Photo by Cathal McNaughton / Reuters.

Isabel Caliva and her husband, Frank, had already “kicked the can down the road.” The can, in their case, was the kid conversation; the road was Caliva’s fertile years. Frank had always said he wanted lots of kids. Caliva, who was in her early 30s, thought maybe one or two would be nice, but she was mostly undecided. They had a nice life, with plenty of free time that allowed for trips to Portugal, Paris, and Hawaii.

“I wasn’t feeling the pull the same way my friends were describing,” she told me recently. “I thought, maybe this isn’t gonna be the thing for me. Maybe it’s just going to be the two of us.”

At times, she wondered if her lack of baby fever should be cause for concern. She took her worries to the Internet, where she came across a post on the Rumpus’ “Dear Sugar” advice column titled, “The Ghost Ship that Didn’t Carry Us.” The letter was from a 41-year-old man who was also on the fence about kids: “Things like quiet, free time, spontaneous travel, pockets of non-obligation,” he wrote. “I really value them.”

Cheryl Strayed, the author of the column, wrote back that each person has a life and a “sister life” they’ll never know—the “ghost ship” of the title. “The clear desire for a baby isn’t an accurate gauge for you,” she wrote. Instead, she recommended “thinking deeply about your choices and actions from the stance of your future self.” In other words, think about what you’ll regret later.

“The Rumpus post helped me understand that no matter what I chose, there was going to be a loss,” Caliva said. Her ghost ship would either be a carefree life or the experience of parenthood. “That was freeing. It changed my perspective from having to make the right choice to just deciding.”

Caliva liked the column so much she sent it to several of her friends.

* * *

The question of whether to have kids has puzzled me my entire adult life, in part because my reflexive reaction to the thought is “not again.”

There is a large age gap between me and my younger brother, and I was put in charge of minding him during many school breaks and holidays.

My brother was an easy-going preschooler. He pronounced “L”s as “W”s and wore a blanket like a Batman cape—the full “adorable kid” experience. Still, I was struck by how difficult it was to keep him entertained. I don’t possess the goofy sense of humor that charms the under-five crowd. I didn’t understand how to infuse excitement into otherwise boring activities like coloring or baking. We ended up watching a lot of TV, separately. I was so miserable that, one summer, I jumped at the chance to take a job filing papers in an office.

The experience of my teens left me feeling like parenting is, at worst, pure drudgery, and at best, feigning enthusiasm for someone who lacks a theory of mind. The problem is, I can’t tell if this is because 14-year-olds aren't meant to be full-time nannies or because I'm just not a kid person. And having one seems like a high-stakes way to find out.

In the fall of 2016, I posed the question—Why did you choose to have children?—on our reader blog, and the responses rolled in. In all my colleague Rosa Inocencio Smith and I collected and analyzed the emails from 42 readers, who were about evenly split between deciding to have kids and not to. (Caliva was one of them; she gave us permission to use her name and story.) To spoil the big takeaway, there doesn’t appear to be one “maternal instinct,” and not just because half of all pregnancies are unplanned. For some, parenthood is a hard-boiled belief; for others, it’s a switch that flips after a crisis. Other times, it’s just a feeling you get.

“People who’ve never had children seem really uptight about things that people with kids just roll with. Like, a little mess, or a muddy dog, or crumbs on the furniture,” wrote one mom named Mary. “A little softness in one's dealings is a pleasant aspiration. Kids do that to you.”

I was relieved to find that several people in the “no” camp described feeling perplexed by their peers’ drive to have babies: “It's like listening to people describe a color that I just can't see,” wrote Shanna.

The voluntarily childless do seem over-represented in our sample. Most American women—about 67 percent, according to a 2009 study by Ohio State University sociologist Sarah Hayford—decide as teenagers to have two children, and they roughly stick with that plan. Another, smaller group starts out wanting three or more kids and ends up having more than the average two; yet another segment starts out wanting two, but they wind up with fewer. Those like me are statistical freaks, making up just 4 percent of the population: We start out wanting kids … we guess? Maybe one? Our expectations decline with age, and, Hayford writes, “by their early 30s, these women expect to have no children.” (Her study was of women who were 18 in the 1980s; it’s not clear if the views of today’s women would evolve differently.)

