Women of every color are paid less than men, at all education levels — and it only gets worse as women’s careers progress. And not only in the USA. According to the World Economic Forum, there is no country on earth where women make as much as men for the same work.

The leading issue by experts for the divergence of men and women’s pay is what careers they go into, or what economists call “occupational sorting.” But there is a different theory. Basically, the more women that enter into an industry the lower the pay for everyone!

How does that happen? Because the real issue is gender bias. It sneaks into those decisions. The New York Times spoke with Paula England, a sociology professor at New York University about this very same thing.  “When women move into occupations in large numbers, those jobs begin paying less even after controlling for education, work experience, skills, race and geography” Paula said in to the New York Times.

Paula is a co-author of one of the most comprehensive studies of the phenomenon, using United States census data from 1950 to 2000, when the share of women increased in many jobs. The study, which she conducted with Asaf Levanon, of the University of Haifa in Israel, and Paul Allison of the University of Pennsylvania, findings were:

Their analysis found evidence of “devaluation” – that a higher proportion of women in an occupation leads to lower pay because of the discounting of work performed by women. -The New York Times

So, in other words: 50 years of data proved that the more women join an industry the less we all get paid. Why? Employers place a lower value on work done by a women. “It’s not that women are always picking lesser things in terms of skill and importance,” Ms. England said. “It’s just that the employers are deciding to pay it less.”

Unfortunately this implies a deep rooted causality for the gender wage gap that a simple law won’t fix. In truth, the key to closing the gender gap is closing gender bias.