Gillian Thomas is the author of the new book " Because of Sex " and an attorney at the ACLU's Women's Rights Project. The opinions expressed in this commentary are hers.

(CNN) The generational divide among women as to whether Hillary Clinton's gender should determine their vote has revived the time-worn question: Should gender even matter when deciding who should hold the highest job in the land?

However one answers that question, it's worth pausing to remember how recently it was unthinkable that the presidency was a job for a woman at all.

A single statute paved much of the way from there to here. Title VII of the Civil Rights Act of 1964, a landmark moment in African Americans' struggle for equality, also was a watershed for working women.

The law bans on-the-job discrimination because of race, national origin, color and religion; at the last minute, Congress amended it to ban sex discrimination, too.

At the time, women's access to the workforce was regulated at the state level, and those " protective " laws operated to keep women out of the best-paying jobs -- mainly those deemed too strenuous or dangerous -- rather than facilitate their entry into them.

Title VII required that women enjoy equal "terms, conditions and privileges of employment" as men and nullified such statutes.

The 'bunny problem'

Initial public response to the statute ranged from puzzlement to indifference to outright derision. News accounts jovially denounced the law as creating a "bunny problem" -- as in, would the Playboy Club now have to hire men as bunnies?

Even the early leadership of the U.S. Equal Employment Opportunity Commission, the agency charged with enforcing Title VII, scoffed at its impact. One of its early executive directors opined to reporters that "no man should be required to have a male secretary."

A tireless cadre of mostly female lawyers at the EEOC eventually overcame this resistance, and the agency became a powerful advocate for women workers. In the 52 years since the law's passage, though, Title VII's mandate -- and by extension, what we understand today to be women's rights on the job -- chiefly has been shaped by the favorable court decisions in lawsuits brought by tenacious individual women. In the process, they opened the floodgates for women's entry into all sectors of the nation's workforce.

In 1964, fewer than half of American women worked outside of the home, and roughly 40% of them had children ; today, nearly 60% of women work, as do nearly three-quarters of all mothers with children younger than 18.

Many of the earliest Title VII lawsuits challenged the notion that certain jobs were "for men only," a fact reflected in newspapers' separation of "help wanted" ads by gender, and rooted in a century of Supreme Court rulings that had barred women from practicing law or working as bartenders , for instance, or working jobs requiring long hours

In the early 1970s, Kim Rawlinson sued the state of Alabama to win employment as a prison guard. Rawlinson's case went all the way to the Supreme Court and resulted in a decision that outlawed employers' use of height and weight minimums, which functioned to disproportionately screen out women applicants, including the 115-pound Rawlinson, without improving law enforcement.

Today's female police officers, firefighters, construction workers and others doing hazardous, physical work, while still too few, are on the job because of this and related interpretations of Title VII; the law forbids employers from relying on stereotypes about women's aptitudes. (In rarer cases, men also have used Title VII successfully sued to gain access to historically "feminine" jobs, such as flight attendant.)

But as any woman who's dodged the gropes and leers of co-workers can tell you, you don't need to see a sign saying "no women allowed" to know you're not welcome on the job.

When sexual harassment was finally recognized

It took 20 years after Title VII's passage for the Supreme Court to recognize that sexual harassment wasn't just clumsy courting but rather a form of discrimination. A young assistant branch manager at a Washington, D.C., bank, Mechelle Vinson, sued after enduring more than three years of sexual abuse at the hands of her boss. Because the harassment hadn't resulted in Vinson's losing her job, the bank argued that nothing illegal had occurred. The court disagreed.

Drawing on the precedent that already had found racial harassment a breach of Title VII's guarantees, Chief Justice William Rehnquist wrote , "Surely, a requirement that a man or woman run a gauntlet of sexual abuse in return for the privilege of being allowed to work and make a living can be as demeaning and disconcerting as the harshest of racial epithets."

Women's identities as mothers had long been used to limit their job options, and Title VII made those practices illegal, too.

In the very first Title VII case decided by the Supreme Court in 1971, Ida Phillips -- a mother of seven from Jacksonville, Florida -- successfully challenged missile manufacturer Martin Marietta's policy of refusing to hire for assembly line jobs women, but not men, who had preschool-age children. Although working mothers today still are penalized in countless ways -- while studies show that fathers are rewarded for parenthood -- Ida Phillips' case at least put the law on their side.

Title VII also was deployed to strike down employer policies that explicitly punished pregnancy, ranging from automatic firing to forced leave to erasing women's seniority while they were out having their babies.

After the Supreme Court in 1976 issued a widely reviled decision limiting employers' obligation to provide pregnant workers the same kind of disability benefits afforded other workers, Congress amended Title VII by passing the Pregnancy Discrimination Act, making explicit that discrimination because of sex included discrimination because of pregnancy.

Of course, that doesn't mean such bias is a thing of the past -- far from it; pregnancy discrimination charges filed with the EEOC and related agencies have surged in the past two decades and can still be startlingly blatant. But now there's a legal remedy to fight it.

Stereotypes

At issue in so many of the early Title VII sex discrimination cases were stereotypes -- about what jobs women want to do, what jobs they're able to do and about whether, by nature, they are mothers first and workers second. But the most famous court case about sex stereotypes concerned more subtle barriers, those posed by norms of "feminine" appearance and behavior.

In the early 1980s, Ann Hopkins was the only woman out of 88 candidates seeking promotion to partner at the Big Eight accounting behemoth Price Waterhouse. Despite having won more business for the firm than any of her male competitors, Hopkins wasn't promoted. She soon learned that the problem wasn't her qualifications.

"Needs a course in charm school," said one reviewing partner. "Overcompensated for being a woman," said another. Even Hopkins' mentor at the firm advised her to "walk more femininely, talk more femininely, dress more femininely, wear make-up, have your hair styled, and wear jewelry."

The Supreme Court ruled that penalizing a woman for not looking or acting like the right kind of woman is just as discriminatory as penalizing her for being a woman, full stop. "If an employee's flawed 'interpersonal skills' can be corrected by a soft-hued suit or a new shade of lipstick," noted the vourt wryly, "perhaps it is the employee's sex and not her interpersonal skills that has drawn the criticism."

Price Waterhouse hardly put an end to the Catch-22 in which working women perpetually find themselves: Speak up and you're a bitch; emphasize your warmth, and you're too soft to lead.