Childlessness rose steeply from the 1970s to about 2005—it has since declined again—and Hayford found that a decline in marriage rates contributed most to that rise. Getting married can change people’s minds about having kids, she says. To some, “marriage means having children, so I’m entering this married world and taking on other things that go along with it,” Hayford said. (As one reader put it to us: “I’ve always said that I never knew I wanted children, until I knew that I wanted children with him.”)

Today, about 15 percent of women never have kids, but most of us start out agnostic. “There are not that many people who, early on, say, ‘I definitely don’t want kids,’” said Amy Blackstone, a sociologist at the University of Maine. Even the childless are more likely to start out unsure or assuming they will have kids. It’s only over time that they decide against it.

What is it that turns them against child-rearing? Freedom, according to the research. The childfree mostly cite either the freedom from child-care responsibilities, as one meta-analysis from 1987 found, or the freedom to travel, according to a 1995 book. A 2014 study that relied on 20 in-depth interviews with childfree women found that “they overwhelmingly focused on the benefits of their freedom and autonomy:”

Women desired a “get up and go” lifestyle so they could travel, “hang” with family and friends, and learn new things. They cited obtaining a higher education, focusing on careers, and retaining other adult freedoms. When women compared the benefits of a childfree life to socially prescribed benefits, they chose not to mother.

Freedom is a factor for both men and women, but the research suggests women are more concerned than men are that childbearing will hamper their careers. In a 2005 study, women were more likely to see parenting as conflicting with work, while men were more likely to say they didn’t want to make personal sacrifices. Childfree women are more likely to enter male-dominated professions and to focus on “achievement,” according to one study, and they they are more likely to earn more.

Women who don’t have kids, write Italian researchers Christian Agrillo and Cristian Nelini, “tend to understand motherhood as all-encompassing and overwhelming responsibility”—one that might interfere with their next promotion. Childless men and women might all be seeking freedom, but as Agrillo and Nelini quipped in their 2008 review paper, “the choice to be childfree gave women freedom to work and men freedom from work.”

Childless women end up just as satisfied with their lives in the end. (It’s teen moms who seem to struggle most.) However, one study—albeit an older one—found that “those wanting to be childless ... rated life as less optimistic and less loving, and also as currently somewhat less satisfying.” Just as I suspected, having a cheery disposition helps when you’re spending lots of time with people who wish barn animals could be their best friends.

Though the literature doesn’t address the issue as much, many of our readers feared not being mentally or emotionally equipped for parenthood. Some felt their anxieties or depressive episodes were incompatible with childlike bliss; others didn’t want to pass on their serious mental-health issues, such as bipolar disorder. “A kid isn’t like a potted plant that you can give to somebody else because it appears that you’re just going to kill it,” one woman wrote. (Another wrote that, precisely because she fears passing on her medical conditions, she’s considering adoption.)

A bad childhood can make a person less eager to relive it, even vicariously. A 1999 academic book about childfree men found those who had distant or abusive fathers were less interested in becoming fathers themselves. It can be hard to create a childlike utopia for someone else without a vision in your mind to work from: “I was not very happy as a child, and thinking back on childhood rarely brings me joy,” a woman named Farah wrote to us.

The reverse is also true, though: What sweeter payback is there than being a better parent than your own? “You ever wish things would’ve gone in a certain way in your past life to make you better in the now?” wrote Brandon, a father of two. “This is your chance to put in all the good you have and try to take away the bad.”

Society still judges people, especially women, who choose to remain childless. Even recent studies show that childfree people are viewed more negatively than those who have children—or are at least planning to have them.

But Blackstone, the Maine sociologist, said parents and the childfree are driven by similar desires. For instance, they both seek stronger relationships: For people with kids, it’s the parent-child bond, but for people without, “one of the very common reasons they cite is they value their relationship with their partner, and having a child will shift that relationship.”

Indeed, it was the desire to preserve a happy relationship that nudged some of our readers to decide against children. “My husband and I are happily married almost 10 years now,” one woman wrote. “I know for a fact that the happiness and huge love are due to the fact that we have the time, energy and desire to put each other first. To throw that away for a kid would be nuts.”

Others, though, saw parenthood as a way to honor either past or future relationships. “We had a good life,” wrote one mother of an adopted daughter. “Then my husband's brother died. We started to question what life was truly about, and realized that for us it could include raising a child.” One woman, who admitted to not being much of a little kid person, looked forward to befriending her children as adults. Another dreaded the deaths of her parents and, subsequently, the prospect of life without unconditional love.

