(FORTUNE Magazine) – The effects of some technological changes are obvious, as in the case of the Internet revolution that's shredding and reweaving the fabric of American business before our eyes. But other innovations do their work deep beneath the surface of society. Such is the story of the birth control pill. Not much has been written--either in the popular press or in academia--about the way it has changed the economy and the U.S. work force. One reason is a dearth of data: Until fairly recently questions regarding young women's decisions about sexuality and procreation went unasked. The subject was shrouded in societal taboos.

But the pill has indeed transformed the face of the American labor force during the past three decades, so powerfully that it will surely be regarded as one of the signal innovations of the 20th century. In a new academic study--The Power of the Pill: Oral Contraceptives and Women's Career and Marriage Decisions*--Harvard economists Claudia Goldin and Lawrence Katz unearth and marshal the economic evidence that supports the case. One of their main findings: The pill has had more to do with women's ascent in corporate America than such issues as affirmative action or abortion reform.

Goldin and Katz begin with two facts: The fraction of female American college graduates entering professional programs leaped around 1970, and the age at which these women married soared shortly thereafter. The data suggest that the diffusion of the birth control pill among young, college-educated women was the main reason.

The pill was approved by the Food and Drug Administration in 1960. Although it was quickly adopted by married women, young women were generally denied access to it until the late 1960s, when a series of state law changes reduced the age of majority and in some cases specified that "mature" minors could decide for themselves whether to take the pill. At the same time, colleges and universities began to provide family-planning services to undergraduates, beginning with Yale in 1969.

Wider access to the birth control pill had two kinds of economic effects, say Goldin and Katz. The first--the direct effect--was that it changed fundamentally the educational and career tradeoffs for young women graduating from college, beginning with the horde of baby-boomers born just before 1950. In previous generations a woman graduating from college who chose to delay marriage in favor of a long and expensive professional education--law, business, or medical school, for example--either had to pay the penalty of sexual abstinence or take the chance that her investment might be wasted if she became pregnant and abandoned her career.

The pill's second, indirect effect, which Goldin and Katz call its "social multiplier effect," was that it had an impact on all women, not just career women, and men as well. That's because all individuals could now delay marriage and not pay as large a penalty. Previously, while women who undertook postgraduate training delayed marriage, most of their peers got married, so the universe of eligible bachelors was smaller and more picked over once they finished. Since the pill permitted all young people to delay marriage, it created a thicker marriage market for career women and, as the authors put it, produced "a new equilibrium in which marriages are later, careers more numerous, and matches 'better.'"

The authors examine alternative explanations, including the rise of affirmative action in the mid-1960s and the reform of state abortion laws in the early 1970s, but conclude that the timing of those developments doesn't match the data; that suggests they played a supportive, rather than causal, role.

Finding the information for the study wasn't easy. "I was astounded that there was so little data on something I myself had lived through," says Goldin, whose specialty is analyzing economic evidence from the past. She found no studies or surveys about young women, fertility, and contraception from the 1960s and just two from the 1970s. "When something has been so demonized," says Goldin, "people don't want to ask questions."

* National Bureau of Economic Research Working Paper No. 7527, www.nber.org/papers/w7527.