Leta Hollingworth was bored and frustrated. After getting married and moving with her husband to New York, she had expected to continue her career as a teacher—until she realized the city had a policy prohibiting married women from teaching. She didn't have children, and homemaking proved decidedly lacking in intellectual stimulation, so she went back to school. By 1916, she had earned a PhD in educational psychology from Columbia University.

Often remembered for her contributions to gifted education, Hollingworth also did great work in scientifically debunking commonly held misconceptions about women. Her dissertation disproved the notion that women became mentally incapacitated during their periods, and she was a vocal opponent of the "variability hypothesis," which suggested that men exhibit greater variation in psychological and physical traits than women, making the latter destined for mediocrity.

But she really began stirring things up when she published an article in the July 1916 issue of the American Journal of Sociology challenging the widespread myth of maternal desire as intense and innate in all women. "There is a strong and fervid insistence on the 'maternal instinct,' which is popularly supposed to characterize all women equally, and furnish them with an all-consuming desire for parenthood," Hollingworth wrote. "Since we possess no scientific data at all on this phase of human psychology, the most reasonable assumption is that if it were possible to obtain a quantitative measurement of maternal instinct, we should find this trait distributed among women." In other words, Hollingworth thought interest in having children naturally varied from those with "zero or negative interest," through those with a moderate amount of interest, to those whose "only vocational or personal interest lies in maternal activities."

The concept of maternal instinct had figured prominently in scientific theories since the time of Charles Darwin. Late 19th-century psychologists believed women possessed a unique need to create and care for offspring. In the late 1800s, experts attempted to use biology to shore up this theory, positing that maternal instinct was located in the female reproductive organs.

Hollingworth wasn't buying it. "There is no verifiable evidence to show that a maternal instinct exists in women of such all-consuming strength and fervor as to impel them voluntarily to seek the pain, danger, and exacting labor involved in maintaining a high birth rate. We should expect, therefore, that those in control of society would invent and employ devices for impelling women to maintain [the] birth rate."

She believed the circulation of the myth was itself one of these devices. Other ways society pressured women into having more children included the promotion of the idea that only abnormal women don't want babies; stigmatization of interests other than the maternal as dangerous, melancholy, or degrading; female sterility as grounds for divorce; limited education opportunities for women; and the widespread depiction of the "sacredness and charm of motherhood" in art, literature, and music.

Additionally, contraception was illegal and considered obscene, and dissemination of any family planning information was outlawed. Hollingworth was writing in the same year that Margaret Sanger opened the first birth control clinic in the US, which police immediately shut down.

We have a word for someone who does not eat meat, but we don't have a word for someone who does not have children.

You would think that because women in the US are now allowed to work, access equal education, and obtain birth control (for the most part) that we would have transcended this notion of motherhood-as-default. You'd hope, at the very least, that because this female psychologist called BS on the existence of maternal desire 100 years ago that our views could have progressed since then.

But our ancestors were regrettably talented at embedding these ideals into the fabric of society; they became internalized and were passed on to future generations. Fast forward 100 years from Hollingworth's article, to July 2016, and you'll find actress Jennifer Aniston in the Huffington Post lamenting "the perpetuation of this notion that women are somehow incomplete, unsuccessful, or unhappy if they're not married with children," and "how much we define a woman's value based on her marital and maternal status."

Indeed, our only words for non-parents either have negative connotations—e.g., "barren," which only denotes an inability to bear children—or merely describe a lack of something: childless, childfree. We have a word for someone who does not eat meat, but we don't have a word for someone who does not have children.

Thanks to what Hollingworth referred to as a "consistent social effort to establish as a norm the woman whose vocational proclivities are completely and 'naturally' satisfied by child-bearing, childrearing, [and] related domestic activities," mothers who seek professional fulfillment are also suspect. We are still discussing how the choice to have kids is a catch-22, vigorously debating the motherhood paradox, and perpetually pondering whether or not it's possible for women to "have it all."

One way the media continue to reinforce the social norm of motherhood is by consistently reminding women of their "ticking biological clock." In a Psychology Today article published in 2013, evolutionary psychologist Gillian Ragsdale noted that "the press is awash with warnings about delaying motherhood and the short-sighted selfishness of career-hungry women who suddenly realize it's now or never. The implication is that either these women have been suppressing their maternal drive in pursuit of other rewards or they never had any."

Ragsdale believes it's not that simple. "Many women find the decision to have a baby agonizing because they think they should just know, intuitively, whether they really want one or not. If they don't feel really driven then maybe they are not cut out for motherhood." But she explains that, just as Hollingworth hypothesized, "rather than a single, all-purpose maternal instinct... talking to women of all ages soon reveals a wide range of interest levels when it comes to having a baby."

Many women find the decision to have a baby agonizing because they think they should just know, intuitively, whether they really want one or not.

In Hollingworth's time, part of the increased pressure to procreate was borne of a eugenics movement predicated on the notion that the nation's population increase was coming from the "wrong" source: immigrants. In 1903, President Theodore Roosevelt declared Americans were committing race suicide, and urged the "best stock" to procreate: the Anglo-Saxon, American-born middle class. He compared a women's obligation to reproduce to that of a man's duty of military service, calling women who avoided their duty vicious, cold, and shallow-hearted.

In her book Barren in the Promised Land, historian Elaine Tyler May writes that Hollingworth was "one of the few professionals in any field to question the existence of the maternal instinct," and that her ideas "fit popular sentiment and behavior more closely than did those of the eugenicists."

Later, during the post-World War II era, came the baby boom, when nearly everyone was having children. May says during this time, the childless "faced both pity and scorn, taunted as immature at best and subversive at worst." It wasn't until the "powerful ideology of domesticity gave way to the sexual revolution" that "a new emphasis on individual choice and a lessening of social pressures to conform to the ideal of a nuclear family" emerged.

May believes this should have meant that the bad old days were over, and life with or without children ought to be perfectly acceptable. But that's not how things played out, leaving May to ponder why there is "this lingering—even heightening—obsession" with reproduction.

One reason may be the rise of effective contraception and reproductive technology. "Ironically, the increasing legitimacy attached to a variety of reproductive options, along with the promise of technological fixes to help achieve individual goals, has increased pressures and heightened the social stakes in reproduction," May writes. "As a result, Americans have become more, not less, preoccupied with their own reproductive fates—and everyone else's."