* * *

According to Blackstone, the childfree and the childless both emphasized creating meaning.

For Isabel Caliva, the woman who unearthed the Rumpus column, that desire for meaning came in an unexpected way.

She first met her husband, Frank, at their college’s freshman orientation, when she was locked out of her dorm room one night. They stayed up all night talking, then dated for all four years. Post-college life took them to different cities, and they broke up. Years later, in 2010, Caliva called him out of the blue, saying “I’d love to try again.”

“I’ve been waiting for this call,” he responded. They got engaged the following year.

She had always been open with Frank about her kid-indecision, and he patiently waited as she mulled. One perfect spring day in 2014, Caliva was driving home from work near Washington, D.C., where she lives. She rolled down her windows, turned on the radio, and gazed out at the clear sky. A wave of contentment and joy washed over her.

But the elation was cut with boredom. “This is so awesome, but it’s also fleeting,” she remembers thinking. “Tomorrow I might have a hard day at work. I am always going to be chasing happiness, it’s always ephemeral.”

Some readers recalled a similar feeling of encroaching ennui: “I had a small inkling that if I did not have children, I might be self-absorbed my whole life,” wrote a woman named Virginia. “Too much self-reflection is boring after years of it, I suspected.”

Caliva likens it to the same feeling that inspires people to run marathons—a desire to know, once and for all, “that you’ve done something really big and really great.”

“I need to do something that’s bigger than me and outside myself,” she decided. “I need to take care of somebody else, and be completely selfless.”

She drove home and told Frank about her epiphany. Their son, Jack, will be two years old this year.

For childless women, though, meaning comes about in other ways. You would think that women who didn’t want children would have been bred out of the gene pool by now, since natural selection favors people who enjoy sex and, often as a result of that enjoyment, create progeny. But as Lonnie Aarssen and Stephanie Altman, two researchers at Queen’s University in Ontario, have written, modern life provides other ways for women to leave their mark, without necessarily having children.

Humans are anxious about their own deaths. To manage that anxiety, they seek to leave a legacy—often in the form of children, Aarssen explained to me recently,

“Our distant ancestors would have said, ‘I have these little people here, and I can influence the way they think,’” Aarssen said. “I can make a mini-me copy of myself, and convince them to have the same kinds of personality and drives.”

But there are other types of legacies—such as art, science, or religion—and historically, the money and influence necessary to create them belonged solely to men. Men also controlled women’s reproduction, thanks to a lack of good birth control. Thus, for millennia, women often had only one choice for making a lasting impact: reproduction. What’s more, most had to reproduce, even if they didn’t want to.

Those women might have passed down a “weak parenting drive” that essentially laid dormant until the modern age, Altman and Aarssen argue. Now that women have more rights and opportunities, the descendants of these reluctant mothers are foregoing making babies in order to make art, write books, start nonprofits and businesses, and pursue other non-kid accomplishments. Indeed, in a 2012 study they found that women who wanted fewer kids had a greater interest in a rewarding career, fame, and generating new ideas and discoveries.

As Altman and Aarssen write, some of today’s women “inherited genes from female ancestors who were not attracted to a life goal involving motherhood, but were nevertheless forced to endure it. Their descendants then—many women alive today—can now freely realize the lifestyle and life course goals that their maternal ancestors wished for, but were denied because of patriarchal subjugation.”

That might be why the college-educated today are more likely to be childless than those with high-school degrees or less. In 1992, researchers from the University of Pennsylvania asked the university’s graduating students if they planned to have or adopt kids, and 79 percent gave an unequivocal “yes.” In 2012, just 41 percent did. The number who said “probably not” grew from one to 20 percent.

“Young women today, one reason why they are less likely to plan to have or adopt kids than their forbears is that their engagement in friendship networks and professional networks is a kind of substitute for the need to create a family of one’s own,” said Stewart Friedman, an author of that study and director of the Work/Life Integration Project at the University of Pennsylvania. “Engagement in social and political networks, and work that has a positive impact on society—both of those factors are substituting for the creation of a family of one’s own.”

Aarssen said it’s possible that, if childlessness really is genetic, in coming decades the childfree movement will fizzle. Childless women simply won’t pass their genes along.

Of course, some of the works they have created along the way—including books about their childfree existences—will survive. In that way, they might pass their quirky legacies along after all, helping future couples as they kick their own cans down the road.