Most of our progress on the wage gap was in the '80s and '90s. What gives, 21st century?

The gender wage gap has improved quite a bit since women started entering the workforce in large numbers. Women who work full time and year-round earned just 58 percent of what men earned annually in 1968; now that ratio is about 79 percent.

But looking at also tells us something depressing: Most of the progress on closing the gender wage gap was made in the 1980s and '90s.

Since 2001, the gap has only closed 2.3 percentage points. (From 76.3 cents on the dollar to 78.6 — that "79 cents" figure is rounded up.)

What gives, 21st century?

"A lot of the gains we saw in the '80s and '90s were by women catching up in terms of experience, and to some extent education — but also overtaking men on education," said Ariane Hegewisch, program director of employment and earnings at the Institute for Women’s Policy Research (IWPR). "It was like a catch-up effect, as well as getting rid of glaring discrimination."

In other words, we've already knocked down the low-hanging fruit. Making more substantial progress will take a lot more effort, and it's not clear everyone's on board to do that work.

Passing universal child care would be an expensive and complicated endeavor, Hegewisch said. But it would relieve working women of the daunting choice between earning a living and taking care of their families.

It's actually not impossible to imagine passing universal child care. We came this close in 1972, before Nixon changed his mind and decided to veto it. Political polarization was less out of control then, though, and we'd need either huge Democratic majorities or a major cultural shift in the Republican Party to get this done in the foreseeable future.

About half of the gender wage gap is attributable to occupational segregation — the fact that men and women tend to cluster in different job sectors and the male-dominated ones just happen to pay a lot more than those dominated by women.

That's a tougher nut to crack, social conditioning and gender stereotypes being what they are — and the stubbornness of occupational segregation is one reason we've seen so little change on the wage gap in the 21st century, Hegewisch said.

Companies in male-dominated industries like manufacturing and engineering can absolutely recruit more women with a concerted effort, though, and IWPR has some interesting suggestions for how they can go about that — for instance, recruiting and training librarians, who are mostly women and who actually have pretty similar skill sets to those required for midlevel computer support jobs.

Plus, there are still a few low-hanging pieces of fruit we haven't bothered to knock down, like requiring wage transparency so that women actually know if they're making less than male co-workers, and so that employers can catch themselves (or be caught by regulators) if they're paying men more due to unconscious bias. Bills like the Paycheck Fairness Act, supported by both Hillary Clinton and Bernie Sanders, will do that, as well as close loopholes in the Equal Pay Act of 1963 to make gender discrimination harder to justify legally.

Actually enforcing the laws we already have would also help, Hegewisch said — including laws about sexual harassment, which research suggests helps drive women out of high-paying tech fields.

And while passing national paid family and medical leave is a political nonstarter in this Republican-led Congress, it wouldn't be that expensive or complicated to implement because it works like disability insurance, funded with very small paycheck contributions. Paid leave would massively unburden the lives of working parents with children, and help women avoid the wage penalty that often goes with even the briefest career pause to start a family.

Women can't do it on their own, though. Leveling the playing field between men and women at work also requires encouraging fathers to take paternity leave — both through policy nudges like Sweden's use-it-or-lose-it program, and subtle cultural changes like Facebook CEO Mark Zuckerberg's decision to lead by example and take two months of leave for the birth of his daughter.

So there you go, 21st-century America. A rough plan for closing, or at least narrowing, the wage gap. What are you waiting for?