XX or XY. And once you know, you can choose. By two thousand eighteen, nearly forty-five percent of American IVF cycles included genetic testing, up from under five percent just seven years earlier. And unlike almost every other developed nation — the UK, Canada, Australia, most of Europe — America allows parents to select based on sex for any reason. No medical justification required. Some clinics advertise it openly. One estimate puts the annual revenue from elective sex selection at five hundred million dollars. So what happens when millions of humans can override nature's system? In places with deep-rooted son preference, choice became catastrophe. The economist Amartya Sen documented it first in nineteen ninety, in an essay titled "More Than One Hundred Million Women Are Missing." He'd analyzed sex ratios in China, India, and North Africa and found a massive shortfall of females — not from biology, but from discrimination. Girls receiving less food. Less medical care. And increasingly, being aborted after ultrasounds revealed their sex. By twenty ten, that number had risen to a hundred and twenty-six million missing women worldwide. At its peak, China recorded a hundred and eighteen boys born for every hundred girls — far outside the biological norm of about a hundred and five to a hundred. Some rural provinces hit a hundred and forty to a hundred. The consequences are still unfolding: tens of millions of men who will never find partners, bride prices that have soared to thirty thousand dollars, trafficking networks exploiting the imbalance. Technology didn't create son preference. It amplified it, turned cultural bias into demographic wounds that will take generations to heal. But here's where the story takes a turn nobody predicted. When researchers looked at American IVF data, they found something completely different. A ten-year study published last year tracked over five thousand cycles where parents had viable embryos of both sexes. Among those trying for their first child, only thirty-two percent chose based on sex. Most just wanted healthy. But when those same parents returned for a second child? Sixty-two percent selected based on sex. And eighty-one percent of them chose the opposite of what they already had. They weren't seeking sons. They weren't seeking daughters. They were seeking balance. One of each. The American dream of a "perfect" family. That's interesting. But here's where it gets genuinely surprising. Among first-time parents who did express a preference, a two thousand nine study found that white American parents selected female embryos seventy percent of the time. Seventy percent. Fertility doctors report the same pattern — more requests for girls than boys. A reversal of the son preference that has shaped demographics across most of recorded history. The reasons parents give are revealing. In interviews, mothers described wanting a close friendship with their child, something they believed would last into old age — and something they felt was only possible with a daughter. They talked about raising "powerful women who are going to be rock-star leaders." They used words like connection, possibility, excitement. And when asked about sons? One mother put it this way: "When I think about having a child that's a boy, it's almost a repulsion." Sit with that. Not disappointment. Not mild preference. Repulsion. At the idea of her own child. She wasn't unusual. Multiple parents described struggling to articulate any hopeful vision for a son's life — while having elaborate, optimistic fantasies for daughters. They saw girls as underdogs they could champion, futures they could shape, relationships they could nurture. They saw boys as... what, exactly? Liabilities? Risks? Something they didn't know how to raise in a world that views masculinity with suspicion? They couldn't say. They just knew they didn't want one. The same technology. The same power to choose. In one society, it produces a hundred and twenty-six million missing women. In another, it produces mothers who feel repulsion at the thought of sons. Neither outcome is nature. Both are culture — amplified by technology until we can't look away. For a hundred and forty years, we've watched nature nudge sex ratios through mechanisms we don't understand. Taller soldiers surviving battles. Sperm racing eggs. Genes doing work we can't see. The system was mysterious, but it was balanced. Roughly fifty-fifty, generation after generation, across every population on Earth. Now we can override it. And when we do, we don't reveal some universal human preference. We reveal ourselves. Our economics. Our anxieties. Our unexamined stories about which children will bring us joy and which ones we don't know how to love. In China, a hundred and twenty-six million missing women are a monument to how thoroughly a culture can devalue daughters. Centuries of patriarchal economics, encoded in birth ratios. In America, the growing preference for girls might be a monument to something else entirely — a society that's lost the script for sons. Parents who can imagine their daughters thriving, who can picture them as leaders and friends and forces in the world. But who can't imagine what a good life for a boy even looks like anymore. Both are choices. Both are data. And data, unlike opinion, doesn't care about our politics. It just tells us what we're actually doing when we think nobody's counting. The question isn't just what we're choosing. It's what our choices reveal about the futures we can still imagine — and the ones we've quietly given up on. Stay informed. Stay curious, and we'll see you tomorrow.