Excerpt from The Birth of the Pill by Jonathan Eig, plus links to reviews, author biography & more

Pincus was no mere scientific technologist. He had the soul of a romantic. He looked to nature not only for answers but also for beauty. And here was something beautiful. Between puberty and menopause, women normally produce an egg roughly every twenty-eight days from one of their ovaries. The egg migrates down the fallopian tube to the uterus. If the woman has sex with a man and the man ejaculates, five hundred million sperm fight to fertilize her egg. If the egg is not fertilized, it can't implant itself in the lining of the womb, and if it can't implant itself, it is discharged along with the lining of the uterus. If it is fertilized, after about six days the egg can attach to the wall of the uterus, where the woman's blood will nourish it through the placenta. During this gestation, pregnancy begins: A zygote becomes an embryo and an embryo becomes a fetus. Two sex hormones, estrogen and progesterone, guide this process. Pincus focused largely on progesterone.

Often referred to as the pregnancy hormone, progesterone regulates the condition of the inner lining of the uterus. When an egg is fertilized, progesterone prepares the uterus for implantation and shuts down the ovaries so no more eggs are released. In effect, Pincus recognized, nature already had an effective contraceptive. Progesterone was preventing further ovulation to allow the fertilized egg to grow safe from harm. What if the same contraceptive could be delivered in a tablet form, effectively tricking the woman's body into thinking that it was already pregnant? A woman would be able to shut down ovulation any time she liked for as long as she liked. If she didn't release eggs, she couldn't become pregnant.

To Pincus, it was a solution elegant in its simplicity. It wasn't new. It wasn't radical. It was merely a matter of thinking differently about how to solve a problem.

He and Chang began by repeating the experiment done in Pennsylvania, adjusting the dosages and means of delivery to get a feel for progesterone and how it worked. They started with rabbits. Pincus sent a request for funding to the Planned Parenthood Federation of America, the women's health and advocacy group that Sanger had helped found. He asked for $3,100: a $1,000 stipend for Chang, $1,200 for the purchase of rabbits, $600 for animal food, and $300 for miscellaneous supplies.

"I have $2,000, perhaps a little more," Sanger wrote to Pincus a few weeks after their meeting. "Will this do?"

"The amount was ludicrous," Pincus recalled, "but I at once replied, 'Yes.'"

Excerpted from Birth of the Pill: How Four Crusaders Reinvented Sex and Launched a Revolution by Jonathan Eig. Copyright © 2014 by Jonathan Eig. With permission of the publisher, W. W. Norton & Company, Inc. All rights reserved.